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

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#1 Veridian

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Posted 12 June 2021 - 09:39 PM

  This is for anyone that may be curious about what the StarPro mounts' slow-motion controls and clutches look like "under the hood". You may be considering buying one of these models, or already own one.

   I have found these to be excellent starter telescopes and can be a nice gift. The mount and tripod unit is well made, stable, sturdy and highly portable. I have both the 70mm and 90mm. The 70mm was purchased as an economical "grab & go" telescope. I liked it so much that I wanted to try a 90mm. Once I learned how to use it right, image settling time for the 70mm is 1 second at most and usually less. Before adjusting the 90mm, it was noticeably more, but now it is about 1.5 seconds and 2 at most. On both scopes, It took a little getting used to the spring stalks on the control knobs and to gently release them without any bounce. This is pretty much the primary source for image shake. Although, the spring stalk design is definitely a needed safety feature to help prevent snapping off the 1/4 inch brass control shafts, when moving the telescope about.

    Out of the box, slow-motion controls on the 70 were near perfect in operation. The more recently purchased 90mm needed adjustment. Both altitude and azimuth controls were much too stiff -- even with the clutch fully off. I found this to be the main cause for image shake, when tracking with the slow-motion controls. 

  There was, however, one thing about the 70mm altitude control in free tracking (clutch disengaged) that could be better. It was too loose. When taking tension off the clutch, the scope would droop, if not near perfectly balanced. This became annoying when changing eyepieces of different weights. In addition, the azimuth (horizontal) clutch knob needed to be quite tight, to allow the slow motion to engage and this also could be better.   

  So, I decided that a look under the hood of both telescopes was in order, to see what was going on. Photos were taken as the adjustment process went along. It was a surprisingly simple process and much easier than other alt-az mounts, including a few earlier Meade models and a Vixen Mini-Porta Mount.

 

   The first photo that follows this introduction just shows the two scopes, side by side, in their maximum elevation-declination positions. The mounts are the same for entire line.

 

Mark J.D.


Edited by Veridian, 13 June 2021 - 03:27 PM.

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#2 Veridian

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Posted 12 June 2021 - 09:43 PM

The Meade StarPro 70mm and 90mm in their maximum elevation and declination positions.

 

 

Attached Thumbnails

  • StarPro AZ 70 & 90; full elevation & declination.jpg

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#3 Veridian

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Posted 12 June 2021 - 09:57 PM

The tools I used for making the clutch and control adjustments.

 

Both clutch knobs are shown. The clutch knob for azimuth (horizontal) control has a longer and larger diameter thread. Also, there is an "e-clip" (circlip) affixed to its end (not shown). When loosening, once there is resistance, if one continues trying to turn off the knob, the e-clip will pop off onto the floor. If your luck is anything like mine, this clip will then become nearly impossible to find, as it travels to the most inaccessible and darkest part of the room. This will also distort the clip. It is not really needed though, so if it gets away and is trying to hide somewhere, one need not indulge its game of hide & seek.

 

The vernier caliper and small mill file are not necessary, but I did use these for modifying the small allen wrench seen here, as described in a post below.

 

 

Attached Thumbnails

  • StarPro AZ; tools used for alt-az cntrl adjustment.jpg

Edited by Veridian, 13 June 2021 - 07:38 AM.

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#4 Veridian

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Posted 12 June 2021 - 10:29 PM

  Beginning with the 70mm altitude control on the side-arm, once the clutch knob is spun off (no circlip on this one) the three allen, socket-head screws are accessible that hold down the assembly cap -- the "hood". 

   Here is the line-up of the clutch parts, as they come off.

 

L to R:

a.   Clutch control knob.

b.   The "hood", upside down, with its three, 2.5mm socket-head allens.

c.   Clutch "pressure plate" (out-side down). This a loose, slip fit over the central axis, drive-shaft and easily falls off.

d.   Two, white nylon, friction discs. These can be a tight fit against the drive-shaft. Care must be taken when removing, to prevent distortion.

e.   Alloy worm ring gear* (aka ring gear), face down. This should also be a snug, slip fit on the axis drive-shaft. Placing a mark on the facing side will help avoid flipping when putting it back in place. I put 3 dots on it with the blue Sanford marker, just in case one gets rubbed off. Turning the slow-motion stalk, to activate the brass worm (the rotini gear), will enable the ring gear to slip right off. [This was pinched in place on the 90mm and a puller had to be used. More on this later.]

f.   Dark grey, inner friction disc made of fibre. It has two holes punched in and it rests against the large "round nut" that adjusts the drive shaft play. More on this later, as well.

