Notes on Miller/Router
Contents
1. Open am Close el Save Save As Page Setup b Print CADICAM gel Send Properties Exit lodun wg A373607 MOJA quado por psy JE oN 1 Motor speed control PCB cwe z motor speed control with motor and rearranged circuit cwe 3 C Motor speed control cwe 4 C PCB For project cwz Crid M Chrl 0 Ctrl 5 Export DXF Export MC Drill Copy CAM Data a ot t Galway Education Centre 3 7 CNC Routing Choose a filename and make sure that the Solder Side is checked for export Export Gerber File Name jjects Motor speed control PCB inf Save As Export C RS 274D standard RS 274X extended Export the Following circuit layers Layer File Circuit Board C Documents and Settin Solder Side C Documents and Settin Component Side C Documents and Settin C Solder Side Mask lt amp iw Place each exported layer in a separate output File V Include aperture table within output file Fill pad drill holes Solder mas p 01 i Coordinates Units Format No Zero Supression BE Absolute Sample UUDDD C Incremental e oe Select OK to create the files and exit Circuit Wizard 38 t Galway Education Centre CNC Routing Machining the PCB Next Start VR Milling As there is no file loaded the windows will all appear blank Ep w Ta Metric Skip Block OFF Continuous Cycle Time 00 00 00 Offset Fo2. Projects e Redesign the name plate so that the rectangle stands proud of the top surface and the text is machined into it using a single line font such as Simplex e Design and make a noughts and crosses game e Design and make the square triangle circle game ot Galway Education Centre 31 CNC Routing PCB Manufacture PCB manufacture is quick and easy using the Denford Compact 100 Pro PCBs are made from a material known as copper clad board that consists of a paper based laminate material covered on one side with a thin film of copper The technical name for this material is FR2 The copper can be engraved away to form tracks that make up the circuit on PCB The production of a PCB involves up to three operations e he first is to engrave the tracks and pads using a vee engraving tool e Once the tracks are complete holes can be drilled in the pads to allow the wires from the components to pass through e The third operation is to cut the outline of the PCB to size The last two of these operations are optional and the drilling can be done by hand later if the holes are centre spotted with the engraving tool at the time of machining A vee engraving tool typically makes a cut of about 0 3mm wide when cutting at 0 25mm deep This needs to be taken into account when designing a PCB and enough space needs to be left between adjacent tracks to allow the tool to pass between them If the tracks or pads are made too close toge
3. Make sure that Show Grid and Snap to Grid are turned on 2D GridForm Grid Colour ae Show Grid Snap to Grid Polar Snap Angle Next Select File Import and choose the file NamePlate DXF This file contains the geometry for the outer profile of the sign It was created in Solidworks and exported in DXF format The profile will automatically be moved as close as possible to the bottom left of the billet as shown 1 c i HH The profile should now be moved so that it is not touching the edge of the billet This will make the setup easier later on and will ensure that all edges are machined and clean up properly The profile should be highlighted in pink as shown above If not drag a box around it to select it Next select the Alter Selected Button to move the profile 130 000 60 000 LI a Alter Selected ot Galway Education Centre 19 CNC Routing The profile can now be dragged into position as shown below 130 000 e The next task will be to add a rectangle and then put some text into it Select the Add Shape button to start drawing a rectangle 60 000 L 4 dd Shape Use the snap and grid to create a rectangle 80mm long and 30mm high like that shown below 20 ot Galway Education Centre CNC Routing Select the Text button on the left toolbar and drag a rectangle to place the text inside the rectangle you have just drawn Leave one grid increment between the t
4. increments steps controlled by voltage pulses A stepping motor typically rotates 1 8 degrees per pulse If 200 pulses are sent to the motor it will turn through one complete revolution The speed of the pulse train will control the speed of the motor They are usually used with Open Loop control The second types of motors are AC or DC servo motors These behave in a similar manner to a conventional AC or DC motor but are designed to provide more constant running characteristics These motors will exert a torque in proportion to the current running through them They are used with Closed Loop control only 64 ot Galway Education Centre CNC Routing Open and Closed Loop Control Open Loop This is the simplest type of control and contains the three basic elements described in Figure 32 above otepping Control Motor Unit Figure 33 Elements of an open loop control This is shown in more detail below The open loop system works as follows Say that the control has calculated that a particular axis needs to move a distance corresponding to 80 pulses at a constant speed equivalent to 10 pulses per second The control will output the pulse train to achieve this which is then amplified and delivered to the motor The stepping motor will travel the specified number of pulses and then hold in position until the next action The control has no way of knowing whether the motor has actually received or travelled the full distance Error
5. point will be a CAD model or drawing The workings of CAD systems are not discussed here Types of CNC Machine There are three common types of CNC machines used in the classroom In each case they can greatly simplify the manufacture of an item or in many cases permit the manufacture of an item that would otherwise be impossible The applications of each are described below CNC Lathes These will be a familiar item to many people as they have been in Engineering rooms in schools for many years The most useful application is in the production of parts that have radiused corners tapers and threads that are difficult to produce otherwise Boxford and EMCO are the two most common manufacturers and are described in more detail in a later section Laser Technology Laser is a relatively new technology in the classroom and offers a very versatile and easy means of producing items from wood and plastic materials The machines are very easy to set up and use there is no need to clamp the work piece and behave in much the same way as a printer or plotter The laser machine is driven directly from the CAD system or graphical package being used Figure 1 Laser cutting machine O t Galway Education Centre l CNC Routing There are two main applications for laser machines 1 Laser Cutting Laser cutting is quick accurate and leaves a clean cut It is useful for producing components that would otherwise be marked cut and filed to siz
6. using a computer and loaded into the machine control one line at a time using punched paper tape The programs consisted of long lists of coordinate data that were fed to the control one line at a time for each move This type of control did not have a computer and all of the control was achieved by the 58 ot Galway Education Centre CNC Routing hard wired circuitry of the control system The machines were very expensive very large and used almost exclusively by the aerospace industry CNC The next major development came in 1975 with the advent of Computer Numerical Control Computer Numerical Control uses a computer to perform the tasks formerly done by the hardwired system They machines were much more flexible in operation It was now possible to machine an arc by issuing a single command as the control could now calculate all of the intermediate points along the arc CNC also featured canned cycles where the drilling of a hole or the cutting of a thread on a lathe could be simplified to a single command It was around this time that CNC started to become commonplace and CNC lathes and Milling machines were used both to mass produce simple components and to manufacture difficult items such as cavities for injection moulds The machines were programmed by a text based programming system called Word Address more commonly known G Codes because of the appearance of the program The programs are commonly called part programs
7. Tool and Offset Editor Wark Offsets Tooling Data Tool Library xw iia anm DO s Default Offsets ex e eu e A Aus 230 667 g B Y Axis 72 083 gA B Z Is 0 000 H Alloftsets MOF BOETIUS The tool datum is set and stored by defining a Work Offset to store the difference between the machine datum and the work datum for each of the X Y and Z axes If the Work Offsets button is selected the window should look something like that above To set the current position as a work offset select the New Offset button on the top left of the window and type a name for the offset in the text box that appears below Then select the XYZ button to store all three axis positions Alternatively to even out error for large workpieces that may have an uneven height Select X and Y individually and set the Z datum at the centre of the work piece after moving there Tool and Offset Editor Wark Offsets Tooling Data Tool Library Millia ez vea ei P Ais 244150 A E Y Axis 131 250 pg B Z Axis 56250 f js AllOttsets MOF GSEs sistema Once the offsets have been set the values for the X Y and Z axis offsets will change to reflect the current position from the machine datum A number of work offsets can be defined and stored for later use The work offsets can be recalled later if the same job is to be run again 48 ot t Galway Education Centre CNC Routing Defining Tools In order to accurately machine a
