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Meade StarPro AZ Mount (70-102mm Refractor Line) -- "Under the Hood"

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#26 Veridian

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Posted 18 June 2021 - 02:45 AM

  Before getting into the problems with the roundnut, here are some photos of the altitude control during dissassembly that should have been included earlier.

 

  The worm's ring-gear did not readily slip off of the axle/driveshaft on the 90mm as it easily did on the 70mm. It had to be coaxed off with a gear puller. Before fitting the puller to the ring-gear and axle, an allen screw was threaded into central hole for the axle's clutch knob screw. This is to protect the starting threads in the bore from being damaged by the puller's shaft tip (red dot)

   When pulling off the ring-gear, the worm was turned with the slow-motion control to prevent the teeth from pinching and binding. The puller's 2 jaws and its shaft were carefully centered, the puller's shaft then only needed turning with my thumb and forefinger, to bring it off the axle.

   Once the ring-gear was off, I saw the problem. Somehow, during assembly at the factory, it appears that a pliers was used on the axle at the bearing surface where the ring-gear turns. This left a series of burrs and gouges that were galling and jamming the inner diameter, bearing surface of the ring-gear. Why a pliers would have been used on this part and in this location is a mystery. 

   The bearing surface on the axle was dressed with a small, fine tooth, mill file (pictured in an earlier post). Laying the file flat and level on the surface, the axle was turned in place on the side-arm with one hand, while applying even, light pressure on the top side of the file with one finger of the other hand. Doing it in this manner prevents the file from rocking and gives better control than were the hub/axle and file to be held in the hands. In an upcoming photo, the damaged axle will be seen.

Attached Thumbnails

  • StarPro AZ; removing a tight ring-gear.jpg

Edited by Veridian, 18 June 2021 - 09:30 PM.

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#27 Veridian

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Posted 18 June 2021 - 03:25 AM

  Here again, is the altitude control, sans knob, hood, outer pressure plate ("pork pie hat"), 2 nylon washers and ring-gear. My modified "1/16th" allen wrench is shown inserted into one of the 3 (M3) set-screws of the roundnut, which functions as the fixed, inner pressure plate of the clutch.

   The allen screw seen in the central hole of the axle (for the clutch knob) was placed there to prevent thread damage, when using a gear puller to remove the ring-gear (described in post directly above).

 

   When removing the 3 (M3) set-screws I made certain the 3 were squared as they emerged from their holes. In other words, the amount of screw shaft seen equals its diameter. The set-screws are then fully above and off of the threads on the axle beneath. This helps ensure the threads on the axle shaft beneath are not damaged by a set-screw dragging on a thread, when unscrewing the nut. In a situation where a nut has slipped and the set-screws dragged on the threads, having the set-screws well screwed out gives a place for the metal chips to go, when unscrewing the nut, instead of clogging and jamming the threads  [An example of this will later be seen in a photo of the damaged axle for the 70mm.]

Attached Thumbnails

  • StarPro AZ; altitude sans clutch free parts.jpg

Edited by Veridian, 18 June 2021 - 09:32 PM.

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#28 Veridian

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Posted 18 June 2021 - 03:39 AM

   The altitude control with the 2 hole, roundnut removed.

   Without the clutch parts, only the worm block and the hub with its axle/driveshaft now remain in the upper side-arm casting. The hub and axle unit slips out from the other side of the casting. 

Attached Thumbnails

  • StarPro AZ; altitude cntrl. w ringnut removed.jpg

Edited by Veridian, 18 June 2021 - 09:33 PM.

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#29 Veridian

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Posted 18 June 2021 - 03:58 AM

  The hub and axle unit with the 2 hole roundnut are pictured here. Dimensions for the roundnut are printed on the paper in the photo, but in case these are difficult to read, they are written here:

 

Roundnut Dimensions

 

37,5mm OD (~1.5 in.)

16mm ID      (5/8 in.)

5mm Thick. (3/16 in.)

thread pitch: 1,0mm  (almost SAE 28 tpi, but not quite)

4 threads total

 

Set-screw dimensions (3 @ 120°)

 

3mm dia. (M3) x 10mm long

thread pitch: 0,5mm 

1/16th in. allen socket

 

 

Attached Thumbnails

  • StarPro AZ; altitude hub & axle; ringnut.jpg

Edited by Veridian, 18 June 2021 - 09:35 PM.

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#30 Veridian

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Posted 18 June 2021 - 04:33 AM

  In the photo above and from top to bottom, the green dot denotes the 14mm dia. axle/driveshaft bearing surface. This is where the worm's ring-gear and the "pork pie hat", outer pressure plate ride. A close look, just below and to the right of the green dot, will show the damage to the bearing surface during assembly at the factory. This is where the ring-gear rides.

[These parts are from the 90mm mount]

  The yellow dot shows the 16mm threading on the axle for the 2 hole, roundnut. Immediately to the right of this yellow dot is where one of the 3 set-screws had been tightened into the thread to pinch it and set the nut. It appears as a shiny dot, here. This is normal for set-screws with a flat tip and which is what these are. In my opinion, a tapered, "cone point" tip may have been a better choice for these set-screws. [These are available from McMaster-Carr in 8mm length, but are sold in package quantity (25 in SS and 50 in black oxide).  Perhaps I'll try a good hardware, or auto parts store and they may have these in a cone point and sold per piece.]

   In this case, the set-screws were just beginning to loosen (they were barely snug), but the round nut had not yet been loosened enough to turn on the threads. Had it loosened any further, the 3 set-screws would have been dragged through the threading and gouged it out as the nut was forcing itself to unthread. This is what happened on my 70mm. Later, a photo will be taken and posted that shows the damage.  

 

   The orange dot denotes the 20mm dia. hub bearing surface that rides in the bore of the side-arm casting.