 

 

*The technical term is worm gear. But, to avoid confusion with the actual brass worm, from here on it will be referred to as the ring gear, or worm ring gear.

 

Attached Thumbnails

  • StarPro Alt. control; clutch assembly.jpg

Edited by Veridian, 13 June 2021 - 05:02 PM.

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#5 Veridian

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Posted 12 June 2021 - 10:39 PM

  This is how the altitude assembly looks, once the "hood" is removed. Maybe this photo should have preceeded the parts layout. Oh well, please excuse the sequencing.

 

As the parts are removed:

1. Clutch pressure plate -- metal with black, oxide finish. (c. above)

2. Two, friction washers -- white nylon (d. above). Concealed beneath pressure plate

3. Alloy, ring gear (e. above)

4. Friction washer, inner -- dark grey fiber, with two holes (f. above). Concealed beneath ring gear.

 

Attached Thumbnails

  • StarPro alt. control; under the hood.jpg

Edited by Veridian, 13 June 2021 - 02:25 AM.

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#6 Veridian

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Posted 12 June 2021 - 10:59 PM

Altitude control assembly with primary clutch parts removed.

 

Up to this point, I have probably not risked voiding my warranty. From here on, however, if a person has that concern, it may be best to just look at the photos, but don't touch. These telescopes were given  several weeks to allow enough use and time for me to decide if they are keepers. I am now committed.

 

The photos that will follow are going to show how adjustments were done and with some explanations on how I did them. It should be mentioned that whenever working with tools and small parts, I always wear adequate eye protection. I learned that lesson the hard way, many years ago.

 

As a disclaimer, I have no affiliation with Meade Instruments Corporation. I am not advising these adjustments, unless one feels comfortable and confident with the process. Then again, I found this design quite straightforward to work with. It is well designed and uses quality materials.

 

Attached Thumbnails

  • StarPro Alt.cntrl; round nut set screw locations.jpg

Edited by Veridian, 13 June 2021 - 08:36 PM.

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#7 Veridian

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Posted 13 June 2021 - 12:34 AM

  As was mentioned earlier, the problem I was having with my Star Pro 70 was that the altitude, free scanning position was much too loose. When going to find another eyepiece, by the time getting back the object was often too far out of the field of view. To speed things up relocating it, the altitude clutch knob would be loosened for quickly recentering. If the eyepiece had too much difference in weight, with the clutch loose, the scope would droop and I would end up way off target. So, I wanted to tighten this up some.

 

   In this photo, there is the large, "round-nut" that is threaded onto the drive-shaft. This is what adjusts the tension of the scope free movement on the axis. It also functions as the inner pressure plate for the clutch.

   When the clutch knob is tightened, the ring gear that free spins on the driveshaft is then pinched between the dark grey, fibre washer that rests against this large, "round-nut" and the two, white nylon, outer friction washers that rest against the floating, outer, pressure plate (#1 in post 5). Without these three, clutch friction washers (1 fibre and 2 nylon), there would be metal to metal contact against the ring gear when it is pinched between. That would not be good. These three friction washers allow for a gradual and firm, power transfer engagement.

   

   To adjust tension (firmness) for the free movement of the driveshaft within the mount's stationary arm, I needed to slightly tighten this large, black, "round-nut". There are 2 opposing holes in the face of this nut. One hole is clearly seen in the photo and because when working a camera I can't think of everything, , the other is on the opposite side and blocked from view by the driveshaft.

  These holes are designed for a match up with a pin spanner wrench. Although, in this case, the nut is not wrenched tight on the threaded driveshaft, so a spanner is not needed. The nut is kept in position on the driveshaft by three, tiny, allen socket, set screws (aka grub screws). These 3 set screws are on the outside edge of the round-nut at 120° intervals and lock the round-nut against the driveshaft. Three red dots can be seen that mark their location. With the set screws loosened, the nut turns fairly freely. The external threads of the driveshaft can be seen just barely peeking out from the inner edge of the round-nut. The internal threads of the driveshaft are, of course, for the clutch knob.

   

 

Attached Thumbnails

  • StarPro Alt.cntrl; round nut set screw locations.jpg

Edited by Veridian, 13 June 2021 - 12:50 AM.

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#8 Veridian

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Posted 13 June 2021 - 01:38 AM

   The hardest part of this project was finding the right size allen wrench to fit the 3 socket screws that secure the large round-nut. A 1.5mm allen wrench was too loose and 5/64th in. too big.  I think the socket size is 1/16th inch, and wouldn't ya know it, I could not find my 1/16th allen wrench.