8. and how deep needs to be added As well as this heights for clearance moves between profiles speeds and feeds need to be entered also Taking this into account a simple 2 D part will often be more complex to set up than a 3 D one Machine manufacturers tend to each take their own approach to addressing these issues The following section deals with the QuicKCAM system only Main Considerations in Setting up a 2 D Part Consider the desk tidy project shown below Figure 21 Desk Tidy project ot Galway Education Centre 15 CNC Routing eU A d Figure 22 Desk Tidy before bending Note that the roughing toolpath has been omitted for clarity in this example In order to produce the part accurately the tool must cut to the correct side of the profile as shown below To do this the diameter of the tool must be known beforehand It must also move clear of the work piece when moving from one profile to another and move to the correct depth of cut afterwards In addition the area in side the pocket must be machined away to the correct depth Figure 23 2 D profile showing tools and offsets 16 t Galway Education Centre CNC Routing This is done on the Denford machine using a Machining Plan for each of the contours A machining plan allows the speed feed depth direction of cut and offset to be defined for each profile There are also machining plans for pocket milling and drilling holes 2 D Machining on the De
9. formats were to be supported ot Galway Education Centre 51 CNC Routing The partially complete diagram above gives an idea of this Each of the arrows represents a conversion routine to another file format To further complicate matters software manufacturers rarely publish the format of their native file formats and in any case they are prone to revision without notice as the software is updated and developed In practice a neutral file format is usually used to transfer data from one system to another The file format is published and understood by all 52 ot Galway Education Centre CNC Routing Neutral System file E format System B System It can be seen that this arrangement is much simpler Each software package needs only one translation routine to import from and to export to the neutral file format To convert data from any system to any of the others a file is exported in the neutral format and imported by the receiving system The neutral file format itself will by its nature be a compromise and there will often be some loss of system specific information e g the design tree in SolidWorks in the translation However this does not pose a problem as these features are often not needed by the system subsequently reading the file for example a machining program such as Visual Toolpath is only interested in the physical shape of the solid A few different neutral file formats have evolved over tim
10. of the part to be made rather than just a two dimensional profile as previously The starting point is to generate a solid model of the item to be made using CAD software such as SolidWorks This is then exported into the 3 D software where toolpaths are generated for both the roughing and finishing of the item The software is often wizard based and leads the user through a series of logical steps through the process of preparing the machining sequence Graphical simulation of the toolpath allows a realistic preview of the part to be generated 3 D machining is one of the most powerful features of the desktop router and should contribute significantly to the development of Technology projects Figure 5 CAD model of part Figure 6 Model of part showing toolpath 4 O t Galway Education Centre CNC Routing Figure 7 Machined part 3 D Scanning In 3 D scanning an existing component can be reverse engineered by using a touch probe to capture a grid of points on its surface and store them as a CAD model This is particularly useful where an existing complex part exists that needs to be copied or have something machined or engraved onto its surface The way of making a 3 D scan is not very different from using a 2 D scanner to scan a document The main difference is the third dimension In a conventional scan the area of the page to be scanned is defined before performing the scan With 3 D scanning it is necessary to define a box a
11. part the software must know the dimensions of the tool being used Tools are defined using the Tool and Offset editor and are accessible from the other software e g QuickCAM There is an extensive library of tools already defined in the Tool Library These can be viewed by clicking on the Tool Library button Tool and Offset Editor Work Offsets Tooling Data Tool Library Ball Hose m Nose 1 8 Ball Nose Ball Nose 2 mm Ball Nose Ball Nose 3 mm l Ball Mose Ball Nose 6 mm i Ball Nose amp Slot Drill 1 5 mm l Slot Mill Slot Drill 2 mm l l Slot Mill Slot Drill 3 mm Slot Mill Slot Drill 4 mm i Slot Mill 7 Slat Drill 5 mm Slot Mil C lek Mell C eae C l k AI All0ffsets MOF gets staan Tools can be added or removed from the library using the two buttons on the top left of the window To select the tools for use in a particular job choose the Tooling Data button to show the list of active tools The blank Tool Data window looks like this Tool and Offset Editor work Offsets Tooling Data Tool Library M3 xS Tool 1 VE Sap rA u o Undefined Description Diameter Tool offset 0 000 A ea UnDefined Length Flute Length ooo 0 000 All tisets MOF Etisal A tool can be added from the library by clicking the top left button to display a list of tools in the library t Galway Education Centre 49 CNC Routing Library Tool Selector 1 Ball Nose 1 4 2 Ball H
12. A TECHNOLOGY SUBJECTS SUPPORT SERVICE Leaving Certificate Technology CNC Routing amp Applications Denford Compact 1000 Pro Contents Applications of CAD Cam in Schools eeeeeeeeeeeeeeeeeeee 1 Types or CNC Machines cooisanes smepieon imus eusdotsteus te upin usto opea stor pex See Pr dcas 1 CNG Routers MillS i 3 CNC ROUTING MTOdUCUON CR 9 Characteristics of the Denford Compact 1000 Pro 9 Operation of the M CHING ccccecceeeeeceeeeeeeeteeeeeeeeeeeeeeeeaeeeeeeeeenaes 10 ZD eealllae RE Tm 15 21 Machining EXE OISE suain esa masa tud adum aste eet nE Eren Rede RETENAR 18 Working with VR Milling cece cece eecceeceeeeeeceeeeeeseeeeeeseeeeeeaeeaeeeeeeaeegees 28 giis 31 PCB Manufacture sssesssssssssssseeeennen nennen nennen nnne rns a nna nnns 32 Designing and Manufacturing a PCB eeseeeeeeeeeeeeeeeee 34 Machining Me POB x cccncigesencovpasssconssasosecoasesseraaanoqeaseesecespsosesesyenersrartaoreaee 39 APPEN dier T E E A 45 POO AZ ere E E AE 51 nS CAD CAM cm 58 CNC Routing Applications of CAD CAM in Schools This section will first look at the types of CNC machines commonly used in a school setting Then for each type of machine an overview is given of the range of processes possible for it For many of the processes the starting
13. B For project del E PCB For prajeck gb Ei PCE For project gb Ej PCB For project gb H PCE For prajeck gb3 Uses Export PCB manufacturing data from CAD to CAM Advantages A well established and easy way to convert specialised data for PCB Allows filtering out of unwanted items by ignoring certain files e g component side Limitations Useful for PCB manufacture only ot Galway Education Centre 57 CNC Routing Origins of CAD CAM Introduction The term CAD CAM stands for Computer Aided Design and Computer Aided Manufacture The two are often used together to describe a process where an artefact is designed electronically using a CAD system such as SolidWorks or AutoCAD with the information from the CAD drawing being used to manufacture the component directly using computer controlled equipment such as a milling machine or lathe Over time both CAD and CAM have evolved separately and the seamless combination of the two is a relatively recent development This module will assume a working knowledge of CAD and will concentrate on the manufacturing aspects of the process There is a variety of CNC machine configurations manufacturers and an even greater variety of processes available to the Technology teacher It would be beyond the scope of this document to give a comprehensive treatment of each machine each process and its associated software application Instead a general overview is given of what is possible and how t
