2009 Version Manual - Mountain Instruments
Contents
1. amount of backlash We need a small amount to allow for expansion and contraction of the system due to temperature variations As such it is ideal to adjust the system at the temperature that is near your normal using temperature however that is not always possible to do Step 11 Re install your motor assembly and replace the cover plate Part 2 Dec Adjustment The actual adjustment procedure for the declination axis is the same as that for the RA The difference is in accessing the dec worm gear Step 1 In order to access the dec axis worm assembly remove the OTA and the counterweights Make sure that the RA clutch screws are secure otherwise the dec can fall to one side or the other Completely remove the clutch knobs Close inspection of the saddle plate will reveal a set of four socket head caps screws in the middle of the plate These screws secure the saddle plate to the top of the dec axis You will need to carefully remove the screws and lift off the plate Set it aside Step 2 Remove the cover plate for complete access to the worm and gear assembly Replace the clutch knobs before making adjustments Step 3 Make adjustments as previously described There are two methods you can use The first method is to make your adjustments to the dec axis without the OTA and counter weights in place This is the easiest however less precise method The second is to make adjustments with the OTA and Counter weights in place Remove the2. cover plate and then reattach the saddle plate and re install the counter weights and OTA Adjustment can then be made under a load If you choose this method be sure to properly balance the OTA prior to adjusting the worm and gear mesh MI 250 Worm replacement Part 3 If the worm assembly of either the RA or dec axis has been removed the following procedure should be used for replacing it in the proper position prior to making final adjustments as described in Step 1 through Step 10 Important The worm assembly can only be removed when the OTA counterweights and declination assembly have been removed from the RA assembly The adjustment procedure is simplified by the use of a piece of key stock available from most hardware stores It is important that the key stock be 25 by 25 square 1 4 x 1 4 and about 1 long When placing the worm assembly back into the mount the angular position of the worm axis needs to be tangential with an imaginary gear center line see diagram By virtue of the MI 250 design manual and go to models the worm has an offset Look closely at the diagram You will see that the left side A of the worm from the left of the worm teeth to the bearing is longer than it s counter part on the right side of the teeth B As such the gear is not being driven by the center of the worm teeth In fact the driving teeth are a couple of teeth to the left side of the center l
3. gt a Mstrumentfs MI 250 Go To User Manual September 2009 Edition Mountain Instruments INTRODUCTION This guide is provided to help familiarize you with the various components of your new MI250 Go To mount The manual is arranged into sections The first four sections cover setting up the mount balancing the OTA polar alignment and the MI 250 Go To Specifications The Gemini instruction will be found on the enclosed CD 7 i Moantan It is important that you read through this guide and familiarize yourself with the PE components that you have received 2 Misuse and misunderstanding of the mount may result in damage to the mount or to your optical tube as well Component Parts of the MI 250 Go To RA assembly also can be referred to as RA Right Ascension or polar base The RA assembly is shipped pre attached to the rocker base also known as altitude azimuth base German declination assembly also known as German dec or dec axis Counter weight shaft Counter weights and counter weight nuts MI8P Pier assembly optional The pier assembly consists of 3 legs with hardware In order to maintain proper worm to gear mesh remove the Dec assembly from the RA for transportation or storage Failure to do so will reduce tracking accuracy Reference Orientation Throughout this manual there are references to the north south east and west of the mount We will assume that the mount is
4. reassembly 11 Refer to worm adjustment section to reset worm Adapter Plate Supplement Your MI 250 is being mounted on your own pier or tripod via the black adapter plate attached to the bottom of the female rocker base To accomplish this you ll need to disassemble the female rocker base from the black adapter plate in order to secure the adapter plate to your permanent pier The sequence for securing your mount to your adapter plate is Removing RA assembly from the female rocker assembly Partial Disassembly of the Female Rocker Removing the Female Rocker from the Adapter Plate Re assembling the female rocker and RA 1 2 3 4 5 Securing adapter plate to your pier top 1 Removing RA Assembly from Female Rocker Assembly Figure 1 The first step in setting up your MI 250 is to remove the RA from the female bottom rocker assembly Begin by removing the altitude lock down hex head nuts Be careful doing this The entire RA assembly is secured by the altitude lock down nuts There is one nut on a post on each side of the RA After removing the two nuts simply lift off the RA and set it aside for the moment 2 Partial Disassembly of the Female Rocker With the RA removed from the female rocker look at the altitude adjustment Examination reveals how this simple mechanical device works Turning the altitude adjustment knob advances or declines the lead screw altitude U nut The c
