20 replies to this topic

[moladso]

The extremly beautiful, finely machined Carton CST equatorial mount has an unusual locking mechanism, based on a clamp that brakes the axis with a double knob.

 

 

My problem is that the clamp slides and does not lock the axle completely. Both axles are a little free. I rule out mechanical breakage or wear because the mount have been very well used, it's as new, so I think it may be a problem of grease in the mechanism or just internal adjustment.

 

 

 

I suppose it's a common problem with this mount, but CSTs are very rare so I haven't found how to take the axle apart and adjust the locking mecanism. A peculiarity of this mount is that both axes are machined identically, they are practically interchangeable..., so my problem is multiplied by two..

.

 

As always happens with classic telescopes, the risk of breaking something when trying to dismantle it without experience is very high and the consequences of not doing it correctly may be catastrophic.

 

Does anyone here have experience on how to solve this problem or how to dismantle the axis and locking mechanism?

[jkmccarthy]

My problem is that the clamp slides and does not lock the axle completely. Both axles are a little free. I rule out mechanical breakage or wear because the mount have been very well used, it's as new, so I think it may be a problem of grease in the mechanism or just internal adjustment.
 
I suppose it's a common problem with this mount, but CSTs are very rare so I haven't found how to take the axle apart and adjust the locking mecanism. A peculiarity of this mount is that both axes are machined identically, they are practically interchangeable..., so my problem is multiplied by two..
.
As always happens with classic telescopes, the risk of breaking something when trying to dismantle it without experience is very high and the consequences of not doing it correctly may be catastrophic.
 
Does anyone here have experience on how to solve this problem or how to dismantle the axis and locking mechanism?

Hi !
 
I have no direct experience (yet) regarding how to solve this problem, but I can sympathize as I have the same Carton mount (only finished in black and re-branded/re-sold by TeleVue as their Renaissance Systems Mount -- RSM or sometimes RSM2000).   So I'm likewise very interested in discussing/deciding how best to proceed.   The following may provide us [and others here who may wish to weigh-in with ideas/recommendations] some food for thought:
 

[...] I thought I'd share this link describing (in too little detail, sadly) the teardown and refurbishment of a TeleVue [re]branded CST -- in case you haven't already run across it yourself:
 
http://darkerview.co...dpress/?p=18299

... In particular, note this text from the on-line blog description:
 

The clutches were an issue as well. These are a band clamp
arrangement that clamps the shaft to the worm gear.  This
prevents any motion of the axis other than rotating the worm.
Two metal tabs protrude from the housing; squeeze them
together with a screw, and the clamp tightens.  Unfortunately
the thick tabs [can become] slightly bent, [and so] tightening
them all the way still allows a bit of movement.   To solve this,
I filed away just a little bit between the tabs to give them a
few thousandths more adjustment.

[emphasis added is mine].
 
Now regarding the blog-author's stated fix, which for starters requires a teardown to remove the band clamp, is that he proposes using a file to remove material from the tabs on the band clamp (in order to enlarge the gap between the two tabs that have become bent-inward, towards each other) ... my concern is that by filing away material to enlarge the gap, the blog-author is meanwhile making the tabs thinner, which I worry will make the tabs more susceptible to bend-inward again in the future.  So when the inward-bend returns and more filing becomes necessary, this becomes a downward spiral ....

 

Instead, I've been "mulling-over" in my head ideas for how to simply just reverse the inward bend of the band-clamp tabs, without removing any material that would end up making them thinner.

 

What if a small shim or wedge were temporarily inserted between the exposed tops of the tabs with the clamping knobs loose (so the shim or wedge would push then the tops of the tabs apart), and then the clamping knobs were tightened-down, either moderately hard or very hard ?  (I'd be inclined to try just moderately hard first !).  Doesn't it seem reasonable to imagine that this would achieve the desired result of correcting the inward-bend of the band-clamp tabs (now unfortunately towards each other), and either straightening-out the tabs or else leaving the tabs with a slight outward-bend instead ?

 

The biggest risk I see in trying to use a shim between the tops of the tabs to achieve a fix is that instead of going from tabs bent together like this // \\ to ideally straight tabs || || or else tabs bent apart like this \\ //  ... is the risk that instead the tabs would end up being bent together like this:  )) ((  ... where the shim/wedge inserted temporarily at the top creates the desired outward bend (but *only* at the very top), and unfortunately the bottom (inside) ends of the tabs might still remain bent apart(?) at the bottom, since the knobs where I'd be applying the clamping./bending force is at the mid-height of tabs.