14. Denford routers for example use a version of the language known as Fanuc OM So called because it is used by the GE Fanuc CNC control which is fitted to many machines There is a variety of software packages available to generate programs These take the CAD data and post process it to produce a CNC program that is then loaded into the machine control from the CAD computer using a cable ot Galway Education Centre 59 CNC Routing This type of software combined with the CNC is commonly referred to a CAM system Computer Aided Manufacture The entire process is usually referred to as CAD CAM The two most important functions a CAM program performs is to first add in extra information that the CAD drawing would not have such as cutting speeds feeds clearance moves tool offsets etc It then generates a G Code program in the correct format for the machine it is being sent to These programs are often very long several thousand lines as they are commonly used to machine items such as mould cavities where many short moves are required The process is shown in Figure 27 Figure 27 Schematic of the CAD CAM process CAM systems usually offer some means to preview the toolpath or simulate the cutting process before generating the program They often offer a CAD like drawing functionality that eliminates or reduces the need for a CAD system There are a variety of CAM systems commercially available AlphaCAM is one system that is popul
15. PCB otart the process of converting the circuit by clicking on the icon at the top right of the toolbar amp Convert to PLE Layout Convert a circuit diagram into a printed circuit board PCB layout 34 ot Galway Education Centre CNC Routing Click Next and select the Single Sided Thick Tracks option as shown below Convert to Printed Circuit Board Choose how you wish to convert your design into a PCB layout and then click Next Eo continue ae Single Sided Thick Tracks Y Single Sided Normal Tracks oe Single Sided Thin Tracks Y Double Sided Thin Tracks r Placement Only Na Routing Es Rats Nest Mo Placement ar Routing amments Creates and routes simple single sided boards with large pads and thick tracks Slow me to customize the PCB layout conversion Back Cancel Help Accept the defaults for all the following dialogues until the conversion is complete The PCB should now look like that shown below Ma 4 4400 1 c S The PCB is now ready for manufacture However if desired the placement of the components and track widths etc can still be changed if desired First make sure that Interactive Routing is enabled hv Check Integrity Insert Met Im Lack Mets pai Optimize Mets m Suto Optimize SS O o t Galway Education Centre 35 CNC Routing Now drag and rotate any of the components to a different position on the PCB note the r
16. The programs are keyed directly into the machine control or else generated elsewhere and then downloaded to the machine There is some variation in the format and syntax of word address programs due to different adaptations of it by a range of CNC control manufacturers A fragment of a typical part program for a milling machine is shown in Figure 26 below N5 GOO G90 X100 0 YO 0 T1 M06 Rapid to tool change position Load Tool 1 N10 G43 X5 0 Y 5 0 Z1 0 S1200 M03 M08 Move to start of profile Start spindle N15 G01 G41 Z 5 0 F100 Feed to depth N20 X90 0 Linear cut along profile N25 G03 XI00 0 YI0 0 710 0 10 0 Circular arc move Figure 26 Sample of a G Code part program Using this system the programming of simple parts is relatively straightforward and making changes to a program is easy However manual programming by its nature is prone to error and for more complex shapes such as curved or sculpted surfaces the program needs to be generated from a CAD system CAD systems themselves originated around the same time as the early NC machines but remained expensive and therefore rare until the advent of cheap computing in the early 1980s when they started to become commonplace Having defined the shape of a part to be manufactured using CAD the next logical step was to use the CAD geometry to generate a program for the CNC tool directly thus eliminating the need to write programs like that shown in Figure 26 above This approach is still common
17. ar with the manufacturing industry in Ireland at present Present Day With the reduction of the cost of CNC systems and computing a variety of light desktop machines have emerged in recent years These were originally aimed at the modelmaking industry and offered a low cost alternative for the cutting of soft materials such as wood and plastic These machines often share many of the characteristics of a printer and offer a graphical programming system where the user has little or no need to interact with the programming language used by the machine Unlike the complex user interfaces seen on full size CNC machine tools these machines usually offer two or three buttons to perform the essential tasks such as setting up a cutting tool The machines can be controlled using a printer driver or from other software on the computer This effectively replaces the machine interface This method is very simple to use and has been adopted widely in schools for routing machines vinyl cutters laser cutting etc 60 ot Galway Education Centre CNC Routing Types of Machine In CNC the location of the cutting tool is specified by its position along two or more of the machine axes An axis is can be considered as a degree of freedom or a direction along which the tool can move and roughly corresponds to the cartesian coordinates x and y used in CAD With CNC the situation is a little more complex however as explained below Axis Orientation The axe
18. asing or decreasing the number of triangles but in general this is not necessary Advantages This is a quick and simple way of exporting a complex 3 D solid modelled shape to another system or Galway Education Centre 55 CNC Routing Uses Export of a 3 D solid modelled part to another system for machining or rapid prototyping Limitations e All of the design and other information colour texture etc are lost so this is not suitable for export to another CAD system for example that may want to use this data e tis not suitable for exporting importing anything other than solid models Windows Metafiles These are the files that are created when items are cut and pasted using normal windows commands Edit Cut Copy and Edit Paste Entities can be copied from one program and pasted into another In some cases this is the only possible way to export import between different software and in many cases it greatly simplifies the process There are some limitations however Advantages Allows the cutting and pasting of a wide variety of data such as text pictures of all types CAD drawings across widely different software For example a 2 D CAD drawing can be pasted directly into a word document or into another CAD program or into an image editing program such as Paint in exactly the same manner Uses e When exporting CAD files containing text for laser cutting e When exporting CAD files containing 2 D profiles
19. cept for a window containing the program just generated On the right are a number of options that control the display These can be switched on or off as required Show Hide Window with simulation of Billet and machining of part Select Virtual Machine Select Real Machine 28 t Galway Education Centre CNC Routing To simulate the program select the 2D 3D button to display the simulation window Simulation BET AbOtCOGtseeee2e 00 D Design ings Seamus Gordon My Documents D x 0 000 Y 0 000 z 0 000 F 0 0 5 8000 0 T 2 6 0 M 0 U NI Just Ae NN N30 430 8 ET LA M Chin Black NEF Cantina iei ie Puella Time Dii N E Intitlad fre Iiffsar Far TA Tact Part Notice the four buttons on the bottom right of the screen They behave like the real machine even requiring a program rewind before being able to run the program Rewind the program using the blue button This will enable the green Run button on the left E on PEETRE TTT PS n Virtual Reality CNC Milling COMPACT 1000 PRO File Simulation Setup Windows Utilities Help E 5 simulation PSPK 9 9099 9 9 09 mMy Documents Denford Cl py of 1076 Wa pau AC Y DKI Ki LO grema CES D DIES SEARA PSAL REEI CEARA tals HAAREN ATAA E e t Galway Education Centre 29 CNC Routing Cutting the Part on the Machine Fitting a cutting tool to the machine The machine uses a standard coll
20. d Left arrow keys X Axis Up and Down arrow keys Y Axis Page Up and Page Down Z Axis Home Jag A JOG Ue The axis motion can be continuous at a preset speed e g Ata 865mm min shown in the figure 865 46 ot Galway Education Centre CNC Routing Home Jag A JOG i 222 Alternatively the jog can be set to move by a fixed amount for every keypress 0 2mm in this instance In both modes the step size speed is adjusted using the pm i black dial underneath the jog button Using a small step increment is particularly useful when approaching the top of the work piece with the tool when setting the Z datum One way of setting the datum is to move the tool to within a small distance of the top surface of the material using constant motion and then to step down in small increments 0 1mm or less until a strip of paper held under the tool is trapped between the tool and work piece For positioning the X and Y axes lining the centre of the tool up by eye is usually good enough provided the item is being machined from an oversize blank Setting the Work piece Datum Point Assuming that the tool has been positioned at the datum point on the work piece the next task is to set this position up as the datum point for the machining This is done using the Tool and Offset Editor This can be toggled on and off by the button on the bottom left of the screen ot Galway Education Centre 47 CNC Routing