5. ample if you intend to take a 30 minute exposure there should be no drift for a minimum of 30 minutes 3 2 Altitude Star Drift Once the azimuth drift is completed turn the telescope to point approximately 30 degrees above the eastern horizon and about 0 degrees declination Center the star in the cross hair and watch the direction of drift If the star drifts north the polar axis is too high and needs to be lowered If the star drifts south the polar axis is too low and needs to be raised The first step in making the adjustment is to loosen the altitude lock down handles Then turn the altitude adjustment knob to effect a movement Again before you make an adjustment think it through and practice in the daytime Remember to retighten the lock down handles Go through a couple of iterations with adjusting and re centering of the star You should arrive at the point where there is no drift for as long as your planned exposure If you care to take it a step further go back to the azimuth and re check it With a little practice you can star drift very accurately in about 30 40 minutes The star drift time can be reduced to about 10 minutes using the polar alignment scope SECTION 4 MI 250 Go To SPECIFICATIONS 4 1 RA Assembly 7 5 RA drive 360 teeth Matching precision worm 1 1 ratio worm to motor shaft Class 7 bearings used in worm assembly Conical shape for maximum rigidity cast of 319 aluminum alloy tempered Major pol
6. ar axis bearing 3 74 diameter class 7 Variable friction slip clutch Powder coated and black anodized finish Fine adjustments in altitude and azimuth Total base weight 36 pounds 4 2 German Declination Assembly 7 5 drive 360 teeth Matching precision worm 1 1 ratio worm to motor shaft Class 7 bearings used in worm assembly Conical shape for maximum rigidity cast of 319 aluminum alloy tempered Major dec axis bearing 3 74 diameter class 7 24 pounds total Isolated and removable counter weight shaft 2 each 20 pound counter weights e Pre installed LOSMANDY DA s on saddle plate MI 250 Worm Adjustment Worm to gear mesh is critical to the proper operation and tracking of your MI 250 There may times that you need to adjust your mount By following the steps below proper mesh can be achieved and maintained Please carefully read this document completely and understand it prior to making any adjustments Worm adjustment is easiest to do during daylight hours or in a well lighted environment Part 1 RA Adjustment Step 1 With only the RA axis set up on your pier begin by removing the front cover plate with the MI logo of your RA assembly Set the cover to the side Tighten the clutch screws prior to adjusting the worm Step 2 It is best to adjust the worm to gear mesh under a full load Less the RA cover plate assemble your system with counter weights and OTA You ll also need to balance t
7. ate or dec assembly could hit the handles and damage the unit Use the bubble level to level the pier Assuming you have followed the previous instructions the mount should be oriented north With the drive running in sidereal mode point the OTA to a star on the meridian at about 0 degrees declination Orient the cross hairs to north south east and west If you have trouble orienting yourself to N S E and W try this whilst viewing the star in the cross hairs gently put a little pressure with your finger on the back top end of the tube and watch the star try to move This will help you orient yourself to the north south direction Re center the star Sit back and watch it drift for a few minutes If the star drifts north the polar axis is too far to the west If it drifts south the polar axis is too far to the east See diagram below l i North West East Face of mount y ZN 1 Point the system north 2 If star drifts north move east 3 If star drifts south move west While you are watching the drift disregard the periodic error east and west movement of the star We are only interested in the direction of the north or south drift Make the necessary adjustments in azimuth re center the star and allow to drift again Repeat the procedure until there is no north or south drift The drift accuracy needed will be dependant upon the maximum exposure length of time you intend to photograph For ex