   I had an extra 2mm allen, so it was tediously filed down to where it would fit. The roughest part, during the filing, was keeping the flats and angles correct. When at last it fit, the measurement of the allen wrench tip was 0.062" in. and that equates to 1/16th inch. The time spent looking for that 1/16th" wrench and then accurately filing off less than a half mm of the 2mm wrench took the better part of two hours. 

   Thankfully, the 3 set screws (grub screws) were not overtightened and no Loctite was used. They easily loosened. When doing the adjustment, to get the best leverage and control on the roundnut, I filed the tips off of two finish nails to insert into the two holes of the nut. With scope on the mount and the roundnut set screws loosened, I turned the roundnut snug to pre-load it and then slighty turned it out and found what felt to me was the right tension and snugged the set screws. This took a couple of attempts, to get it just right, pre-loading each time. Once satisfied, the 3 set screws were then tightened just enough to keep them from working loose. 

    Now, with the clutch loosened, a heavier than stock diagonal and a moderate weight eyepiece, the scope moves freely in the scan mode and without drooping. Even when the scope is a little off balance, it now works like I want it in the free mode. With the clutch snugged, the slow-motion controls engage properly, turn smoothly and with minimum backlash.

 

Next up, clutch reassembly, , adjusting tension on the slow-motion control shaft and worm gear to ring gear backlash.

Attached Thumbnails

  • StarPro Alt. cntrl; round nut tension adjustment.jpg

Edited by Veridian, 13 June 2021 - 07:53 AM.

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#9 Veridian

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Posted 13 June 2021 - 09:06 PM

   Reassembly of the clutch parts is just a simple, reverse process and begins with the fiber, friction washer (see photo). The three set screws on the large round-nut were double checked for correct * tightness. The contact surfaces of both pressure plates (the dual purpose, large, inner round-nut and the outer, hat shaped sleeve) and all three friction washers were inspected to ensure they were clean and dry. Running my fingers over them ensured there was no grit stuck to them.

   The alloy ring gear (worm gear) slides back on the drive shaft with same side facing in as it came off. Turning the brass worm (rotini gear), while sliding it into place, aligns the gear teeth, keeps it from pinching and raising a burr on the engaging teeth edges. 

   The two, white nylon, friction washers are next and followed by the outer, black anodized, aluminum alloy, pressure plate. Hold off replacing the "hood" (cover). 

 

*As the telescope does not experience the vibrations and shocks of a motorcyle or automobile, there are few fasteners that require high torque tightness. Overtightening causes more problems than undertightening

 

   Checking the worm gear assembly's backlash is next.

 

Attached Thumbnails

  • StarPro Alt. cntrl; clutch inner friction wshr..jpg

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#10 Veridian

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Posted 13 June 2021 - 09:35 PM

   When the clutch is tightened and the altitude control's slow-motion mode is engaged, it should be smooth, without stiction and have a minimum of backlash. This is how the controls work on my 70mm and nothing needed to be done. The 90mm was a different story and required some attention. 

   I keep in mind that a little backlash is needed to prevent premature wear on the worm and gear teeth. I figure it by watching how much of an arc (or how much of a full turn) the slow-motion knob and set screw on the stalk make while in the backlash pause, remembering that 1/4 turn is 90 degrees, 1/8th turn is 45°, 1/16th turn ~23° and so on. When changing direction and as the action re-engages, 5 to 10 degrees is plenty and 15° is approaching excessive. Some years back, another name brand of alt-az mount came to me brand new, out of the box, with 90 degrees of backlash!

 

   Backlash and the tightness of the brass control rod are adjusted two ways. One is the mesh of the teeth on the worm ("rotini gear") to the large, ring gear. Before making an adjustment here, I was careful to place scribe marks on either side of the worm block. 

   The other adjustment is the small, aluminum, slotted round-nut on the long, 1/4 in.* dia, brass worm shaft -- the part the control stalk is affixed to. [a red dot was placed on this nut in the photos] This is a compression nut and determines the resistance of how the brass rod turns. If it turns too tightly or is sticky, this can be loosened slightly, but doing this will also add some backlash. This is why I did this adjustment first, before moving on to adjusting the worm and gear backlash.

   At this point, I can spin the clutch knob back on for checking my work. In the one photo, showing the reassembled clutch parts, the outer pressure plate (the hat shaped part) is seen about to tip off of the driveshaft. I didn't notice this until after the photo was taken, resized and posted. Ooops.