21. e CNC Routing Setting this point as the datum for the machining is an important task and is dealt with in detail in Appendix 1 Tool Length offsets It is common to use the top of the work piece as the datum for the Z axis i e Z 0 for the top surface of the billet Figure 18 Location of the Z axis datum This is obviously not the same as the machine zero Furthermore when a cutting tool is fitted it will project down below the machine zero The machine will have to compensate for the gap between the tool and work piece when calculating where to move ij Figure 19 Gap between tool and work piece This is further complicated when several tools e g a roughing and a finishing tool are used as they may have different lengths t Galway Education Centre 13 CNC Routing Figure 20 Tools of different lengths To compensate for this each tool will need to have its height set before it is used In practice this process is made a little simpler by using only one tool per program and using two or more programs if necessary 14 ot Galway Education Centre CNC Routing 2 D Machining General Issues relating to 2 D machining The following points apply to 2 D machining across all applications This type of part consists of one or more profiles each machined at a constant depth Clearly a two dimensional drawing of a single profile cannot represent the part completely and information regarding where to cut
22. e It allows intricate parts to be cut that would otherwise be very difficult to manufacture Laser offers an attractive alternative to milling for acrylic or wood based materials Figure 2 Laser cut parts from Acrylic 2 Laser Engraving It is possible to take an image such as a photograph or other graphical image and engrave it onto wood or plastic using a slightly different machine setting than that used for cutting The quality of the image produced is very good Figure 3 Laser engraved image onto clear acrylic 2 ot t Galway Education Centre CNC Routing CNC Routers Mills A router can be classed as a type of milling machine that allows very fast cutter travel combined with very high spindle speeds However routers have a relatively low stiffness compared with a conventional machine These machines are ideal for machining plastics wood modelling foam etc but usually are limited to non ferrous metals at best due to the lack of rigidity A desktop router typically comes with an impressive set of software and ancillary equipment considering the low cost They are extremely versatile and can be used for a variety of purposes A typical machine will offer the following capabilities 2 D Profile Cutting CNC routers can be used to machine shapes consisting of lines arcs and curves from sheet material The machine is usually driven by a 2 D machining software package such as TechSoft 2 D design This allows the profiles o
23. e each with its particular strengths and applications These are explained briefly on the following pages ot Galway Education Centre 53 CNC Routing Drawing eXchange Format DXF DXF was originally developed by Autodesk the writers of AutoCAD as a neutral format for exporting and importing 2 D AutoCAD drawings Although it supports 3 D it is normally used for the transfer of 2 D graphical files between systems It represents the items as lines arcs points etc along with their coordinate data ENTITIES 0 LINE 5 27 100 AcDbEntity 8 0 6 CONTINUOUS 62 1 100 AcDbLine 128 6588971478 20 123 3424833098 30 0 0 11 Advantages It is supported by most 2 D graphical programs as well as the drawing editor in SolidWorks DXF files are accurate to six decimal places and so are suitable where accurately produced parts are required Uses DXF is best used in the following situations e Exporting a SolidWorks drawing for 2 D machining e Exporting a SolidWorks drawing for laser cutting Limitations e he way DXF files represent text means that it will usually not be read by the system importing the file and text will often disappear altogether e DXF files are not suited for transferring drawings containing bitmaps or similar raster images 54 ot Galway Education Centre CNC Routing In most software DXF file creation is available as an option under either File Export or File Save As and selecti
24. e and letting the software generate the cut depths and toolpath Bitmap image Converted to 3 D surface Machined Lithopane Figure 13 Stages in the production of a lithopane image Production of a lithopane is very easy and quick and is expedited by a Wizard that moves through the process step by step 8 t Galway Education Centre CNC Routing CNC Routing Introduction This section deals with using the Denford Compact 1000 Pro routing machine and the material contained here is specific to it Denford provide a comprehensive set of tutorials for using the various options and it is recommended that these are worked through thoroughly GuickCAM 2D Design Shortcut F e KB QuickCAM PRO TE un miling v5 a hortcuE Na Shortcut KE ASS KB 1 78 ouickCAM 4D Shortcut 2 KB The three important software packages needed to use the Denford are as follows Application QuickCAM 2D Design 2 D profiling work QuickCAM Pro 3D Machining Lithopane Machining VR Milling V5 Provides the Machine Interface Simulates Virtual Machine Output from the QuickCAM systems is directed to VR Milling for output to the CNC Wizard for PCB production Characteristics of the Denford Compact 1000 Pro Router The Denford Compact 1000 Pro is a three axis routing machine The table area is 400mm x 240mm with a working height of 80mm approximately The machine head is mounted on a gantry which provides movement along the X axis Th
25. e machine table moves to provide a Y axis The head can travel upwards and downwards to provide the Z axis The machine spindle can hold tools up to 13mm diameter and rotates at 18 000 rev min The tool can travel at up to 4 000mm min in the X and Y axes This is faster than a conventional metal cutting milling machine The machine can cut soft materials e g plastics and wood but as well as non ferrous materials such as Aluminium The machine is programmed and controlled via a suite of software that is supplied with the machine Although all the programming is done graphically the machine itself is driven by conventional G Code Word Address programs The program is generated automatically by the Denford software and appears in a window during a program run Normally there is no need to interact with this code and it is not dealt with further here ot Galway Education Centre 9 CNC Routing Operation of the Machine The machine is controlled via the Denford Virtual Reality CNC Milling software package This software performs two functions 1 It provides an interface for setting up and running the machine 2 It offers a virtual reality simulation of the machine with an identical interface to the real one and a realistic 3 D simulation of the working of the machine itself amp Virtual Reality CNC Milling COMPACT 1000 PRO File Setup Windows Utilities Help VR 3D 2D Simulations B9 7 cd5d 47 2200 8 Control Panel Program P
26. e of configuration allows the machining the top sides and underside surfaces of a component without the need to turn it over Figure 31 Router with a fourth rotary axis t Galway Education Centre 63 CNC Routing Principles of a Practical CNC Control All practical CNC systems contain three elements e he control e Current Amplifiers e Servo Motors Current Amplifier Servo Motor Figure 32 Block diagram of a CNC system The control is the brain of the system The control reads the instructions from the program and performs all of the calculations and measurements that determine where the cutting tool should be for any given instant in time during the run of the program This can be a complex process using advanced mathematical principles The result is that the control can send signals to the servo motors to control the axis positions up to several hundred times per second The type of signal sent depends on whether Open loop or Closed loop control is used see below The output from the control is usually a small voltage typically plus or minus five volts In order to drive the servo motors a current amplifier is needed This uses the voltage signal from the control called the demand voltage to control the current that powers the servo motors The servo motors are the final part of the system There are two types commonly used Stepping motors are a specialised type of motor that moves in very small