8. enter pivot shoulder screw under the U nut needs to be removed in order to remove the black adapter plate It needs to be re inserted into the center hole of the female rocker when re assembling To accomplish this the lead screw will need to be moved out of the way Using an Allen wrench loosen the shaft collar set screw and loosen the locking nut Turn the lead screw handle until you have free access to the center hole It will be necessary to completely remove the U nut in order to access the center pivot shoulder bolt The small Allen wrench has been provided to loosen the shaft collar 3 Removing the Female Rocker from the Adapter Plate Next remove the female rocker base from the black adapter plate by removing the ratchet handles To do this lift up on the handle and turn just to break loose Then remove the top center socket head screw in the handle It will come out with a spring Now lift off the handle You can then unscrew the inner part of the ratchet The female rocker will then lift off the adapter plate You can now secure the adapter plate to your pier Be sure to orient the slotted hole to the north 4 Reassembling the RA and Female Rocker Place the rocker on top of the adapter plate Make sure the azimuth bar fits into the slotted hole on the top side of the adapter plate Very slightly tighten the shoulder bolt using an Allen wrench Take care not to over tighten the shoulder bolt Just bring
9. he system Refer to Part 2 for declination worm adjustment 2 6 5 Step 3 Loosen and remove the two socket head cap screw s 5 that secure the motors gear box to the worm bearing block Step 4 Carefully remove the motor taking notice how the coupling 6 disassembles Set it aside for the moment Step 5 Now is a good time to inspect your current mesh Using your thumbs to turn the worm rotate it a few revolutions to get the feel of it Are there rough spots Is there binding Rock your RA axis east to west to get a feel for the current backlash back lash is the movement allowed within the gear to worm mesh Step 6 Locate the two worm adjustment screws 2 Back them off slightly and then screw them in to re contact the worm assembly Do not apply pressure Stop turning when you first feel contact Step 7 Locate the two socket head caps screws lock down screws 1 With the same Allen wrench that is used for your clutches loosen the right side first then gently snug it back down Then do the same to the left side lock down screw We don t want them so tight as to prevent adjustments and at the same time we want them secure Important Don t remove both screws with the OTA and counterweights assembled There is a lot of pressure on the worm It holds your system in place Removing the worm or its lock down screws will cause your system to crash Step 8 If your mesh seemed tight you need to loosen it If the
10. ine of the teeth section iCenter line of gear eg 4 25 Gear Key Stock 25 offest from cent When replacing the worm assembly first insure that any brass shims that may have been originally used under the worm assembly are replaced back to the same side that they came from This is important because the may vary in thickness These shims precisely position the center line of the gear to the center line of the worm as viewed from a horizontal position In other words the shims lift the worm to the exact horizontal center line position Back out the worm adjustment screws This allows for easier reinstallation of the worm assembly Once the worm assembly is in place and the lock down screws are in place to finger tightness rough adjustments can be made with the key stock From a vertical position insert the key stock flush against the bearing with it s right upper corner just touching the actual gear See diagram You may have to tip tilt the worm assembly to achieve this rough position Do this by adjusting the worm adjustment screws This method will get you into the ball park with regards to the tip tilt angular position of the worm to gear Ideally after the final adjustments are completed the key stock will just barely fit into place You can now proceed with steps 1 through steps 10 for final adjustments Worm lateral adjustment Your worm assembly consists of two bearing b
11. it into contact and stop If you over tighten the shoulder bolt you will not be able to turn the azimuth knob during polar alignment The shoulder bolt should be in contact and yet still allow the rocker assembly to rotate with just a slight amount of drag Now re secure the altitude lead screw assembly in the reverse order that you removed it Do not over tighten the collar to the point that the knob is difficult to turn A little backlash will not affect anything An additional pair of ratchets has been sent so that you can use them for the altitude lock downs A few drops of 3 In One oil on the handles will help prevent corrosion Your mount was sent using only nuts and washers for the altitude lock downs The next step is to secure the azimuth lock down ratchet knobs These knobs also secure the rocker to the adapter plate To use just loosen the ratchets and turn the azimuth knob for polar alignment adjustments To loosen the ratchets lift the handle and turn it to the desired position Drop it down to engage the ratchet 5 Securing Adapter Plate to your Pier Top The adapter plate needs to be secured it to your pier or tripod by whatever means necessary as long as it is good and secure Make sure that any bolt heads are under the top surface of the plate Also be sure to orient the slotted hole in the adapter plate to your north position You should try to get within a few degrees of pointing north Helpful Suggestion Drill and co