    

   The red dot is, of course, the roundnut* itself and just to the left of the red dot is one of the 3  set-screws. Here, this view shows the set-screw turned out and "squared".

 

   The tool in the background is a metric thread gauge.

 

 

 *  From the beginning, what I have been calling the "roundnut" is also known more correctly as a "pin spanner nut". Although, most spanner nuts have slots around their periphery for a hook/claw spanner wrench to engage. In the trade and when at the parts counter, to distinguish the two types, avoid confusion and for brevity, I would usually call the type of spanner nut used here a "round nut". 


Edited by Veridian, 19 June 2021 - 02:13 AM.

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#31 Veridian

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Posted 18 June 2021 - 06:44 PM

  There were two indications that should have warned me something was amiss with the altitude control on my 70mm mount and I ought to have paid closer attention. Had I known better, I would have immediately stopped operating the telescope and investigated the problem.

 

These are the two warning signs to watch for:

 

1.  Slow-motion control is momentarily lost when the clutch is engaged (clutch knob tightened).

 

2.  Free swing of the tube occasionally going from smooth and free to grabby and stiff, with the clutch  disengaged (clutch knob loosened).

 

   This was noticed a couple of days before going "under the hood" and, at the time, I did not think too much about it. I would just cycle the clutch release knob a couple of times. It would then feel ok, for a while, as the free swing smoothened out. With the clutch then re-tightened, slow-motion control would usually return. What I did not know, at this time, is that these were the two warning signs that the clutch's inner pressure plate - the roundnut - was loosening on the axle and beginning to unthread itself.

 

    The way this design works, for the positive action of the slow-motion control worm to transfer its torque to the worm ring gear and on through the axle to the telescope, is the clutch knob must be tightened to press the parts together and create enough friction to stop their free rotation. The worm ring gear that normally free spins on the axle with the clutch loosened - is now pinched between the clutch's inner and outer pressure plates when the clutch knob is tightened. With the clutch knob tight and as the slow-motion control is turned, all of the parts on this axle then turn as one unit.

   The two anchor points for holding and maintaining this pressure and friction are the (M6) 6mm × 1,0mm threads on the clutch control knob (matched by the internal threads in the central axle) and the 4 threads on the 16mm ID of the roundnut. The 3 (M3) set-screws are all that keep the roundnut tight on the axle. That's it, , just the 4 internal threads of the roundnut and these 3 set screws to keep it in place, as it holds the pressure of everything else pushing up against it! 

   This design works fine from the outside end of the axle where the worm assembly engages and applies its torque, as there is only minimal lateral leverage. However, when the lateral torque from the telescope tube side is applied (the hub), we have an altogether different situation.

    

    Earlier, I had stated in post #23 that I was unable to find any mention of loosening the clutches before putting the telescope into free scan motion. After re-reading the instruction manual a couple of more times, I did find on page 5 where it states: "To move the telescope in the vertical direction (altitude), slightly loosen the vertical lock knob (26) and use the ota body to make coarse adjustments up and down." It states much the same for the horizontal (azimuth) motion. The problem I see here is that perhaps the instruction manual should instead read: "fully loosen", instead of "slightly loosen".    

 

   What I believe the cause for the roundnut to loosen is when not fully loosening the clutch knob, the leveraged torque of the telescope tube is then applied to the inside surface (hub side) of the roundnut, when the tube is moved up and down. This leveraged up and down motion can then place a significant turning action upon the hub side of the roundnut and eventualy loosen the 3 set-screws, thus allowing it to break free and turn on the axle.


Edited by Veridian, 18 June 2021 - 11:49 PM.

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#32 Veridian

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Posted 19 June 2021 - 12:39 AM

  This photo shows the damage to the threads on the altitude control axle caused by the 3 (M3) set-screws in the roundnut, as it was trying to unthread itself. This happened during the up and down motion of the telescope in the free swing mode and with the clutch slightly loosened.

   The roundnut turning and gouging the threads translated into the course, grabby slipping and stalling that was felt during the free swing mode described in the posts above. With the clutch knob tightened (clutch engaged), the nut should not rotate on the axle when the slow-motion control was turned. But, it was. As the roundnut was now rotating independent of the axle it could no longer function as the fixed pressure plate on the axle. The worm was unable to make a continuous and steady transfer of its motion on through the axle to the telescope on the hub. This is why occasional, momentary loss of slow-motion control was happening with the clutch engaged. Without a video, this is a bit difficult to find the right words to describe,  so I hope the way I am writing it is understandable.

   

   The flat, shiny spot on the threads is where one of the loosening set-screws was being dragged along. This same damage was found at the other two set-screw locations around the threading.

   While I think the axle is still serviceable, with the round-nut's already, quite limited number of only 4 threads (16mm x 1,0mm), losing this thread contact area certainly will not help the round-nut maintain its fixed, pressure plate position and function on the axle. I have to keep in mind that its fixed position actually relies upon the 3 set-screws inside the round-nut. I am inclined to think "cone point" tips would give a firmer, tighter bite on the axle. This is why I am leaning toward replacing these flat tip screws with metric (M3) "cone points". 

 

   In the second photo is another view of the round-nut in close-up. The four, inner diameter threads  (16mm x 1,0mm) of the round-nut can be seen, as well as the "flat point" of one of the 3 set-screw's tips. 

   Relying upon this round-nut with its 3 set-screws to function as a fixed pressure plate is not the best idea. Instead, a more substantial and traditional design would have been using a machined, internally splined, flat disc of about 5mm in thickness and with matching, machined splines on the axle. Of course, this would have added additional expense to its manufacture. As it is, this single part may well be the "Achilles Heel" to an otherwise excellent mount. Somehow, I suspect that the fingerprints of an accountant might be found on the final design blueprints.

 

Next, how I plan to get around this problem.