27. et chuck similar to those used in industrial routers When fitting a new tool always make sure to fit the collet to the nut first There is a retaining ring inside the nut that engages with the undercut in the collet The collet should engage in this with a click The tool can then be fitted to the collet and only then should the assembly be screwed into the machine arbor 30 ot t Galway Education Centre CNC Routing When the nut is next removed the retaining ring pulls the collet free of the machine arbor thus releasing it If the collet is not engaged with the nut the nut will simply come off leaving the collet tightly stuck in the arbour Removal will invariably require force or impact which will likely damage both the collet and machine over time Running a program To run the program on the machine hide the 2D 3D simulation window and select the Real Machine option instead The program is run in exactly the same manner To increase the speed and fluidity of the movement of the tool set Turbo Mode to on before running the program Otherwise the program will be run one line at a time Where many small moves are involved such as the case here there will be a noticeable difference as the tool comes to a stop at the end of each move MAKE SURE THAT THE CORRECT TOOL IS FITTED AND THE CORRECT OFFSETS ARE ENABLED AS DESCRIBED IN APPENDIX 1 OTHERWISE THE TOOL MAY COLLIDE WITH THE WORKPIECE OR MACHINE TABLE CAUSING DAMAGE
28. ext and the boundary as shown TEXT specify width height LO Now the following dialogue will appear 2D Add Text Font AaBbYyZx Alignment Height Insertion Point Ratation 30000 Width Factor 1 29 fe 20 000 1 al T al Tl Oblique Angle C Upside Down Backwards In this example the Arial font chosen will give Thick letters that can be left as islands in a pocket An alternative would be to choose a font such as Simplex that could be engraved directly onto the surface of the work piece Note that the width factor has been set to 1 25 This provides additional space between the characters and so allows a larger tool to be used for the machining ot Galway Education Centre 21 CNC Routing Select OK and the text should appear as follows Q QO If the text is not evenly placed in the box turn off the Snap to grid option using the button on the menubar at the top of the screen and use the move command to place it on centre spare VIEM LID ut a This completes the creation of the geometry The next step is to create machining plans for the profiles and to generate the program 22 ot Galway Education Centre CNC Routing Creating Toolpaths and Machining Plans All aspects of the machining of the part are dealt with by the CAM Wizard It can be run by clicking on the button on the top toolbar 2 The first step in the Wizard is to choose the material bei
29. f the items to be imported from a CAD system and cut on the machine Features such as holes pockets and bosses can be produced as well The user interface of these packages is often basic and drawing and editing of complex shapes is best completed before exporting the data from the CAD system PCB Manufacture Manufacturing a PCB from copper clad board allows versatility in Technology projects where a pupil can design a circuit and then manufacture a PCB to fit a particular project or application Because there are no toxic chemicals involved as is the case with PCB etching it is a very suitable process for the classroom In order to manufacture the PCB a specialist PCB manufacturing software package is used One such package is TechSoft PCB design and make The PCB design is generated beforehand using software such as PCB Wizard or Circuit Wizard and then imported into PCB Design and Make From there it is a relatively simple matter to machine the tracks and holes as the software handles the details of tool offsets cut depths sequencing etc PPL essan y qi BU iB V B tidie PCB Design PCB Artwork Machined PCB Figure 4 Stages in PCB manufacture t Galway Education Centre 3 CNC Routing 3 D Machining Machining of complex parts such as forms for vacuum forming moulds and models requires a 3 D machining software package This differs from the 2 D software in that it can import a three dimensional representation
30. for laser cutting DXF preferred e When exporting raster images for laser engraving Limitations e All the items are transferred using integer arithmetic and will appear as a picture object when they have been pasted This means that there is likely to be some loss of accuracy It is usual to have to resize the pasted item back to its original size before processing e Effectively limited to any item that can be represented as a picture i e 2 D profiles PCB layouts raster images etc not 3 D entities such as CAD models 56 ot Galway Education Centre CNC Routing Gerber Files Gerber Files resemble CNC programs in appearance and this gives some clue to their origin They were originally developed to drive the Gerber Photoplotting machines that were used in producing masks for PCB manufacture Gerber files can contain all of the manufacturing information relating to a PCB Gerber files are usually generated in a set from a PCB design package each file defining one aspect of the PCB For example one file will contain the details of the tracks solder side and another the sizes and layout of the components component side yet another the drill holes and so on The files are generated automatically using File Save As or File Export option from the PCB design package PCB manufacturing programs are able to read Gerber files directly so this provides an easy means of transferring data from one system to another PC
31. hey are easy to use and can produce spectacular results Each is discussed in more detail below Engraving Engraving is a means of creating reliefs raised engravings and engravings on flat and curved surfaces Items such as text or a 2 D profile are given a thickness and then projected onto the surface of the object to be machined Items such as text or line drawings are commonly used to make engravings Engravings can be made on existing solid objects if the surface of the object to be engraved can be captured using a 3 D scanner see above beforehand Images can also be engraved onto surfaces generated in CAD Figure 11 Relief on a curved surface Lithopane Machining A Lithopane is a special form of image where a greyscale can be reproduced by machining a translucent material to varying depths The deeper the cut the thinner the remaining material and the more light that can pass through it By varying the depth of cut lighter and darker areas can be produced When lit from behind the image is visible High quality monochrome images can be produced in this way ot Galway Education Centre 7 CNC Routing Figure 12 Lithopane machined from translucent plastic back lit and mounted in a frame Lithopane machining is very easy to do using the specialist software accompanying Denford and TechSoft routers It involves taking a scanned image or digital photograph converting it to a greyscale projecting it onto a plan
32. his may be achieved Then a machine specific example of each is presented with enough detail for it to be replicated in the classroom In addition to this a brief summary of the development of CAD CAM is given as well as a section on the principles behind CNC History Computer Numerical Control All of the manufacturing equipment used involves controlling the movement of a cutting tool of some sort in a precise manner Both the positional accuracy and speed of travel are important and these need to be controlled precisely in order to achieve the desired outcome This control of the tool path is achieved by Computer Numerical Control CNC systems built into the machine tool The systems have two aspects e How they control the motion of the cutting tool e How they are programmed In order to better understand how present day systems have come about it is useful to look at the development of CNC over time Early Numerical Control As early as the late 1940s as the cold war between the US and Russia escalated the American aerospace industry began to need complex aerofoil shapes to cater for aircraft and missile manufacture These shapes were very difficult to machine by conventional processes and the first Numerical Control NC milling machines were developed for this purpose The machines had what is known as a hard wired control system and were capable of moving from one point to another in a straight line only The programs were generated
33. ith the normal solid simulation They will become clearer if the Show Toolpath option is selected by clicking on the button on the top of the simulation window t Galway Education Centre 43 CNC Routing Producing the PCB on the Machine Machining the PCB is very similar to producing the 2D part made earlier select Real Machine on the Right hand of the VR Milling window and run the program as before When setting up the PCB on the machine it is useful to have a block of non porous stable material such as Aluminium Nylon or similar large enough to support the PCB and high enough to lift it clear of the table This block can be clamped to the machine table as normal and the PCB blank taped to its top surface using double sided tape If the front left corner of the block is set up as a datum then setting up the PCB blank is simplified and is a matter of aligning the corners of each 44 1 t Galway Education Centre CNC Routing Appendix 1 Setting up Machine and Tool Datum s on the Denford Compact 1000 Pro This process basically involves fitting a tool to the machine spindle positioning it where the datum should be on the material blank and storing this position in the machine s memory The process is explained step by step below First power up the machine and start VR milling The control panel for the machine should appear similar to that shown below This is the basic interface for controlling the machine Contro