12. locks and one cross piece The larger bearing block accommodates the motor assembly The opposite end is smaller in size The smaller bearing block has been modified so that any lateral play of the worm between the two bearings can be adjusted out Look at the outside end of the small bearing block You ll see three very small set screws at 120 degrees apart that are around the outside bearing race These set screws are 1 8 long 6 32 s With an Allen wrench carefully snug the set screws down equally until there is no lateral play of the worm If you feel roughness while rotating the worm slightly back off the set screws Removal of main gear The main gear can be removed from either the RA or declination axis for cleaning or re lubricating When re lubricating a gear keep in mind that the same type of lubrication should be used Mixing of different lubes can result in poor performance of lubrication Mixing can occur if there is residual lubrication left on the worm or elsewhere F 1 Remove dec assembly 2 Remove clutch levers pictures show star knobs levers are currently used 3 Remove cover plate 4 Back off worm adjustment screws 5 Loosen worm lock down screws 6 Drop down worm so that it clears the gear not shown in picture 7 Remove inner 4 socket head cap screws 8 Do not let plate fall off Set aside 9 Carefully lift out gear 10 Perform necessary maintenance and reverse order for
13. m so that you can slide the OTA forward or back Take care in doing this as the OTA could slip loose and fall Move the OTA back or forth until you achieve balance After achieving balance tighten the DA s so that the OTA can not slide in either direction Please note that your Losmandy male dovetail will have been supplied with a safety thumb screw which should be used as a safety precaution You may find that you need to add a supplemental weight system when attempting to balance some Schmidt Cassegrains When taking photographs this balance process should be performed and fine tuned for the specific area of interest in the sky SECTION 3 POLAR ALIGNMENT Described below is a simplified version of the star drift method It is among the most accurate methods known for precision polar alignment An illuminated ocular will be necessary Drift alignment time can be reduced significantly by the use of a Mountain Instruments polar alignment scope You will need the system running in order to polar align Refer to Gemini manual for proper start up The adjustment of the polar axis is accomplished with the azimuth and altitude lock down handles and knobs It is easier i to practice with these adjustments in the daylight so that you become familiar with rotational directions 3 1 Azimuth Star Drift IMPORTANT Keep the alt and az ENT handles turned in or remove the handle not the inner barrel when not in use If not the saddle pl
14. mesh seemed loose you need to tighten it Let s assume it was tight Put the Allen wrench back into the right side socket head cap screw lock down screw and leave it there With one hand slightly loosen that lockdown screw and with the other hand turn the right side adjustment screw outwards counter clockwise about 1 32 of a turn Turning the adjustment screw 1 32 actually moves the worm by about 0 001 one thousandth of an inch The point is that it doesn t take much to make adjustments Step 9 With one hand using your thumb and forefinger apply pressure to the bearing blocks forcing the worm assembly against the adjustment screws 2 and slightly re tighten the right hand lock down screw while applying the pressure against the adjustment screws Move the Allen wrench to the left side lock down screw and slightly tighten Now move it back to the right side and tighten more Finish by tightening down the left hand side Step 10 Repeat step 5 Freewheel the worm a few revolutions Does it feel different than the first time If not repeat the steps If you went too far reverse the adjustment screw direction Don t be surprised if it takes numerous times to get it right Even with a lot of practice here at Mountain Instruments it can still take us 15 20 minutes to adjust a system properly There is always controversy as to how tight the mesh should be We have found that the best performance is achieved when there is a slight