Attached Thumbnails

  • StarPro AZ; axle thread damage.jpg
  • StarPro AZ; roundnut (pin spanner nut).jpg

Edited by Veridian, 19 June 2021 - 02:30 AM.

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#33 Veridian

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Posted 20 June 2021 - 07:57 PM

  Working with what I have here, there are not many options to correct the problem of the roundnut (inner pressure plate) loosening and turning on the axle. I came up with three to consider.

 

1. Assemble the parts as they are and continue to rely upon the 3 set-screws to keep the roundnut fixed and tight upon the axle.

2. Backing off the set-scews and tightening the roundnut enough to remove the lateral side play of the axle and hub in the side-arm and hope it remains stationary and fixed to the axle by thread tension alone.

3. Applying threadlocker compound - e.g., Loctite or Permatex - to the threading on the roundnut and axle. 

 

   The first option only continues the problem and risks further damage to the threads on the axle. The one thing I do NOT want to do is to re-tighten the 3 set-screws, should I find them loose again. Without knowing the exact, initial contact points on the axle where the set-screws were originally screwed into, I would only crush more of the relatively soft, aluminum axle threads and cause more damage. I need to remember that the axle is turned from the one piece, aluminum hub casting.

 

   As I see it, there is simply no way these 3 set-screws can withstand the repeated forces placed against them and remain tight. The "fore and aft" pressure applied against them from loosening and tightening the clutch and then the constant torque force of the worm gear during slow-motion action is just too much for the tiny contact area of 3 set-screws. Add to this the tube's up and down (especially vertical) motion and the "to and fro" torque and friction this applies to the inside surface of the roundnut. As is, the repeated "to & fro" and "fore & aft" forces being directed at the roundnut are bound to loosen the set-screws and then the roundnut. This is the weak link in the chain of parts that make up the altitude control drive train.

 

   The second option is being tried on both mounts (the 70 and 90) and so far, within one viewing session, the adjustment of the roundnut on the axle is lost and pauses begin to happen during directional changes in slow-motion control. In other words, with clutch engaged (tight) and when it should be fixed to the axle the roundnut is loosening and turning on the axle as the action from the worm and ring-gear are engaged. Even with the clutch fully disengaged (loosened), with the roundnut adjusted to remove all sideplay of the hub in the side-arm, there is still enough friction against the inside surface of the roundnut to create an unthreading action on the nut. This is particularly the case when the tube is being elevated in the vertical direction of free swing motion.

 

   The third option may be the only one that has a good chance to work. Threadlocking compound could keep the nut tight on the axle, once properly adjusted. Loctite 242 Blue and Permatex Blue are both rated as medium strength and may be enough. Although, from my experience, these compounds are designed to set and harden best in an anaerobic situation. In order for optimum performance to be realized, once the Loctite is applied, the fastener's thread surfaces should be tightened enough to squeeze out the air (oxygen) between the threads. In this situation, though, the roundnut's threads are not able to be tightened enough to reach an optimum anaerobic condition. Anyway, I thought to give it a try.

 

   Before Loctite application, I made certain the threads of both the roundnut and axle were thoroughly cleaned of any grease and completely dry. I shook the vial well, applied a drop to both thread surfaces, made the adjustment and waited a full 24 hours for it to set, dry and harden. It didn't. After finding that it again loosened, when removing the round-nut I found the Loctite applied to the threads the day before had not even begun to set and harden. It was still wet.

   What I have been reading in some other mechanical theme forums is that for the threadlocker to work right, it must be fresh and that it has a shelf life of less than 2 years. Then again, others have written that Loctite they had for many years is still used with good results. At this time, both vials I have of the medium strength, blue Loctite and Permatex threadlocker are quite old and have been in the toolbox for 20 years, or more. I assumed this to be the reason the compound would not dry, set up and harden in the 24 hours as it should. I don't know why mine did not set up. Perhaps it was because the round-nut could not be tightened enough to create the anaerobic situation it requires for proper set up. So, another attempt will be made when what I have has been replaced with fresh Loctite. I also need a method to get the roundnut's threads tighter during the curing time.  

 

Adjusting and Tightening the Round-Nut: To get around not being able to fully tighten the roundnut's threads on my first attempt, I may try adjusting the nut, while slipping a feeler gauge blade between the nut and the inner, *nylon washer on the side-arm (seen in photo above) and then tightening the nut just enough against the inserted blade to reach an anaerobic condition.   

   While adjusting and tightening the round-nut, for better control and leverage I use the makeshift pins fashioned from two finishing nails placed in the nut's two holes. A few attempts with different thicknesses of blades will need to be tried to get the best adjustment and I'll start with either .006" or .008" blades (0,15mm and 0,20mm). The adjustment aim is to have the nut tighten at the point where the set-screws line up with the pre-existing flats on the axle threads, or just off to the right of the flats. More on this below.

   Once the correct adjustment is found and the nut well snugged up against the blade between it and the "nylon" washer, I'll then wait the full 24 hours to see if the threadlocker compound fully sets up and hardens. Afterwards, I can gently work the feeler gauge blade out from between the nut and nylon washer. 

   The plan is that If the medium strength blue Loctite 242 now fully sets and hardens, the round-nut should be tight enough on the axle threads to resist my being able to loosen it with thumb and fingers, using the pins in the round-nut's 2 holes for control and leverage, but without forcing it. With luck, there won't be any side shake of the hub in the side-arm and maybe there will even be a slight drag on the tube's vertical, free motion.

   There is a temptation to use Loctite Red (271) High Strength here, but I am resisting this temptation. Should I want to change the roundnut adjustment, the Loctite Red 271 usually has to be heated (500°F) to melt the compound and allow for the nut to be loosened.  Applying heat to the nut will most likely ruin the nylon friction washer directly behind and in contact with it.