 

Note that at the bottom is where the shaft is located that we want the band-clamp to tighten around ... so tabs shaped like )) (( might be no real improvement in the clamping force that the knobs are able to apply around the shaft inside the housing.

 

The chance I'd end up with tabs bent apart at both top and bottom is what's (so far) kept me from giving this a try.  My latest thoughts are that the shim/wedge idea (with the clamping knobs loosened, or even removed) is probably(?) 'the right idea' ... but forcing the tabs together --- with the shim/wedge temporarily in place --- using the clamping knobs  (at the mid-height position on the tabs)  might not be the best idea.  Much better I think would be to engineer some "pincer" clamp jaws that could reach down into the housing to the bottom, where the outside face of each tab meets the band that surrounds the shaft, and *force* the base of the tabs together at those locations (to give this result:  \\ // ...) instead of forcing the tabs together using the clamping knobs (that could(?) end up with this result:  )) (( ...).  

 

I welcome others thoughts and comments on this problem and how best to approach a solution !

 

Thanks,

 

       -- Jim

 

P.S.  I think the likely root cause of my mount's problem is all the weight I ask it to carry with my SkyWatcher 180mm MCT attached ... exacerbated by the multiple adapter plates underneath the dual Vixen/Losmandy dovetail clamp saddle I'm using, that push the OTA center-of-mass even farther out from the R.A. axis, requiring even more counterweight.  https://www.cloudyni...e-rsm-eq-mount/  Attaching the OTA closer-in somehow would definitely be an improvement in that regard ... not to mention being even more picky about precise balancing, so that clamping around the R.A. axis wouldn't require a full 1-McCarthy of torque to be applied !

 

[jkmccarthy]

FYI, here's an Instagram post (with no accompanying 'howto' narrative, unfortunately) that shows a Carton Supernova / TeleVue RSM2000 mount disassembled into its constituent pieces:

 

https://www.instagra.../p/BBMt11BuLYu/

 

R.A. axis partially reassembled here:  https://www.instagra.../p/BBPpQ22uLSY/  ... all primed + repainted in a Takahashi-matching green color ... https://www.instagra.../p/BBMdXuAuLRL/

 

_______

 

Looking again at how long those band-clamp "tabs" for the axis clutch are, I'm now wondering if inserting shims or wedges between the tabs and the slot-opening for the tabs in the cylindrical housing, and with the tabs held/forced as tight against each other as possible at that below-knob-height (i.e., where the tabs exit the cylindrical housing), maybe then tapping a razor-thin wedge between them down from the top would do a better job of reversing the bent-inward // \\ problem with the tabs, being less likely to result in the convex-bent tabs )) (( that I've been worried about if trying to force them together using the clamping knobs located at  mid-height ?

 

((My description above probably fails to capture the proper time-sequence of getting wedges in-between the cylindrical housing slot-edges and outside-faces of the tabs and likewise between the two inside-faces of the tabs at the top --- seems like it would be necessary to get all these wedge-shims "started' first, before trying to force any of them to be *tight* --- and likewise necessary to keep in mind that the goal is to reverse inward-bends of the tabs that might be measured in "thousandths of an inch" only ... meaning the goal is *not* to introduce significantly larger bends in the opposite direction !    Easy does it ? ....))

 

Comments welcome,

 

        -- Jim

Edited by jkmccarthy, 05 November 2023 - 06:12 PM.

[deSitter]

I would use a shim made from a beer can to tighten this up. Make a little lip so it stays put.

 

-drl

[jkmccarthy]

I would use a shim made from a beer can to tighten this up. Make a little lip so it stays put.

 

-drl

That shim would be installed 'permanently' (?) between the tabs at the top?  When the knob is tightened and the shim stops the tops of the tabs from contacting each other, you expect that further tightening the knob will pull the bottoms of the tabs together (more than happens now without the shim) such that the clutch clamp-band tightens better around the shaft ??
 

[deSitter]

That shim would be installed 'permanently' (?) between the tabs at the top?  When the knob is tightened and the shim stops the tops of the tabs from contacting each other, you expect that further tightening the knob will pull the bottoms of the tabs together (more than happens now without the shim) such that the clutch clamp-band tightens better around the shaft ??
 

Yes. Cast aluminum doesn't bend - it cracks. You'd really need some separation and force to cause cracks, and then it would just completely fail to hold. I suspect that use has just milled down the aluminum and you could almost surely just file down the "ears" to get more purchase, but shims will also work.