 

* More accurately, the "1/4 in.", brass shaft actually measures 0.235 in. (6.0 mm)

Attached Thumbnails

  • StarPro AZ; worm & gear assembly.jpg
  • StarPro AZ; comp. nut w-red dot.jpg

Edited by Veridian, 14 June 2021 - 07:54 PM.

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#11 Veridian

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Posted 13 June 2021 - 09:54 PM

   Before making any adjustments for the backlash, reference marks were placed at each end of the aluminum support block for the worm shaft (see bottom photo in the above post). This block is secured in place by the two, stainless steel, 2.5mm socket, allen screws. A sharp pointed scribe was used and marks made, before loosening the 2 allens. Even if the original, factory adjustment is off, I want to know the starting point when doing the adjustment.

 

  First off, the adjustment for the brass, worm shaft was taken care of, before checking the worm to ring-gear mesh. This is done with the small, slotted, compression nut (see photos above).

  To keep from marring it, I did not want to use common pliers to turn this slotted, ring nut, so a special tool needed to be made. I don't know what to accurately call it, so I'll just say it's a dual spline sleeve wrench. An old, bronze valve guide from a motorcycle was used and has an internal bore close to the 1/4 in. diameter of the brass, worm, drive shaft. It took a while to make, carefully using a couple of sharp and high quality mill files. This bronze is very hard and can easily damage the teeth on the file. The work was slow going and it isn't my best, but it does the job.

   I have since found that while this tool is convenient, it is not really necessary, as the nut is not all that tight on the altitude control. It is, however, different on the azimuth side.

   If a person is careful, a pliers could be used. Along with a piece of leather, rubber or card in the jaws, this nut could be loosened and retightened and not leave marks. Better yet would be making a spanner wrench from a 1/16th in. thick metal plate (brass or steel), 1/2 in. wide and 6 in. long. At one end, with a good, machinist's round file, this metal strip can then be shaped into a fork to fit around the 1/4 in. brass drive shaft. The fork tips are then bent over 90° -- using some heat to relieve some temper and help prevent cracking. These two, bent over tips can then be easily filed down to shape with a small, mill file to snugly fit into the round-nut's 2 slots. 

 

   As mentioned, the azimuth control is different and will be described further on.

   

Attached Thumbnails

  • Compression nut spanner; 2.jpg
  • Compression nut spanner; 1.jpg

Edited by Veridian, 14 June 2021 - 07:33 AM.

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#12 Veridian

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Posted 13 June 2021 - 11:06 PM

Here is a drawing I made for a simple slot spanner wrench and that is described in the post above.

Attached Thumbnails

  • StarPro; slot spanner for compress. ring nuts.jpg

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#13 Castor

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Posted 14 June 2021 - 05:28 PM

Hi Veridian,

 

Thank you for your well documented and well-illustrated look inside and step by step guide for fine tuning the mount of these attractive-looking, entry level alt-az refractors from Meade, I’m sure it will be appreciated by owners and potential buyers!

 

My first “serious” telescope was a Meade 90mm achromatic refractor and it was key in developing my appreciation for the no-fuss, no wait (for acclimatization), high contrast, crystal clear views provided by this wonderful type of instrument!

 

Keep up the good work! waytogo.gif 


Edited by Castor, 14 June 2021 - 05:30 PM.

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#14 Veridian

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Posted 14 June 2021 - 08:03 PM

Hello Castor,

 

Thank you for all of the Likes and your kind words of encouragement. Once the series is completed, I will write a more appropriate reply to your post.

That is quite the impressive herd of telescopes you have there in your stable.

 

Again, thank you,

Mark J.D.


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#15 Veridian

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Posted 14 June 2021 - 10:09 PM

   Adjusting the altitude worm and ring-gear backlash on this mount is a simple and straightforward procedure. Its design is well thought out and the materials used are of good quality. The machine work is well done, accurate, with nice finishing and all quite surprising for a mount in this price range.

 

   Some backlash between the teeth of the worm and ring-gear is required to prevent premature wear, but too much isn't good and makes for clumsy tracking. It is the amount of space between the teeth as they mesh that determines this. If the teeth are pressed in to each other too tightly, there is no room for lubrication between the sliding surfaces of the gear teeth and this increases the friction and wear. 

 

    Once again, before I loosened the two allen socket screws on the worm block (2.5mm socket) to do the adjustment, a reference mark was scribed on either side of the block where it mates with the side-arm casting. I always like to know where the starting point is.