15. n each axis to lock clutches SECTION 2 BALANCING THE OTA Whenever the mount and OTA are assembled after transportation or storage the system should always be balanced Accurate tracking depends on proper balance 2 1 RA Balance Prior to balancing the RA or dec axis attach any cameras finders oculars or guide scopes that you plan to use during your session Loosen the RA clutch screws and position the OTA to either the east or west side of the mount Use caution during this procedure due to the system being initially unbalanced Then determine if the OTA or the counterweight side is heavier Depending on which side is heavier adjust the counterweight up or down the shaft as necessary to achieve balance in RA Once balance is achieved hand tighten the counter weight locking nuts into place Do not use tools for this as it will wear the threads on the locking nuts You will probably find that a slight imbalance to the east side will give the best tracking i e the east side should be slightly heavier This will help to take up any backlash between the gear and the worm 2 2 DEC Balance Tighten the RA clutch screws with the declination axis in a horizontal position Loosen the dec clutch knobs and position the OTA in a horizontal position As with the RA be careful not to let go of the OTA When out of balance it will fall Your system was purchased with two preinstalled female dovetail assembly DA s Slightly loosen the
16. polar aligned The orientation is referenced from the face of the mount i e the part with the electronics on it which is facing north The smaller end of the polar assembly faces south Thus if you are facing the electronics which puts north behind you you are facing south In that position your right hand is west and your left is east SECTION 1 SETTING UP THE MOUNT 1 1 Mounting the Base to the Pier After assembling the pier the first step in setting up your MI 250 Go To is to secure the RA assembly to the pier Begin by removing the three bolts from the lower black anodized RA base assembly These are the three bolts that will secure the base to the top of the pier The pier has been marked with a with a north arrow Turn the pier so that the arrow points north prior to mounting the RA assembly The picture shows the Mountain Instruments MI 8P heavy duty pier Place the mount into the top of the pier and line up the holes Snug down the three bolts Do not force them to the point of stripping the threads 1 2 Attaching the Dec Assembly The next step is to attach the German declination assembly to the RA assembly The dec assembly is top heavy so before attaching the dec assembly tighten the RA clutch screws See the next section for clutch adjustment Be sure to wipe off any debris that might be on the face of the polar shaft or the flat surface of the dec assembly prior to assembly Locate the 1 center hole on the dec a
17. ssembly This hole is provided to register the center of the dec assembly onto the center stud of the polar shaft It also steadies the dec assembly while securing the dec bolts Do not rely on the center stud to hold the dec in place while fastening the dec bolts Place the dec assembly onto the center stud and screw in the dec bolts Insert each and partially screw down all the bolts before tightening any one bolt Again take care not to over tighten any of the bolts as this will strip the threads tighten just enough to provide a snug fit After securing the dec bolts screw the counter weight shaft into the dec assembly Hand tighten the shaft to the point where there is no play in it In order to add the counter weights to the shaft first loosen the primary RA clutch adjustment screws refer to next page and rotate the dec axis to a horizontal position Screw one of the weight locking nuts onto the counter weight shaft Place one or two counter weights onto the shaft and thread on the other locking nut Note that the counter weight itself is not threaded Return the dec axis to the counter weight down position The OTA can now be attached to the saddle plate 1 3 RA and DEC Clutch Adjustment Procedure for Both Axes Once the OTA and counter weights are in place the slip ciutene should tightened to the point so that there can be no manual movement for go to use There are two clutch levers on each axis Tighten both knobs o
18. unter bore three holes for use with a 5 16 18 socket head cap screw Counter bore half way through the plate This is much easier than a hex head bolt Washer Geometry Take a close look at a stainless steel washer You will see that on one side of the washer the edges are beveled or rounded On the other side of the washer the edges are square and sharp When using stainless steel washers on powder coated surfaces which most of the MI 250 is place the beveled side of the washer against the powder coating It will help prevent scratching the paint WASHER TOP VIEW ROUNDED CORNERS WASHER SIDE VIEW h wane CORNERS For easier installation or removal 1 Remove top center Allen screw 2 Remove barrel and spring from handle 3 Screw barrel onto post 4 Replace spring and screw with handle
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