 

I'm simultaneously full of admiration and frustration at Japanese engineering. Here again is a single point of failure, which makes the mount unusable in the event. The best idea is a brass plate to impinge on the drum/shaft which can be tightened down as much as necessary and never cause any trouble.

 

-drl

[jkmccarthy]

drl --

 

The sketch below shows the cross-section of rail clamps (green, one each side) that I designed & built long ago to hold a sliding plate (light blue, top) to a fixed baseplate (darker blue, bottom), where the black vertical centerlines mark the locations of the clamping bolts through each rail that thread into tapped holes in the baseplate.

 

 

The small bump-strip on the outside bottom edge of each rail clamp was designed so that when the clamping bolts are tightened, the bump-strip would become a pivot-point and the inner portion of each clamping rail would then tilt inward, which very effectively transfers the bolts' clamping force to the inner portion of the rail clamps so they push down very well on the top of the sliding rail.

 

So yes, turning my head sideways and imagining the green-shaded rail clamp is one of the Carton CST band-clamping "tabs", I can appreciate the logic + insight behind your idea to use a permanent shim (analogous to the bump-strip in this concept) between the tabs at the top to create a pivot-point so the CST's clamp-band knobs more effectively push the bottoms of the tabs together to clamp more tightly around the shaft.

 

Great suggestion / idea --- I'm looking forward to giving it a try on my TeleVue RSM (Renaissance Systems Mount) re-brand of the Carton CST !

 

Thanks much,

 

        -- Jim

Edited by jkmccarthy, 06 November 2023 - 12:32 PM.

[moladso]

Thanks all your comments and proposals.

 

My idea is to remove material from the inner face of the contact point obliquely, so that the clamp pressure is increased.

In essence it is the same principle that jkmccarthy and deSitter propose, a fixed shim, but using the clamp itself.

 

 

The problem I see here is that you have to remove the clamp because otherwise metal debris will penetrate inside the mount mechanism, causing damage.

 

That's why the very first thing to do is to find out how to disassemble those axles. It appears that the author of the aforementioned blog uses a self-built tool to loosen the shaft, but it is unclear to me how he does this.

 

Edited by moladso, 06 November 2023 - 05:07 PM.

[tturtle]

As noted, it looks like you would really want to disassemble the clamp and shaft before filing down the tabs to avoid getting metal filings inside the mount.  In this case I would try an alternative approach where you add a very thin metal or even plastic “shim tube” to the inside of where the clamping ring contacts the shaft. You could even probably glue some very thin metal or plastic to the inside of the clamping ring. This is a safer way to increase the clamping force on the shaft. I think you may be chasing your tail by filing down the tabs and as noted this may weaken the tabs.

Attached Thumbnails

• 

Edited by tturtle, 07 November 2023 - 05:15 AM.

[moladso]

I have found a not perfect but easy solution for this problem.

Published here for your study and comments: https://www.astronom...152&id_prod=580

 

 

 

[jkmccarthy]

I have found a not perfect but easy solution for this problem.
Published here for your study and comments: https://www.astronom...152&id_prod=580
 
IMG_9693.jpg

Interesting idea ... thank you moladso for sharing this blog post !    (Others here on CN might also enjoy the blog-author's post on his Carton CST-100KX kit, which I found here:  https://www.astronom...151&id_prod=544 : - ).
 
But what really caught my eye were these photos from the blog post you shared ... the first illustrates extremely well the "problem condition" where the clutch clamping tabs are pushed-together tight by the clamping knob, but inside the housing the ends of the tabs are still separated by a considerable gap where they extend out from the clamping band that surrounds the shaft* ... (the first photo below leaves no doubt as to the cause of the problem ... and also shows the tabs' problematic length::thickness aspect ratio that adds to our difficulty given how far outside the clamping bolt + knobs exterior to the housing are located  ) - : 
 

 
But even more interesting to me is another of the blog-author's photos, that shows this view from the underside of the housing (i.e., the underside where the Decl housing connects to the top of the polar axis, or equivalently the underside where the R.A. housing connects to the top of the latitude-adjustment base):
 

 
This second picture especially makes me wonder whether there is sufficient "access" through the underside opening (perhaps in tandem with access through the port on the top side, through which the first picture above was taken) to actually implement tturtle's sugggestion in post #9 to "add a very thin metal or even plastic “shim tube” to the inside of where the clamping ring contacts the shaft. You could even probably glue some very thin metal or plastic to the inside of the clamping ring. This is a safer way to increase the clamping force on the shaft."   IF (?) this shim could be added working through the underside opening --- rather than requiring a complete teardown to remove the clamping ring from around the shaft* --- would this change our ideas on the first fix to be attempted ?
 