    Loosening the two allens with the 2.5mm allen wrench, I have one hand gripping the worm block and the ring-gear. With the allen screws just barely loose, the two gears are gently squeezed together and the allen screws then snugged up. I have found that squeezing the two gears together between my fingers and thumb do as good as any other way of centering and aligning the mesh. [when taking the photo, I did not want to cover up the ring-gear with my finger]

 

   Spinning the clutch knob back on and tightening it up, the telescope tube is reattached onto the mount and backlash is checked with the slow-motion knob. For the free backlash between directional engagement, I am looking for an optimum of 5 to 10 degrees arc*. A 32nd of a full turn of the slo-mo knob is 11.25 degrees arc. Watching the movement of the set-screw on the slo-mo stalk is a fairly accurate way to determine this. The optimum can be be a bit tedious to achieve and so I can easily deal with 15 to 20 degrees. For me, a maximum backlash of 1/16th turn (22.5° arc) is acceptable.

    Before closing the "hood" (replacing the cover), the work is checked again. I want a smoothly turning slow-motion shaft and acceptable backlash, when changing directions. I loosen and retighten the clutch a few times, to allow all the reassembled parts to settle in together and to be more certain of my adjustments.

 

   There is usually an excess of squeezed out grease on the sides of the ring-gear and this will be re-distributed with my finger around the teeth of the gear. Without knowing the exact alloy content of the ring-gear, I don't like to change the grease and am content to stay with what the factory applied. Using the wrong grease can induce a galvanic corrosion situation between the dissimilar metals of the worm and ring-gear. I don't need microscopic pitting developing on the surfaces of the gear teeth.

   The hood is then replaced and as with any cover secured by multiple fasteners, each of the three allen screws (2.5mm socket) then aligned and threaded in loosely before staggering their snugging down. Once again, these need only be barely tightened, since they are not going to be shaken or vibrated loose.

 

*These figures contradict what I wrote in post #10, which should have been written, "5  to 10 degrees is optimum, 15 to 20 degrees acceptable and 30 degrees approaching excessive".

When going back to edit the post, the edit option had already been turned off. Please excuse the mistake.

Attached Thumbnails

  • StarPro AZ; worm & ring-gear adjustment; 1.jpg
  • StarPro AZ; worm & ring-gear adjustment; 2.jpg

Edited by Veridian, 14 June 2021 - 10:29 PM.

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#16 Veridian

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Posted 15 June 2021 - 06:25 AM

  The azimuth control box is next and there are differences from the altitude control.

  First, before spinning off the clutch control knob, a circlip (E clip) must be removed from the groove on the end of its threaded shaft. This is underneath the mount. (red dot in photo).

  The usual way of attaching a circlip is to install it with the sharp edge facing the thrust side. This clip is attached with the rounded side facing out - the thrust side. I suspect this is for when a person forgets, or is not aware of its being there, and turns the clutch knob fully out for removal. This reversed attachment allows for the clip to pop off the shaft, instead of damaging the groove. Installed in this manner (rounded edge out), when fully unthreading and removing the knob, forcing the clip off will distort the clip, but is less likely to damage the end of the shaft.

 

  Should the clip be badly damaged, or lost, a replacement can be had at a hardware or auto parts store. I suspect that its purpose is primarly keep the knob in place when loosened, as it is only secured with a minimum of threading in the flange nut beneath the box.

  This flange nut is fastened with 3 phillips screws to the 3 posts of the clutch's lower pressure plate. These 3 posts extend through 3 holes (2nd photo, w/flange nut removed) in the mount's lower casting.  With the clutch knob loose, this lower pressure plate floats on the central axle. It performs the same function as the floating, outer pressure plate (shaped like a pork pie hat) on the altitude control. Quite a clever design, this is.

 

Attached Thumbnails

  • StarPro AZ; azimuth clutch knob circlip.jpg
  • StarPro AZ; azimuth clutch. lwr press plate posts.jpg

Edited by Veridian, 16 June 2021 - 05:44 AM.

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#17 Veridian

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Posted 15 June 2021 - 07:14 AM

Close ups of the E-clip (circlip) clearly showing the difference between the rounded and sharp edges.

 

Removing the clip is easily done with a small screwdriver and  needle nose pliers.

I got a bit rough, when taking this one off and distorted it slightly, but it's not a difficult fix. If looking closely, you may notice this. All around, it has not been one of my better days. 

 

. . . more to follow.