34. l Panel Program Position M TX 305 775 un s T d22080 5 Z 75 567 Spindle amp amp Emp m Feed 4 Spindle 1 oog 100 Status Ready Prog F 0 mm min 5 8000 RPM Actual F 0 mm min 5 8000 RPM The machine will not do anything until the axes have been homed Note that the only mode available is Home Each axis can be homed individually or all three together by pressing the button indicated above On pressing the home button the machine will move to the home position and the remaining modes will become available Control Panel Program Position M 5 TX 305 775 m Pr BY 1220892075507 Ez 75 567 spnde e Home Jog Auto MEI 9 Feed 2 Spindle 42 2 100 Status Ready Prog F 1300 mm min 5 8000 RPM Actual F 1300 mm min 5 8000 APM t Galway Education Centre 45 CNC Routing To position the tool at the X Y Datum point select the Jog mode and the window will change to the following Control Panel Program Position M 5 X 5 108 i H1 0 000 Y 49 999 pi z 75 557 Spindle 4 Jog Auto MDI 2 25 L4 Feed 2 Spindle 1004 100 status Ready Prog F 865 mm min 5 8000 RPM Actual F 865 mm min 5 5000 RPM In order to work the window must be active i e clicked upon The green button shown turns red when the window is inactive When the Jog window is active the machine axes can be moved using the following keys on the computer keyboard Right an
35. lable in stationery shops leaves a residue that can be cleaned using a solvent such as paint thinners For workpieces that are not suitable for tape they can be mounted on machine table using the clamp However more care must be taken to ensure that the tool does not interfere with the vice The datum for most operations will be the bottom left of the work piece as one looks in from the front of the machine Setting the machine datum to this point is a relatively simple matter and is dealt with next Figure 15 View of the machine table t Galway Education Centre 11 CNC Routing Preparing the Machine for Use The machine offers a simple and user friendly means of setting up cutting tools Before looking at this it is necessary to understand the issues involved Machine Datum Points When first powered up the machine needs to locate a homing point on the X Y and Z axes This provides an accurate and repeatable means of zeroing each of the axes and means that even if the machine is powered down it will be able to resume work on a partly machined item The machine zero point is located near the top right of the table for the X and Y axes and near the highest point of its travel for the Z Figure 16 Machine Zero point However the work piece datum is often on the top left corner of the blank as shown below and the program coordinates are measured from here Figure 17 Work piece Datum 12 O t Galway Education Centr
36. machining on the CNC 3 Outside Offset 3 000mm Deep w 3 T1 2 500mm Diam 7 in edges 3 000rrn Deep it vi 9 2 b lmrm Diam a Area Clearance 1 500mm Deep 71 2500mm Diam In this example it would be desirable to have the outside profile cut last to ensure maximum grip to the machine table The arrows on the right hand side of the window allow the machining plans to be moved up or down the list to change their order Use the arrows to change the sequence to that below Machin Hans Area Clearance 1 500mm Deep w 8 T1 2 500mm Diam Inside Offset 3 000mm Deep T1 2500mm Diam e Outside Offset 3 000mm Deep T1 2500mm Diam Now that the toolpaths have been created the next step is to verify them and generate a program Select Next to move on to the final stage of the process In the final Post Process stage the toolpath created in the previous step is used to generate a CNC program that is sent to the machine The machine type should be set to Denford metric Milling and the default File name Untitled fnc can be left as is PostiProcess Post Machine Type DENF RD METRIC Miling v C Documents and Settings S eamus Gordon hy D aceumentssDenferd CNC Filess Untitled frie m Sorted Tool Paths 26 t Galway Education Centre CNC Routing If the Check Output button is clicked a simulation of the tool moves will be shown Notice the rapid moves are shown i
37. n Centre 4 CNC Routing The next step is to load the drill file containing the hole data for the PCB The file will have the same name as the Gerber but will have the extension drl Drilling Operations Head Drill File suto C Drilling Depth 2 000 Ie Pilot Erill Orli Tool Na 1 The drill locations will now be visible Once the drill file has been loaded extra options appear depending on the drill data imported Drilling Operations Auto Drill Drilling Depth 2 000 iw Pilot Drill Onl Tool Ma i W 80lmm Tool 2 w 0 802mm Tool 3 Ww 0603mm Tool 4 As this PCB will only be spot drilled make sure the Pilot Drill Only box is checked before moving on 42 t Galway Education Centre CNC Routing The next step allows the speeds and feeds to be changed if desired Leave them at their default values and move on to the next step Speeds amp Feeds T2 Feed 00 000 Speed 23000 T1 Feed 00 000 a Speed 23000 E The final step is to generate a program to machine the PCB CNC Output M Output cutter path v Spot drill all holes Output drilling operation Cut CCw around tracks Create CNC Restart Make sure that the drilling output is turned off before creating the CNC program The program can be simulated using the 2D 3D window as with the 2D Milling exercise As the engraving tool is very small the cuts are difficult to see w
38. n green This step is useful for checking that none of the profiles have been forgotten in the previous stage Once happy click on Post Output to generate the program This will generate the program and will open it in VR Milling for the next stage of the process ot Galway Education Centre 21 CNC Routing Working with VR Milling When the Post Output option is selected in QuickCAM two things happen e he program is generated e Virtual Reality Machining is started up and the newly generated program loaded into it It is important to be aware that you are no longer in QuickCAM but are instead in the machine interface simulation environment QuickCAM still remains running in the background and any changes to the program will require getting back into it and repeating some or all of the operations described in the last section before re generating a new program When it is first run up VR milling will look like the following Virtual Reality CNC Milling COMPACT 1000 PRO File Edit Setup Windows Utilities Help c D G21 do G90 gt 3 Denford Post Output QuickCAM 2D Design enn Date 11 01 2008 Ta Time 18 50 11 DAT Source File C Documents and Settings Seamus Gordon My Documents Denford Cl BILLET X130 000 Y60 000 73 000 l gt Jat Mn Ca N30 G i Metric Skip Block OFF Continuous Cycle Time 00 00 00 Untitled fnc Offset For T4 Test Part The display area is empty ex
39. nford Compact Pro 1000 QuickCAM 2D is used for drawing up and creating programs for 2 D profiled parts It offers a limited CAD like drawing environment with basic functionality It also allows the setting up of machining plans as described above There is a comprehensive user manual outlining the functions of all the drawing and editing tools 2D Design is adequate for simple shapes For more complex designs it may be easier to use a CAD system such as SolidWorks and then import the drawing into 2D Design for machining The issue of file transfer between different software systems has been discussed earlier The issues relating to setting up cutting tools and machine datum s are dealt with in Appendix 1 It is recommended to read this before moving on to the next section The detail of running a program on the machine and machining the part are explained in Appendix 2 ot Galway Education Centre 17 CNC Routing 2 D Machining Exercise The aim of the exercise is to produce the name plate shown below First a partly complete drawing will be imported into 2D Design Then further geometry will be added to it before creating toolpath and machining it Figure 24 Name Plate Project Start QuickKCAM 2D and do the following before starting the exercise 1 Set the billet size to the dimensions shown below 2D Billet Dimensions 18 t Galway Education Centre CNC Routing 2 Select Options Grid and set the grid size to 5mm