Obviously without removing the axis from the housing, tturtle's suggested "shim tube" would need to be a rectangular strip of shim stock inserted between the shaft* and the clamping ring, such that the shim would not be a closed tube but would instead end up being at best C -shaped ... say, with its open end underneath where the clamp itself has a gap between the two tab connections ... but after removing the knobs and threaded clamping bolt, would it become possible to push the ends of the clamping ring far enough apart to feed a shim strip in through the underside opening and install it between the clamping ring and the shaft* ?   I realize that the thinner the shim material is, the more difficult it becomes to "push" on it so as to move it into the desired location, without it just wrinkling up and compressing into a wad instead of moving where we want it to go.   That fact, plus the fact that the space created between the clamp ring and the shaft* will only be X / 2pi, where "X" is whatever increase in separation one manages to create temporarily in the split-ring clamp by pushing the tabbed ends farther apart ... and "2pi" obviously is 6.28 ... meaning it would require an extra 1/16th of an inch increased separation at the ends of the split ring clamp to create temporarily a 10-thousandths-of-an-inch radial gap between the ring I.D. and the O.D. of the shaft* into which to maneuver [say, a 0.003" or 0.004" thickness?] strip of shim material into a C-shape around the shaft* without having it all just crumple-up on you ...
 
Thoughts ?
 
        -- Jim
 
EDIT:   *Actually, I think the clamp (speckled blue cast aluminum in the second photo) actually surrounds a thick-walled cylindrical tube [with the yellowish-orange chamfer around its outer circumference] that extends inward from the worm gear, and not the [darker in color] innermost axis "shaft" itself ... such that the shim suggested by tturtle would need to go between the I.D. of the clamp and the O.D. of that inward-extending thick-walled cylindrical tube with the yellowish-orange rim ... that is, *not* between the I.D. of that thick-walled tube and the O.D. of the dark-in-color shaft.

Edited by jkmccarthy, 10 November 2023 - 03:56 AM.

[tturtle]

 

That picture does clarify that the problem lies with the fact that the tabs through which the clamping force is applied are probably too flexible and there is a risk that if you file them down they will be even more flexible and may even break when you tighten it (depending on how much material you remove).  This clamping ring should have been made of a much stiffer material and not the cast aluminum which is known to be somewhat soft.  I would find a way to insert the shim.

Edited by tturtle, 10 November 2023 - 03:55 AM.

[moladso]

Thanks for all your comments.

 

I also tried to simulate inserting a spacer between the clamp tips. I started with a 0.5mm shim up to 1.0mm. The effect is what jkmccarthy had already predicted: the tips arch without a perceptible effect on the pressure exerted by the clamp at its point of contact with the saddle's gear.

 

 

I have modified the blog to document this test.

 

Once we reach this point, for me the only viable alternative is to completely disassemble the mount and apply one of these solutions:

- Straighten the tips of the clamp: temporary solution, because sooner or later they will bend again.
- Insert a shim between the clamp and the gear: I think it is also a temporary solution but somewhat more durable than the previous one.
- Manufacture a new clamp using an stiffer material than the cast aluminum used, which is like butter. It is the definitive solution, but complex and expensive.
- Finally, a solution that I don't like because it means modifying a classic jewel with no guarantee of success: drill a threaded hole in the flat side of the casing and mount a "classic" brake system.

 

To disassemble the mount it's needed to remove the slotted lock nut on the axis. Now I understand the tool that is needed. I have to check if it corresponds to any measurement of the DIN 981 standard with tools KM0 to KM20 (removing one pair of pins).

 

 

 

 

 

There is still a simple, non destructive and economical alternative to test, without disassembling the mount: replace the current screw steel bushing with another one with a stiff steel plate welded at 90º angle, which will help to divert part of the screw pressure to the base of the clamp tips, as shown in this picture and drawing. I honestly don't have much confidence that this will work, but a test would be worth it.:

 

 

 

At the moment the installed brake screws seems to improve the locking of the mount a little, but it is not a good solution.

Edited by moladso, 10 November 2023 - 07:44 AM.