Using Loctite 271 Red is my last resort. Should the Loctite 242 Blue not work out then I'll find some replacement, "nylon" washers somewhere and go with it.

 

    Set-Screws (flat point vs. cone point): If able to reasonably secure the round-nut with Loctite, I am leaning towards replacing the original, "flat point" set-screws with M3 "cone point" set-screws. These are designed for more permanent and secure situations. Also, instead of crushing the thread, like a flat point, when tightened, the cone point is forced between the threads and not down on top of them.

   If, as planned, the round-nut is sufficiently tight with using the 242 Loctite alone, I may want to include additional security with 3 "cone point" set-screws. Having adjusted the round-nut with the set-screw holes aligned just to the right of the pre-existing flats on the axle threads, when tightening the set-screws, the cone points will bore in between the threads just behind these 3 flats. The flats should provide a stop for the points, adding a little more security in helping to resist any unthreading force on the round-nut. 

 

   Were there more axle threads exposed on the outer side of the roundnut, I would like to try threading a low profile, spanner nut up against the roundnut and to act as a locknut. But, there are not enough exposed threads here and then a recess would need to be machined on the inside surface of the worm ring-gear to accomodate the profile of the locknut. Of course, this would then reduce the contact area of friction for the ring-gear on the roundnut. It's always something.

    

   What I would really like to see happen is for Meade to replace this "round-nut on the axle as a pressure plate" function and to redesign it with a proper and traditional splined friction plate and matching, splined axle - as briefly described in the post above (#32). It would be great if a redesigned hub, axle and pressure plate were to be interchangeable with the existing mounts and then made available as an upgrade.

   Of course, a wish like this may be about as fruitful as standing in Death Valley, with both hands out and waiting for my wishes to fill one hand, for the other to fill with rain and see which one fills first. Oh well, in a perfect world, the engineers would have the final say on the blueprints and not the accountants.

 

 *  I have been referring to the white, plastic washers as nylon. They look and feel like nylon, but may well be another plastic, e.g., ptfe, teflon, delrin, etc.

 

Getting back to the azimuth controls is next and I'll try to keep the following explanations more brief.


Edited by Veridian, 21 June 2021 - 05:03 PM.

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#34 biz

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Posted 21 June 2021 - 02:14 PM

  Working with what I have here, there are not many options to correct the problem of the roundnut (inner pressure plate) loosening and turning on the axle. I came up with three to consider.

 

1. Assemble the parts as they are and continue to rely upon the 3 set-screws to keep the roundnut fixed and tight upon the axle.

2. Backing off the set-scews and tightening the roundnut enough to remove the lateral side play of the axle and hub in the side-arm and hope it remains stationary and fixed to the axle by thread tension alone.

3. Applying threadlocker compound - e.g., Loctite or Permatex - to the threading on the roundnut and axle. 

 

   The first option only continues the problem and risks further damage to the threads on the axle. The one thing I do NOT want to do is to re-tighten the 3 set-screws, should I find them loose again. Without knowing the exact, initial contact points on the axle where the set-screws were originally screwed into, I would only crush more of the relatively soft, aluminum axle threads and cause more damage. I need to remember that the axle is turned from the one piece, aluminum hub casting.

 

   As I see it, there is simply no way these 3 set-screws can withstand the repeated forces placed against them and remain tight. The "fore and aft" pressure applied against them from loosening and tightening the clutch and then the constant torque force of the worm gear during slow-motion action is just too much for the tiny contact area of 3 set-screws. Add to this the tube's up and down (especially vertical) motion and the "to and fro" torque and friction this applies to the inside surface of the roundnut. As is, the repeated "to & fro" and "fore & aft" forces being directed at the roundnut are bound to loosen the set-screws and then the roundnut. This is the weak link in the chain of parts that make up the altitude control drive train.

 

   The second option is being tried on both mounts (the 70 and 90) and so far, within one viewing session, the adjustment of the roundnut on the axle is lost and pauses begin to happen during directional changes in slow-motion control. In other words, with clutch engaged (tight) and when it should be fixed to the axle the roundnut is loosening and turning on the axle as the action from the worm and ring-gear are engaged. Even with the clutch fully disengaged (loosened), with the roundnut adjusted to remove all sideplay of the hub in the side-arm, there is still enough friction against the inside surface of the roundnut to create an unthreading action on the nut. This is particularly the case when the tube is being elevated in the vertical direction of free swing motion.

 

   The third option may be the only one that has a good chance to work. Threadlocking compound could keep the nut tight on the axle, once properly adjusted. Loctite 242 Blue and Permatex Blue are both rated as medium strength and may be enough. Although, from my experience, these compounds are designed to set and harden best in an anaerobic situation. In order for optimum performance to be realized, once the Loctite is applied, the fastener's thread surfaces should be tightened enough to squeeze out the air (oxygen) between the threads. In this situation, though, the roundnut's threads are not able to be tightened enough to reach an optimum anaerobic condition. Anyway, I thought to give it a try.

 

   Before Loctite application, I made certain the threads of both the roundnut and axle were thoroughly cleaned of any grease and completely dry. I shook the vial well, applied a drop to both thread surfaces, made the adjustment and waited a full 24 hours for it to set, dry and harden. It didn't. After it again loosened, when removing the round-nut I found the Loctite applied to the threads had not even begun to set and harden. It was still wet.

   At this time, both vials I have of the medium strength, blue Loctite and Permatex threadlocker are too old and the compound will not set, dry and harden as it should. What I have been reading is that for threadlocker to work right, it must be fresh. It has a shelf life of less than 2 years and mine has been in the toolbox for much, much longer. So, another attempt will be made when what I have has been replaced with fresh Loctite. I also need a method to get the roundnut's threads tighter during the curing time.  