40. ng cut Each material has machining parameters such as speed and feed associated with it Soft Wood Model Board Hard Wood MDF Plexiglas HIPS Aluminium CibaT aal Click on Edit to see the details of each material Exit the list and select HIPS High Impact Polystyrene from the list of materials before proceeding onto the next step a in ERES In this step a machining plan is assigned to each of the features to be machined x When first run the window containing the plans is o blank The types of plan available are at the bottom and are self explanatory Fallow oO Inside Offset m 3 Outside Offset 8 Area Clearance faz Raster Clearance Drill T First a plan will be created for the outer profile The t Galway Education Centre 23 CNC Routing tool will need to be offset to the outside and the depth of cut will be 3mm Create an Outside Offset plan and choose the 2 5mm Slot Drill and set the depth of cut to 3mm as shown below 3 Outside Offset Tool T 1 Slot Mil 2 500 2 5mm SO for roughing Slot Mill 2 500 12 5mm SO for roughing outer profiles Depth of cut i 300 a tr Plan Description Outside Offset 3 000mm Deep T1 2 500 iid Contour selection Select All Next select the outer profile of the part It will become highlighted in green and then select Apply The toolpath will be created for the centreline of the tool as shown below in blue ae O
41. ng the correct file type Save As Save in LJ CAD CAM resources v OQ d regnm photos B game 2d Exercise DXF 918 2 D profile in bw DXF B objects only dxf B2dpart For mill with colours dxf BPCB For project dxf B2Dpart For mill with different options DXF Bri2dxf dxf B2Dpart For mill DXF H Sample 2 D part For tutorial DXF B 2000dxf dxf standard dxf dxf B calculator exercise DXF H test For 2 D dxf A 4 My Recent Documents E 2 File name 2DpartformilDXF Save as type Def dsf Drawing drw slddrw Description D My Network Places DXF files are imported similarly by using File Open or File Import Sterolithography Files STL files This file format was originally developed for transferring data between CAD systems and rapid prototyping Stereolithography systems It is commonly used to transfer the physical shape of a solid modelled component from one system to another e g from SolidWorks to a 3 D Machining program for generating toolpath 60 CS CSS PS iS SORS E ee SOM MEL e Figure 25 SolidWorks model of a part and its STL representation In STL the shape of the item is represented by a series of triangles that approximate its outer surface The format can also show which side is the inside and the outside of the part The accuracy of the shape can be controlled by incre
42. ose 1 8 Ball Nose 2 mm Ball Nose 3 mm Ball Nose 6 mm Slot Drill 1 5 mm Slot Drill 2 rim Slot Drill 3 mm Slot Drill 4 mm Slot Drill 5 mm Offset 0 000 Slot Drill amp mm Slot Drill 8 mm m Slat Drill 10 mm Dems gees End Hill 1 5 ram End Mill 2 mm Length 50 000 End Mill 3 SER HL Flute Length 40 000 Choose an appropriate tool Say 3mm Slot Drill to add it to the list If the list is blank it will be added as Tool No 1 A meaningful name for the tool can be typed in the Description line or else leave it as imported from the tool library Tool and Offset Editor Tool 2 Undefined Change Tool Diameter 0 000 Tool offset 0 000 E gt UnDefined Length Flute Length 0 000 m 0 000 AllOffsets MOF DESTE Add one more tool Tool 2 which will be an engraving tool which will be useful for cutting PCBs later Tool and Offset Editor Work Offsets Tooling Data Tool Library Tool 2 PCB Engraving tool 0 3mm Change Tool Diameter a 1 000 v Tool offset 0 000 Eg Engraving Length Flute Length 50 000 i 5 000 E E AllCIffsets MOF Bale TTA MTS Once the tools and offsets have been defined the Tool and Offset Editor can be hidden by clicking on the Icon at the bottom of the screen 50 O t Galway Education Centre CNC Routing Appendix 2 File Transfer between Systems All CAD and CAD CAM systems differ in h
43. osition M TX 341 775 dmm 2 ZY 111 082 525 T Z 75 567 Spinde g At Kl Feed D Spindle 2 1005 100 Status Ready Prog F 0 mm min S 8000 RPM Actual F 0 mm min 5 8000 RPM Metric Skp Block OFF Continuous Cycle Time 00 00 00 j lA new offset The control panel looks like this and contains an emergency stop button and overrides for the spindle speed and feed rate All other functions are carried out using the VR milling software Figure 14 Control panel of Compact 1000 Pro 10 O t Galway Education Centre CNC Routing There are three main aspects to using the CNC routing machine These are e Tool and datum setting e Workholding and operation of the machine e Programming Workholding The table of the machine is made from Aluminium with Tee slots for clamping bolts like a conventional machine The usual way of holding small parts is to use the sliding clamp system shown below It is common to mount a block of stable material on the machine table to raise the work piece up from it A typical block might measure 100mm square and have a height of 50mm The work piece can then be fitted to the top surface of it using double sided tape This is ideal for PCB manufacture and for the machining of acrylic It also has the advantage of offering no obstacles for the tool to collide with during machining The tape used is a special grade that peels cleanly from the work piece afterward The double sided tape avai
44. otate icons are the two visible above the pull down menu in the figure above It should be possible to position the components so that their layout on the PCB is similar to the circuit diagram Make sure that the there is adequate space between the tracks and pads for the cutter to pass between them If not reposition them until a satisfactory result is achieved Save the file once you are happy with the layout Individual tracks can be moved by clicking and dragging on the nodes at the end of each segment The width of a track can be changed by right clicking on it and altering the properties Note that intervention such as this is usually not necessary with simple designs such as this one but it will sometimes be necessary to reduce the width of a track to pass underneath an IC or to re route it around an obstacle on the PCB with more complex designs Use Undo if necessary to revert to the correct design before proceeding to next section 36 t Galway Education Centre CNC Routing Importing the Data from Circuit Wizard to VR Milling Transferring the data between the two systems requires the PCB to be exported in Gerber format from Circuit Wizard To reduce clutter later on delete the copper area on the PCB before exporting so that it looks like this e 1N40Qjz NY Select File CAD CAM Export Gerber f Circuit Wizard Motor speed control PCB cwz E Fie Edit View Project Window Help 1 C Mew
45. ow they work and how they represent the drawing or part being modelled For example a 2 D CAD system will be concerned with lines arcs and their start and endpoints A solid modelling system will need to deal with features such as extrusions cuts and a design tree A PCB design package will have information on tracks pads and component values All of these systems need to save their work to disk for later use As these systems have developed over time each will have devised a file format that is most efficient for their particular needs The format used will be specific to the type of information being stored e g lines arcs and will typically use the least space on disk and load quickly when opened Native and Neutral File Formats It is not surprising therefore that a wide variety of file formats exist for saving CAD CAM data Neither is it surprising that each filetype can usually only be read by the application it was designed for there are a small number of exceptions A list of commonly used file types is shown below There are many more TechSoft 2 D Design Circuit Wizard TechSoft PCB design and make If a particular system was to be able to read in the files from another then it would need to incorporate a routine to read decode and convert the data stored within it To read data from a variety of systems then a similar routine would be needed for each It is easy to see that this would quickly become impractical if many file
46. r T4 Test Part Select File Open Set the file type to Gerber gb and select the gb1 file from the list of files you just created LEk Define Board Width ps 150 000 Height v 50 000 a Auto Size Set the size of the circuit board you are using here If machining double sided boards you must keep this size the same Motor speed control PCB gb t Galway Education Centre 39 CNC Routing Set the board size to suit the PCB 50mm x 50mm is a suitable size for this PCB Note that it is not possible to move or reposition the tracks once they are imported Select Next and set the side to be machined to Solder Side This causes the tracks to be mirrored so that they are machined correctly when looking from underneath Select Side JX Component Side cee Solder Side Turn the board f Horizontally m thee ans Vertically in the rasis The next step is to calculate toolpath to cut the tracks on the PCB Generate Toolpath TodNa z Cutting Depth 0 300 Cutter Diameter 0 250 Additional isolation gap passes Mumber of passes of cutter diameter Calculate 40 ot t Galway Education Centre CNC Routing The toolpath is shown as a white line around the tracks There is an option to generate additional passes to increase the isolation gap The additional passes can be seen above O t Galway Educatio