Attached Thumbnails

  • StarPro AZ; circlip, azimuth clutch knob.jpg
  • StarPro AZ; circlip, azimuth clutch knob shaft.jpg

Edited by Veridian, 15 June 2021 - 07:25 AM.

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#18 Veridian

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Posted 15 June 2021 - 08:06 AM

   With the clutch knob spun off, I am now able to remove the side-arm casting and access the hood below it. These are held in place with a dual function round-nut that is threaded onto the central axle. This is a precision machined round-nut and has two holes, instead of slots. The two holes in the nut are a little hard to see in the photo. 

   The primary function of this round-nut is to adjust the correct pressure upon the thrust bearing directly beneath. Along with the thrust bearing's bottom race, it also keeps the side-arm in place, controls its free spin and prevents side shake in the arm when properly adjusted. In short, it holds the entire azimuth box assembly together.

   Removal was a little more involved than what I had expected and was the most difficult part of the entire project. This will all be explained in the following posts. 

 

 

Attached Thumbnails

  • rps20210615_053635.jpg

Edited by Veridian, 16 June 2021 - 12:21 AM.

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#19 Veridian

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Posted 16 June 2021 - 01:23 AM

   Before getting too far into this, here is a photo of the tools used on the azimuth contol box. These are much the same as used for the altitude control. Although, two tools were forgotten to be included in this photo, but were in the earlier photo: the scribe and the small, mill file.

 

Allen wrenches: 2.5mm and 1.5mm. The 1.5mm allen in the Ecklind set measured slightly too small for a proper fit in the worm block's set screw (grub screw). The one pictured fits the set screw socket snug and correct.

 

Sanford blue marker, for placing reference marks on the end of the central axle. 

 

Screwdrivers: a common, long shank, standard flat-tip and the Phillips included with the telescope.* 

 

Spline nut wrench, fashioned from a 3/8" diameter, K&S aluminum tube with 0.049 in. wall thickness (6061-T6 alum.). Online Metals sells 3/8 alum. tubing (6061-T6) with thicker walls and hence a very close fit on the brass, worm shaft. A closer fit helps prevent the tool from rocking out of the slots on the nut and the thicker wall allows for  more substantial splines to fit the slots.

 

A drill bit and finishing nail (next to the round-nut) to serve as pins for a makeshift spanner wrench, in lieu of a proper pin spanner.  Used to loosen, adjust and retighten the central, precision machined, round-nut.

 

Loctite #242 Blue thread locking compound for the round-nut.

 

An ordinary 5 cent piece for the coin slots in the set screws on the control stalks.

 

* The sharp tip of this Phillips screwdriver is filed down by about 1/2mm, as it otherwise bottoms out in a Phillips screwhead socket. When bottoming out, the 4, tapered splines of the driver tip do not fully engage the facets of the screwhead's 4 splines. This causes "cam out" which ruins the function and appearance of a Phillips head screw. Slightly reducing this point helps prevent "cam out".

 

 

. . . and again, as with any mechanical operation, repair or adjustment, suitable eye protection is always worn.

Attached Thumbnails

  • StarPro AZ; azimuth control adjustment tools.jpg

Edited by Veridian, 16 June 2021 - 05:16 AM.

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#20 Veridian

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Posted 16 June 2021 - 02:37 AM

   Loosening the central round-nut on the azimuth's fixed axle is a bit of work. As already mentioned, this round-nut has a dual purpose. It not only holds the entire azimuth assembly together, but it is important for setting the proper load on the thrust bearing (needle bearing) immediately beneath. To prevent its loosening, a threadlocking compound was applied to its threads at the factory. 

   Before proceeding with loosening this nut, I placed a couple of marks on the axle with the Sanford blue marker. The blue ink works better than black. These two marks were placed adjacent to the two pin holes in the round-nut. These marks will be the reference point when re-installing the nut, during reassembly. It will be easier to preload the bearing and to have a good idea how far to back the nut off for setting the right thrust on the bearing beneath it.

 

   In other mechanical situations, where the use of threadlocking compound makes it difficult to remove a fastener, I would usually apply controlled heat from a torch. The heat softens the compound and makes it really easy to break the fastener free. For a couple of reasons here, I did not want to use heat. Were I to have a good oxy-acetylene set-up with a fine tip for soldering and brazing, or a precision, jeweler's torch with its micro flame, then I would consider using heat. I don't, so I had to do this the other way and which was a little more work.