 

Adjusting and Tightening the Round-Nut: To get around not being able to fully tighten the roundnut's threads on my first attempt, I may try adjusting the nut, while slipping a feeler gauge blade between the nut and the inner, *nylon washer on the side-arm (seen in photo above) and then tightening the nut just enough against the inserted blade to reach an anaerobic condition. While adjusting and tightening the round-nut, for control and leverage I use the makeshift pins fashioned from two finishing nails placed in the nut's two holes. A few attempts with different thicknesses of blades will need to be tried to get the best adjustment and I'll start with either .006" or .008" blades. The adjustment aim is to have the nut tighten at the point where the set-screws line up with the pre-existing flats on the axle threads, or just off to the right of the flats. More on this below.

   Once the correct adjustment is found and the nut well snugged up against the blade between it and the nylon washer, I'll wait for the threadlocker compound to fully set and harden (about 24 hours). Then, I can gently work the feeler gauge blade out from between the nut and nylon washer. 

   The plan is that If the medium strength blue Loctite 242 now fully sets and hardens, the round-nut should be tight enough on the axle threads to resist my being able to loosen it with thumb and fingers, using the pins in the round-nut's 2 holes for leverage, but without forcing it. With luck, there won't be any side shake of the hub in the side-arm and maybe there will even be a slight drag on the tube's vertical, free motion.

   There is a temptation to use Loctite Red (271) High Strength here, but I am resisting this temptation. Should I want to change the roundnut adjustment, the Loctite Red 271 usually has to be heated (500°F) to melt the compound and allow for the nut to be loosened.  Applying heat to the nut will most likely ruin the nylon friction washer directly behind and in contact with it.

Using Loctite 271 Red is my last resort. Should the Loctite 242 Blue not work out then I'll find some replacement, nylon washers somewhere and go with it.

 

    Set-Screws (flat point vs. cone point): If able to reasonably secure the round-nut with Loctite, I am leaning towards replacing the original, "flat point" set-screws with M3 "cone point" set-screws. These are designed for more permanent and secure situations. Also, instead of crushing the thread, like a flat point, when tightened, the cone point is forced between the threads and not down on top of them.

   If, as planned, the round-nut is sufficiently tight with using the 242 Loctite alone, I may want to include additional security with 3 "cone point" set-screws. Having adjusted the round-nut with the set-screw holes aligned just to the right of the pre-existing flats on the axle threads, when tightening the set-screws, the cone points will bore in between the threads just behind these 3 flats. The flats should provide a stop for the points, adding a little more security in helping to resist any unthreading force on the round-nut. 

 

   Were there more axle threads exposed on the outer side of the roundnut, I would like to try threading a low profile, spanner nut up against the roundnut and to act as a locknut. But, there are not enough exposed threads here and then a recess would need to be machined on the inside surface of the worm ring-gear to accomodate the profile of the locknut. Of course, this would then reduce the contact area of friction for the ring-gear on the roundnut. It's always something.

    

   What I would really like to see happen is for Meade to replace this "round-nut on the axle as a pressure plate" function and to redesign it with a proper and traditional splined friction plate and matching, splined axle - as briefly described in the post above (#32). It would be great if a redesigned hub, axle and pressure plate were to be interchangeable with the existing mounts and then made available as an upgrade.

   Of course, a wish like this may be about as fruitful as standing in Death Valley, with both hands out and waiting for my wishes to fill one hand, for the other to fill with rain and see which one fills first. Oh well, in a perfect world, the engineers would have the final say on the blueprints and not the accountants.

 

 *  I have been referring to the white, plastic washers as nylon. They look and feel like nylon, but may well be another plastic, e.g., ptfe, teflon, delrin, etc.

 

Getting back to the azimuth controls is next and I'll try to keep the following explanations more brief.

Mark, your comment that loctite only has a shelf life of two years is interesting. I store several bottles of this in a small fridge in my workshop and this has been for several years . I build a lot of telescope items on my lathe and mill and use loctite quite often. All of which has come from the fridge has been reliable.  Maybe you could try this.

keeping the items you are glueing ,clean, is important.

cheers

Graham


Edited by biz, 21 June 2021 - 02:17 PM.

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#35 Veridian

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Posted 21 June 2021 - 04:31 PM

Mark, your comment that loctite only has a shelf life of two years is interesting. I store several bottles of this in a small fridge in my workshop and this has been for several years . I build a lot of telescope items on my lathe and mill and use loctite quite often. All of which has come from the fridge has been reliable.  Maybe you could try this.

keeping the items you are glueing ,clean, is important.

cheers

Graham

   Graham (biz), thanks for this. I will go back and edit the post.

   I had read where some people have been keeping theirs in the fridge and then some others commented this should not be done. Your credible experience supports the former.

   After waiting the full 24 hours for the Blue 242 to set and harden and then finding it had not, I assumed it was because the vial I have here is quite old (20+ years?). This has not happened before, but then the nut in this circumstance was not fully tight either.

   I could not find any mention on the Loctite website where it stated the fastener had to be fully tightened to achieve the anaerobic situation it needs to set and harden. Although, in the past, whenever using the Blue 242 and Red 271, the fasteners it was applied to were always tightened and it would set as expected. Of course, the surfaces of the fasteners would always be meticulously cleaned before applying it.

 

   Yesterday, I put two, small drops of threadlocker on a plate, one of Loctite 242 and one of Permatex Blue, just to see if they would set up in the open air. This is to somewhat simulate application on a loose fastener. So far, both have not even begun to dry and have only spread. Have you tried this with yours? I would be interested to know if yours would begin to dry and appear to set in this way.

   This morning, after writing the post, I tried again with using this old stuff I have. Tomorrow morning, I will find out if it worked. 

 

Mark J.D.


Edited by Veridian, 21 June 2021 - 05:17 PM.