47. round the volume to be scanned in the X Y and Z directions This is easily done once the size and position of the item on the machine table is known One important issue with 3 D scanning is the usability of the file once it is imported into the CAD system Often the amount of editing that can be done to the CAD model is limited particularly in systems such as SolidWorks that are based on parametric design However for simple applications such as with engraving packages the scanned file is perfectly acceptable Figure 8 Touch probe and part to be scanned t Galway Education Centre 5 CNC Routing Figure 9 The default scanning volume is the entire motion envelope of the machine Figure 10 Small envelope confining scanning to the volume of the component 6 t Galway Education Centre CNC Routing Engraving Carving Lithopane Machining These processes may be less familiar than the more common applications for routers but offer a wide range of opportunities in the classroom They all share one thing in common They involve taking a 2 D object such as a photograph or profile and giving it a third dimension This 3 D object is then projected onto a surface or a plane depending on the application and then machined into it In each case a specialist software application is needed These engraving software systems are usually limited in what they do e g engraving only due to the degree of specialism involved However t
48. s can occur if the motor misses a pulse or if it encounters an obstacle that causes it to stall Pulse Train to Stepping Motor ME lad d Calculate Interpret axis Amplify position and transmit and to generate pulse train program stepper Figure 34 Open loop control system t Galway Education Centre 65 CNC Routing This is not usually a problem where the forces acting on the stepping motor are low or where extreme accuracy is not critical The advantage of open loop is its low cost and simplicity Closed Loop Control This method of control has one additional element Servo motors are used to drive the axes and an encoder is used to provide feedback of the servo position to the control This allows the control to compare the actual position of the axis to where it should be at a rate of about 500 times per second AXIS Position 1 i A M F LN LE 1 E J P yr B i r E p D a 1 k 1 p ko D r E p EL M Control Unit Figure 35 Elements of a closed loop control system The control outputs a voltage in proportion to the amount of error This voltage controls the direction of the servo and has the effect of trying to pull it towards its correct position The greater the error the stronger the pull If a particular axis is programmed to move say 10mm at a speed of 1mm s then it will calculate each intermediate position for the axis in 1 500 second interval
49. s and then vary the demand voltage to pull the servo towards each of them over the course of the ten seconds taken to complete the move Once the move is complete if a force tries to move the axis out of position say a collision with the cutting tool the control will detect an error between the ideal and measured positions and will try to move the axis back into position It can be seen that this type of control is more reliable and offers greater accuracy than the open loop system described earlier Closed loop systems are used widely in CNC equipment and robotics and they are the norm in all but the simplest systems 66 ot Galway Education Centre CNC Routing Actual position from encoder Compare to actual position Calculate Generate Converts desired Voltage voltage to axis based on current to position difference drive servo c z program Current Figure 36 A Closed loop control system ot t Galway Education Centre 67
50. s of a CNC machine are defined by what is known as the right hand rule If we take the thumb as pointing in the direction of the positive X Axis then the second finger is pointing towards the positive Y Axis and the middle finger towards the positive Z Axis The Z Axis always contains the spindle This holds true for all machine tools including lathes X Figure 28 The right hand rule ot Galway Education Centre 61 CNC Routing Figure 29 Axis orientation for Router Figure 30 Axis orientation for Lathe Note that the right hand rule applies here also CNC machines are often described by the number of axes that are controlled A laser cutter would be classed as a 2 Axis device as motion is only controlled in the X and Y axes A CNC lathe is a 2 Axis where the tool is driven along the Z and X axes A router would be a 3 Axis machine as motion is possible in X Y and Z axes 62 t Galway Education Centre CNC Routing Beyond Three Axis Control With some machines it is possible to fit a dividing head and or rotary table to provide rotary motion of the work piece In this case the motion is considered to be rotation about either the X Y or Z axis These rotary axes are usually labelled A B and C respectively Therefore it is possible for a machine to have four five and even six axis control In practice more than four is rarely needed At least one desktop router manufacturer offers a fourth Axis dividing head This typ
51. ther then all of the surrounding copper may not be removed Adjustments to the PCB are best made using the PCB design software PCB Wizard Circuit Wizard or similar beforehand 92 ot Galway Education Centre CNC Routing When designing a PCB it is a good idea to make the tracks and pads and isolation gaps as large as the size of the PCB will allow This makes soldering easier and reduces the chance of over soldering and short circuits The diagrams below show the same circuit The PCB on the left has increased track and isolation gap widths Q e TIP121 i 1 MT The parameters governing the characteristics of the PCB are chosen as options within Circuit Wizard during the conversion from circuit diagram to PCB The soldering of the PCB can be further simplified by machining away all of the remaining copper from the board and leaving just the tracks However boards made this way take much longer to machine so there is a tradeoff involved Drilling Holes on a PCB There are a number of options for drilling the holes on a PCB Holes are recognised automatically and can be either spotted using the vee tool for hand drilling later or else drilled on the router as a separate operation If this option is selected then a tool change will be needed This will involve setting up the drill in the machine in the middle of the PCB production operation and is probably not justified unless a large number of boards are being prod
52. uced as a batch Manufacturing a PCB using the Denford Router Rather oddly PCBs are produced on the Denford system not by any of the QuickCAM packages but by a wizard within VR Milling The PCBs are imported into the system as Gerber files It is necessary to understand a little about the way Gerber files organise data in order to identify what to import O t Galway Education Centre 33 CNC Routing As described earlier Gerber files are a legacy from a time when PCB artwork was created using photoplotting devices made by the Gerber company A PCB is composed of a number of layers i e Solder side Artwork Drill holes etc Each layer would have been separated out into a single file and plotted separately on the machine For this reason when a PCB is exported to Gerber format a number of files are created each containing a specific aspect of the PCB In this case the layers of interest are the Solder Side and the Drill Holes These are often given the extensions GB1 and DRL respectively However some systems combine all of the Gerber files into one large file containing all the data on the PCB Systems that read in Gerber files need to be able to cater for both Designing and Manufacturing a PCB The Circuit shown below is for speed control of a motor This exercise will involve creating a PCB for it and then exporting and manufacturing it First start Circuit Wizard and load the file Motor Speed Control cwz Creating a
53. utside Offset 3 000mm Deep Ti 2 500rnrn Diam 24 t Galway Education Centre CNC Routing Now create an Inside Offset plan to machine the two holes on the part before moving on to machining the text The object is to machine out the pocket defined by the rectangle while leaving the letters behind as islands The pocket will be machined 1 5mm deep To do this proceed as follows Select the Area Clearance plan and set the tool and depth of cut as shown below 8 Area Clearance Tool T 1 Slot Mill 2 500 2 5mm SD for roughing Slot Mill 2 500 12 5mm 5D for roughing outer profiles Depth of cut 15 i Flan Description Area Clearance 1 500mm Deep T1 2 50 Stepover J 40 Contour selection Select All Next select the rectangular pocket and all the entities inside it This is easiest done by dragging a window around them ID imm mmmmmmmmmmmmmmmmmmmmmmmmm mm mmm mm mo ww Eel QuickCAM will recognise the profiles within the rectangle as islands and will avoid them when generating the area clearance toolpath The result should look like that below t Galway Education Centre 25 CNC Routing Reordering the Sequence of the Operations Looking at the list of machining plans in the window they appear in the order that they were created in This is the order they will follow when
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