 

    This round-nut has two holes that are designed to be matched with the correctly fitting pins of a pin spanner wrench. Not having the right size pin spanner, the improvised method was used. The two pins in this case are a drill bit (5/64ths"; 0.078"; #47) and a finishing nail with its tip filed off. The leverage is provided by a common, flat-tip screwdriver with a long shank. (see photo)

    Without having the advantage of using heat, in order to loosen the round-nut without damage to the threads and nut, the hardened threadlocker had to first be broken free from the threads. Quite often this can be successfully accomplished in other situations by first tightening a fastener a slight bit. Seems counter-intuitive, but it often works and is a trick I learned from an old, master mechanic many years ago as a young apprentice. This trick often works with rusted on fasteners, also. In the case of this round-nut, since one of its main functions is as an adjusting nut for the thrust bearing beneath, it was not going to be tightened against the washer below, as would an ordinary hex nut. 

   For the optimum leverage and control, the shank and blade of the screwdriver must be brought as close to the work (the nut) as possible. In this case, the blade can nearly rest upon the nut. One half inch higher and it likely would not work.

   With the screwdiver's blade set between the two improvised pins that were being gripped between the thumb and fingers, a firm but controlled twist was made slightly clockwise (~1/32nd turn), as though tightening the nut. It could be felt to barely move and this was an indication the hardened, threadlocker compound was breaking loose. Then, the screwdriver's blade was repositioned between the "pins" and a firm, controlled, counter-clockwise turn made. The round-nut slowly turned free.

   To prevent loading and clogging the threads with the hard particles of the threadlocker compound, the nut was turned back and forth, i.e., 1/4 loose and then back the other way an 1/8th turn. This "to and fro" action allows the particles to dump out of the thread cuts and helps prevent them from damming up and jamming the threads. After about a full, counter-clockwise turn (maybe a turn and a half) in this manner, the nut freed up and easily turned off. The most difficult part of the operation was then accomplished and without mishap.

 

In the photo, the screwdriver is shown in the clock-wise, adjusting and tightening position.

Attached Thumbnails

  • StarPro AZ; azimuth cntrl. round-nut removal.jpg

Edited by Veridian, 16 June 2021 - 05:33 AM.

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#21 Veridian

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Posted 16 June 2021 - 03:29 AM

   Once the round-nut was removed, a mark was placed on its top side with the blue Sanford marker. The outer, top side of the machined washer beneath was cleaned off with a little isopropyl alcohol on a q-tip and another mark made with the Sanford. 

   The side-arm assembly and hood for the box could now be carefully lifted from the base. Turning the slow-motion knob, while gently lifting the side-arm, helps to it free up and prevent damage and burrs from ending up on the worm and ring gear beneath the hood.

   The thrust bearing assembly (needle bearing and two machined washers as races) could now be tipped out into my hand. The 3 bearing assembly parts should not be mixed up, so I was careful to keep these three parts together respectively and set them aside on a clean sheet of paper.

 

   The thrust bearing consists of an inner, hardened steel, needle-roller cage assembly with a matching, hardened steel, pair of precision washers that are the top and bottom races. Should these parts ever need replacement, McMaster-Carr is one source for the bearing and washers.

 

The needle-roller cage assembly measures:

15mm  shaft diameter (ID)

28mm  outer diameter (OD)

2mm    thickness

 

The 2 hardened steel, precision washers measure:

15mm  shaft dia.(ID)

28mm  OD

1mm    thick.

 

Attached Thumbnails

  • rps20210615_054527.jpg
  • StarPro AZ; azimuth contrl. thrust bearing.jpg

Edited by Veridian, 16 June 2021 - 04:06 AM.

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#22 Veridian

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Posted 16 June 2021 - 03:44 AM

The side-arm and hood as removed from the mount.

 

In the bottom photo, a transparent, plastic, shim washer can be seen as marked with a blue dot and being slightly lifted with a scribe.

 

The red dots mark the location of the set-screw (grub screw) on the worm block and an access hole I drilled in the plastic hood.

 

The plastic hood is secured to the cast aluminum side-arm with 3, phillips head screws (120° apart) and the 2 allen screws that fasten down the worm block.

 

 

Coming up next, the azimuth clutch assembly.

Attached Thumbnails

  • StarPro AZ; azimuth hood, worm, thrust brng..jpg
  • StarPro AZ; azimuth cntrl. worm & block.jpg

Edited by Veridian, 16 June 2021 - 04:01 AM.