#36 biz

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Posted 21 June 2021 - 07:25 PM

   Graham (biz), thanks for this. I will go back and edit the post.

   I had read where some people have been keeping theirs in the fridge and then some others commented this should not be done. Your credible experience supports the former.

   After waiting the full 24 hours for the Blue 242 to set and harden and then finding it had not, I assumed it was because the vial I have here is quite old (20+ years?). This has not happened before, but then the nut in this circumstance was not fully tight either.

   I could not find any mention on the Loctite website where it stated the fastener had to be fully tightened to achieve the anaerobic situation it needs to set and harden. Although, in the past, whenever using the Blue 242 and Red 271, the fasteners it was applied to were always tightened and it would set as expected. Of course, the surfaces of the fasteners would always be meticulously cleaned before applying it.

 

   Yesterday, I put two, small drops of threadlocker on a plate, one of Loctite 242 and one of Permatex Blue, just to see if they would set up in the open air. This is to somewhat simulate application on a loose fastener. So far, both have not even begun to dry and have only spread. Have you tried this with yours? I would be interested to know if yours would begin to dry and appear to set in this way.

   This morning, after writing the post, I tried again with using this old stuff I have. Tomorrow morning, I will find out if it worked. 

 

Mark.

I haven’t tried this open air setup that you are trying so let’s wait and see, let me know what happens. Maybe the two surfaces need to contact before it works.

Most of my use is with stainless screws threaded into aluminium . I apply the loctite to both the internal thread and onto the external one. I screw the two together in and out a couple of times to get the spread, then leave it. It’s usually hand tight dry in about ten minutes. I just leave it over night before proceeding with my project. I’ve never had one let go after all these years . Some of my loctite is getting on in years also but it’s working so maybe the fridge is the thing.

cheers

Graham


Edited by biz, 21 June 2021 - 07:27 PM.

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#37 Veridian

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Posted 22 June 2021 - 12:02 AM

"Maybe the two surfaces need to contact before it works."

Graham, 

   Yes, this is what I am thinking and that the matching thread surfaces probably are supposed to have torque applied (tightened together). This is the only way I have ever used the threadlocker. 

    I am curious to learn if you have ever applied the threadlocker on two joined fasteners that have not been tightened? I haven't. If you have done this, did the threadlocker then set up and harden (without torque)? I am thinking that this is the situation with the round-nut on the axle, in that the nut can not be tightened enough to achieve the desired anaerobic condition it may need to fully set and cure (harden). 

   Are you using the Loctite brand of threadlocker, or Permatex brand? Also, about what temperature do you maintain inside your workshop fridge? I try to keep my kitchen fridge at about 37°F, otherwise the milk won't keep but a few days. Maybe this is too cold for the Loctite, I don't know.

   One more question, Graham: before application, do you use a primer, or just clean the threads real good?

 

-mjd



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Posted 22 June 2021 - 02:29 AM

   After writing post #33, I thought to try experimenting with the method described of adjusting and tightening the round-nut on the axle using this old Loctite 242 Blue threadlocker I have, just to see what happens. This is a long shot, as the Loctite is really old and the feeler gauge I ended up using as a stop to tighten the nut against is rather thick at .010".

   Once allowing the 24 hours for the Loctite to have a chance to dry, set up and harden, I will gently work the feeler gauge out from between the round-nut and thrust washer ("nylon"). It is a pretty good chance that .010" is going to be too much of a gap left and there will probably be too much side shake (slop) between the hub and the side-arm. Again, this is an experiment to learn if the Loctite will set up.

 

   In the photo, the nut has been snugged up against the .010" feeler gauge blade and this aligns the set screws in the nut just a bit to the right of the 3, pre-existing flats on the axle threads (described in post #33). The hope is that by having the nut snugged against the blade will create a thread surface to surface contact with the axle that is close enough (no rocking of the nut on the axle) to allow the anaerobic condition that may be needed to set up and harden the Loctite threadlocker.

   If the Loctite does set up as hoped, then I have a good indication this method will work and it can be re-done more accurately. I'll just have to wait this out until tomorrow, to see what happens.

Attached Thumbnails

  • StarPro AZ; ring-nut, adjust & tighten.jpg

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Posted 22 June 2021 - 02:36 AM

  Now, it's back to the azimuth control box and to have a look at what is under its hood. Photos and descriptions of removing the side-arm casting and attached azimuth hood are in posts 16 through 22.

 

  With the side-arm and hood removed from the azimuth (horizontal) control box, the clutch parts and azimuth worm ring-gear are now exposed.

 

 

Attached Thumbnails

  • StarPro AZ; azimuth control clutch assembly.jpg

Edited by Veridian, 22 June 2021 - 04:24 PM.

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Posted 22 June 2021 - 02:40 AM

  The side view of the stack of clutch parts, including the ring-gear.

 

From top to bottom:

  Axle, fixed. Unlike the altitude control axle, this one does not turn and is integral to the mount's aluminum, base casting.

 

Between the top, white plastic washer and the side-arm base that rests on it, there is at least one, very thin, transparent plastic washer. This 90mm mount has two of these.

 

  Washer, top (outer); plastic friction, white "nylon":  OD M40 x ID 20mm x Thk. 2mm 

 

  Pressure plate, stationary. Unlike the altitude clutch, this ring-nut is very tightly secured to the  axle (fixed) and does not have set-screws. It appears to be adhered to the axle with heavy duty, high strength threadlocker, such as Loctite Red 271.

 

  Washer, center; fibre friction

 

  Ring-gear, matched to the worm

 

   Washer, bottom (inner); plastic friction, white "nylon"

 

○  (white dot) Pressure plate, bottom floating. When the clutch is disengaged (loose) this plate floats on the axle and functions much like the outer, "pork pie hat" shaped pressure plate on the altitude control.

 

  The top, white, plastic washer and very thin, transparent plastic washer(s), are the only clutch parts inside the box that are easily removed.

Attached Thumbnails

  • rps20210621_051824.jpg

Edited by Veridian, 22 June 2021 - 04:03 AM.

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Posted 22 June 2021 - 03:54 PM

   The azimuth clutch's stationary pressure plate is seen here without the top (outer) friction washer. This pressure plate is a large round-nut (pin spanner nut) with two pinning holes and is screwed on to the fixed axle. Its function is much the same as the altitude control's inner pressure plate (round-nut with 3 set-screws), but without the set-screws that have been giving me trouble.  However, this round-nut is very tightly attached to the fixed axle.

   I tried to unscrew it from the axle, in order to have a look at the washers and ring-gear beneath. The two finishing nails can be seen as makeshift pins inserted into the plate's pinning holes. Although, the central axle prevents placing the lever close enough to the holes for getting proper control and leverage. The nut is fastened so tightly that the "pins" folded over as though made of soft aluminum. 

  This round-nut is fastened on really tight, and that's good, as this should prevent the unwanted dethreading that has been the problem with the altitude control's round-nut. Also, since there are no set-screws on this azimuth round-nut to loosen up, the attachment to the axle relies upon its threads being secured with a high strength, heavy duty threadlocker and not three, tiny set-screws.

   Should this nut ever need removing, I will need to apply heat for softening the threadlocker and to allow unscrewing. However, applying this heat (500°F) will likely damage the fibre friction washer directly beneath it.

Attached Thumbnails

  • StarPro AZ; azimuth, clutch press. plate - fixed.jpg

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#42 biz

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Posted 22 June 2021 - 05:26 PM

Graham, 

   Yes, this is what I am thinking and that the matching thread surfaces probably are supposed to have torque applied (tightened together). This is the only way I have ever used the threadlocker. 

    I am curious to learn if you have ever applied the threadlocker on two joined fasteners that have not been tightened? I haven't. If you have done this, did the threadlocker then set up and harden (without torque)? I am thinking that this is the situation with the round-nut on the axle, in that the nut can not be tightened enough to achieve the desired anaerobic condition it may need to fully set and cure (harden). 

   Are you using the Loctite brand of threadlocker, or Permatex brand? Also, about what temperature do you maintain inside your workshop fridge? I try to keep my kitchen fridge at about 37°F, otherwise the milk won't keep but a few days. Maybe this is too cold for the Loctite, I don't know.

   One more question, Graham: before application, do you use a primer, or just clean the threads real good?

 

-mjd

Mark,

I’m using the original Loctite thread locker.  It just works for me so I stick to it. I just store it the fridge under normal food temp.

I do not use the primer but I clean the threads with degreaser and blow them dry with my compressor. As I mentioned before ten minutes and they are hand tight dry .

By the way I’ve been reading this thread of yours and found it interesting , so I sort of thought you might be interested about my uses with thread-locker.

cheers

Graham


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#43 Veridian

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Posted 22 June 2021 - 10:40 PM

Graham,

   Thanks for getting back with answers to my "twenty questions". Over the years, I'vs been doing the application the same as you describe. But, this is my first situation applying the threadlocker to a loose fastener.

   Just before hitting the rack this morning, I did an application of both Loctite and Permatex (blue) to a pair of allen screws and matching nuts. After cleaning them good, I put a drop on each and left both nuts loose on the screws. I checked them this afternoon and both had set. I didn't force them, but the nuts were "locked" in place. So, you're right about the age of this stuff probably not making a whole lot of difference. Maybe I didn't get the threads clean enough on the round-nut and axle, on the first attempt. I don't know what went wrong.

   In a few hours, I will remove the feeler gauge blade (post #38) and see if this 2nd attempt works out. The Loctite has had well over 24 hours to cure and set. We will see what happens.

 

   It is good that you came across this thread and found it interesting enough to comment about your Loctite use experience. Your comments have been most helpful, Graham.

 

Best regards and thank you, again,

Mark


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#44 biz

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Posted 23 June 2021 - 12:45 AM

Graham,

   Thanks for getting back with answers to my "twenty questions". Over the years, I'vs been doing the application the same as you describe. But, this is my first situation applying the threadlocker to a loose fastener.

   Just before hitting the rack this morning, I did an application of both Loctite and Permatex (blue) to a pair of allen screws and matching nuts. After cleaning them good, I put a drop on each and left both nuts loose on the screws. I checked them this afternoon and both had set. I didn't force them, but the nuts were "locked" in place. So, you're right about the age of this stuff probably not making a whole lot of difference. Maybe I didn't get the threads clean enough on the round-nut and axle, on the first attempt. I don't know what went wrong.

   In a few hours, I will remove the feeler gauge blade (post #38) and see if this 2nd attempt works out. The Loctite has had well over 24 hours to cure and set. We will see what happens.

 

   It is good that you came across this thread and found it interesting enough to comment about your Loctite use experience. Your comments have been most helpful, Graham.

 

Best regards and thank you, again,

Mark

Mark, I’m always interested in any one who wishes to mod or repair their telescope items..

Im in my late 70’s and grew up having to repair things as it was not the throw away age as it is now.

We gained a lot of knowledge on how things were put together so I’m not frightened to pull a mount apart (or whatever) to find out how it works and to see if I can make it better. It’s a lot lot of fun as I’m sure you are finding as well. Sometimes we finish up on the right side of the ledger , sometimes not , if so the latter then it’s easy to go back to square one.

Im sure you will get your mount purring like a cat.

cheers

Graham


Edited by biz, 23 June 2021 - 12:46 AM.

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#45 Veridian

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Posted 23 June 2021 - 06:04 AM

Mark, I’m always interested in any one who wishes to mod or repair their telescope items..

Im in my late 70’s and grew up having to repair things as it was not the throw away age as it is now.