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#23 Veridian

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Posted 17 June 2021 - 02:53 AM

   Before going any further with the azimuth clutch assembly, I need to stop here and make some clarifications on the altitude clutch assembly and adjustment, as well as point out an important omission in the instruction manual for the Meade StarPro AZ series of telescopes. The clarifications that need to be made are in posts 6, 7 and 8 and are specifically regarding the adjustment of the large, round-nut that functions as the inner, clutch pressure plate.  I also forgot to include photos showing the hub axle (driveshaft) and related parts, as well as the stop pin on the altitude side-arm.

 

   Overall, I have been quite satisfied with my StarPro AZ 70mm and 90mm. In many ways, these telescopes have been appearing too good for their price and somehow this makes me suspect that there must be a flaw somewhere in the design, materials, or assembly. I did find some minor issues, but nothing that can not be readily taken care of. That is, until today. I found something that unless it is paid some attention, it is going to cause problems for this series of telescopes and be a headache for Meade's warranty department. 

   

   In brief, the altitude control MUST have its clutch disengaged, before operating in free scan mode. Not disengaging the clutch will eventually cause the large round-nut (with 2 holes and 3 set-screws) to loosen and the slow-motion control to fail operating. When this nut loosens up, the 3 set-screws will then begin to damage the threading on the axle and if not promptly addressed, the axle threading will be ruined. In the Meade Instruction Manual, I was unable to find any mention of first loosening the altitude clutch, before operating in free swing.

   I had complained about my 70mm being too loose in the free swing mode with the clutch disengaged. In fact, this indeed needs to have fully free movement and "drooping" is to be expected when the optical tube assembly is not in balance and unclutched. When changing out eyepieces, or the diagonal, the clutch knob should first be snugged up and then the change made. Not difficult and a simple added step. I had assumed some drag on motion in free swing (clutch disengaged) would be preferrable. Not so.

   Unfortunately, at this time, I am unable to do any editing of these initial posts. 

 

Photos and further explanation, clarification and diagnosis will follow in the next 2-3 posts.


Edited by Veridian, 17 June 2021 - 03:09 AM.

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#24 Veridian

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Posted 17 June 2021 - 06:13 AM

   The altitude side-arm casting is seen here with the hub/axle (driveshaft) and clutch assembly removed. 

   The pin (next to red dot) is the stop for elevation and declination and matches to the long slot in the hub. [more on this later on]

Attached Thumbnails

  • StarPro AZ; alt. side-arm w-o hub & clutch asy.jpg

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#25 Veridian

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Posted 17 June 2021 - 06:29 AM

   Here is the full spread of the internal parts attached to the altitude side-arm. The allen wrench is set between the hub/axle and the round nut (inner pressure plate) to show where the side-arm separates the complete assembly.

 

red dot    Hub & axle (driveshaft). White, nylon washer meas: 34mm OD × 20mm ID × 1mm Thk.

 

orange    Round-nut (inner pressure plate).This is the problem part.

                The white, nylon friction washer measures the same as the one on the hub.

 

yellow    Fiber friction washer. Meas: 37.5mm OD × 16mm ID × 1mm Thk.

 

green     Worm ring-gear. Meas: 41mm OD × 14mm ID × 6mm Thk.

 

blue        Two, outer, nylon washers. Meas: 30mm OD × 14mm ID × 1mm Thk.

 

indigo    Outer pressure plate (the "pork pie hat")

 

 

    With the exception of the hub and axle, as well as the roundnut fastened to the axle by its 3 set screws, when the the altitude clutch knob is disengaged (loose) all of the rest of these parts turn free on the hub's axle (drive shaft). 

    Tightening the clutch knob engages the free floating parts (worm ring gear between the nylon and fibre washers, and the "pork pie hat", outer, floating pressure plate) when being pressed together as a single unit and against the roundnut that is anchored by its 3 set-screws upon the axle. Tightening the knob allows the worm's ring-gear - now pressed tight against the fixed roundnut - to turn the axle/driveshaft. As the gear teeth on the worm (the slow-motion control) are passing through the teeth on the worm's ring-gear, the axle turns.

   By re-reading the previous 2 paragraphs you will catch the fact that all of the pressure and engaging torque on the altitude control centers upon the 3 set-screws that fasten the inner pressure plate (the roundnut) to the axle/driveshaft. Herein lies the problem, as I see it.

 

   Indications and diagnosis of the problem with the roundnut and an explanation of adjustments will soon follow.

 

   

Attached Thumbnails

  • StarPro AZ; alt. hub, axle, clutch assembly.jpg

Edited by Veridian, 18 June 2021 - 02:16 AM.

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