We gained a lot of knowledge on how things were put together so I’m not frightened to pull a mount apart (or whatever) to find out how it works and to see if I can make it better. It’s a lot lot of fun as I’m sure you are finding as well. Sometimes we finish up on the right side of the ledger , sometimes not , if so the latter then it’s easy to go back to square one.

Im sure you will get your mount purring like a cat.

cheers

Graham

Graham (biz) wrote:

"Im in my late 70’s and grew up having to repair things as it was not the throw away age as it is now.

We gained a lot of knowledge on how things were put together so I’m not frightened to pull a mount apart (or whatever) to find out how it works and to see if I can make it better. It’s a lot lot of fun as I’m sure you are finding as well. Sometimes we finish up on the right side of the ledger , sometimes not , if so the latter then it’s easy to go back to square one."

 

   Very, very well said, Graham. I do not believe anyone could have found words that would have said it better. waytogo.gif

 

Mark


Edited by Veridian, 23 June 2021 - 06:29 AM.


#46 Veridian

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Posted 23 June 2021 - 06:22 AM

 Castor ?

 

   You've been at this for many years and I have been wondering if you have had any interesting threadlocker experiences that you may want to tell us about.

 

Mark J.D.


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Posted 23 June 2021 - 12:32 PM

 Castor ?

 

   You've been at this for many years and I have been wondering if you have had any interesting threadlocker experiences that you may want to tell us about.

 

Mark J.D.

 

Hi Mark,

 

No, I’m afraid I don’t!  When I was a kid I didn’t have the money to buy telescopes or accessories so I used parts from busted binoculars to build mini-scopes and lenses from old cameras to make my eyepieces so I could get more magnification from them and look at deep-sky objects more closely –I even added my own crosshairs using thin copper wire from radio tuners to make my first 40mm finder scope to add to my first Tasco 50mm department store telescope.  But I am a mechanically challenged person (not good at disassembling things and then putting them back together to the original specs) so once I started earning enough to afford real telescopes I started using my inclination to “improve things” by integrating parts from different manufacturers (mounts, tripods, telescopes, diagonals, finders, eyepieces, adapters, etc.) to get as close as possible to my concept of the ideal telescope for a particular purpose, in other words a modular observing system instead of a package sold by a commercial vendor.  That philosophy helped me through the years to slowly build my current stable of telescopes and observing equipment because with my limited disposable income I could only buy one piece of equipment at a time –it took me 15 years to acquire my 5-inch refractor!

 

I have been following your excellent documented thread with interest, not only because I’m curious to see what these mounts look like from the inside, but mostly because I feel admiration for people who have the know-how and mechanical skills to perform complex tasks and then go to great lengths to share their knowledge with others, without expecting any remuneration or acknowledgment for it!  I know that you will feel rewarded when fellow amateurs having awful backslash problems with their Meade StarPro Az Mount finds this thread with a complete step-by-step guide to help them fix it themselves!  Maybe they won’t be able to personally thank you if they are not Cloudy Nights members, but please let me THANK YOU! in advance on their behalf.


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#48 Veridian

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Posted 23 June 2021 - 07:21 PM

Castor,

 

   That is a good recount of your early experiences with telescopes, but I balk at your claim of being "mechanically challenged". Although, I too am having trouble remembering the correct sequence of putting something back together. With the advancing years, the memory does not get any better with many of us, so to help with the re-assembly, this all began as a photo documentation of my disassembly of the mount.

   Again, Castor, I thank you for the recognition and kind compliments on the posts, as well as for your words of encouragement. 

 

All the best,

Mark


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Posted 23 June 2021 - 08:20 PM

  I may have come across the problem, as to why the threadlocker compound is not setting up on the round-nut to axle threads. Early this morning while in bed, I was woken up and began thinking over this problem.   

   Last night, when again cleaning the threads on the axle and round-nut, after rinsing off the suds with warm water, the flat surfaces of the nut had an out of the ordinary slippery feel to them. It was as though there were still some oil or grease left behind that may be anhygroscopic. Giving it a good wipe down with isopropyl alcohol, it was then cleaned again with dish soap and warm water. Same thing. WTH? When a part is cleaned in this way, it normally has a squeaky, grabby feel between the fingers. The flats on this nut still had that slippery feel, as though it were made of nylon or teflon.

   The parts were then thoroughly dried and warmed for a few hours to ensure there was no remaining moisture on them. Another application of threadlocker was applied and the parts assembled as before and I hit the rack for some sleep.

 

   When lying in the rack and thinking about this, I realized these parts are anodized aluminum. I began wondering if the anodizing may be the reason for the slippery surface. This afternoon, going to the Loctite website (Henkel), I found that anodized thread surfaces need to be primed with Loctite Primer before curing and set up can happen. They list a number of different metals and materials that require priming. The first time around, reading this section, I missed the anodized surfaces mention.

    After reading this, I then checked the round-nut on the axle and the threadlocker (using Permatex Blue, this time) applied the previous evening. It had not even begun to set up and cure. 

   The experiment done two days before, with the pair of allen scews and nuts, showed the Loctite and Permatex threadlocker was still good enough to set up, cure and harden the join between the loose nuts on the allen screws.  The Permatex blue gave a noticeably better lock than the Loctite 242 blue, but there could be many reasons for this. While it certainly was not a scientific experiment, it did show that the age of each old vial I have has little to do with the set up, curing and hardening - as noted by Graham (biz) earlier.


Edited by Veridian, 24 June 2021 - 01:45 AM.

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Posted 23 June 2021 - 10:10 PM

  I have been wondering how you guys actually found this thread. On my CN Forums page, the "Equipment Discussions" section has been compressed to where only its greyed out title appears. It is very difficult to see and easy to miss. Maybe this is only from the connection at my end.




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