[Exnihilo]

I have the Televue version of this mount, and it has a single bolt clamp on both axes.  I'm having problems with clamping on the RA axis, however.

[CHASLX200]

I always wanted one of them mounts but scared off now.

[jkmccarthy]

Thanks for all your comments.
 
I also tried to simulate inserting a spacer between the clamp tips. I started with a 0.5mm shim up to 1.0mm. The effect is what jkmccarthy had already predicted: the tips arch without a perceptible effect on the pressure exerted by the clamp at its point of contact with the saddle's gear.
 
IMG_7083b.jpg
 
I have modified the blog to document this test.
[...]

Hi moladso --

 

Thank you for pursuing this idea and reporting back here with your findings ... sorry to learn this approach did not result in any improvement : - (

 

May I ask, how far down (toward the clamping bolt that runs between the knobs) did your 1mm metal shim extend in the test shown in the first picture in post #13 ?   With reference to my plate-clamping sketch in post #7, the metal shim at the outermost tip of the CST clamping tabs needs to function as a pivot-point ... if the shim extends too far inward (and in the limiting case, extends in far enough to almost touch the clamping bolt), then there will be no "lever arm" between the bolt and the pivot point, and no clamping force applied around the worm gear's hollow shaft when the knobs are tightened and the tabs clamp around the metal shim.   But maybe it's not too surprising that even with just ~ 2mm or 3mm of shim insertion between the tops of the tabs, the ratio of "lever arm distances" from shim-pivot-to-bolt -vs- from shim-pivot-down-to-tab-connections-to-clamp-band around the hollow shaft is not favorable in terms of geometry, given the soft cast aluminum tabs which are not stiff enough to transfer adequate force from the clamping bolt down to the clamp band without bending.

 

Meanwhile I should apologize for not realizing -- in my post #11 above -- that YOU are the author of the blog you cited in post #10, and that is YOUR web-site and CST-100KX.  Very very nice (!!).  ((And likewise thank you for sharing  on your blog site the small collection of classic Vixen catalogs as PDFs, several of which I had not run across previously on the web....)).

 

 

[...]
Once we reach this point, for me the only viable alternative is to completely disassemble the mount and apply one of these solutions:
- Straighten the tips of the clamp: temporary solution, because sooner or later they will bend again.
- Insert a shim between the clamp and the gear: I think it is also a temporary solution but somewhat more durable than the previous one.
- Manufacture a new clamp using an stiffer material than the cast aluminum used, which is like butter. It is the definitive solution, but complex and expensive.
- Finally, a solution that I don't like because it means modifying a classic jewel with no guarantee of success: drill a threaded hole in the flat side of the casing and mount a "classic" brake system.
[...]

Regarding options 1 and 2, any guess as to how much "later" before the problem will return in the true statement that it will come back "sooner or later" ?   If the original design worked more-or-less-okay for 20 years after manufacture, and only now (after 30 to 40 years) we are experiencing problems, well ... ?    (Of course we don't know how many clamp-and-release cycles a given mount would see in a given decade, so maybe it is hopeless to speculate about how long a 'temporary' fix would last ...).

 

Another approach (that might appropriately be placed third(?) in your ranked list above) would be to use the existing clamping band and its tabs, but to relocate the clamping bolt further down on the tabs ... so that the ferrules around the clamping bolt just barely clear the outside surface of the band clamp. Obviously this would require drilling *two* new holes in the side of each axis housing for the clamping bolt and (new, longer?) ferrules to extend beyond the housing.  But I would have to imagine that having the clamping bolt apply the clamping force much closer to the band-clamp would eliminate "bending of the tabs" as a factor causing the design to fail after many years.   Here's a notional cartoon to illustrate this idea:

 

 

Not to say that the `` *two* new holes ` ` would be easy to drill at such a shallow angle.  Slots instead perhaps ??   (However, the Carton Supernova / TeleVue RSM mounts have previously received criticism for having axis housings which are not sealed against intrusion of dust + debris, and "slots" to allow the modified (lowered) clamping bolt to escape the axis housing would only make the axis housing more susceptible to such intrusion.

 

But might it be possible to replace the present long clamping bolt and ferrules and knobs with just a hex head bolt and a hex nut, and have flat bicycle wrench style "levers" come up out of the housing alongside the tabs, such that one could tighten and release the clamps by pushing the "levers" forward or backward (granted there might only be 1/6-th of a turn possible for the lever on each side).  Here's a second cartoon to illustrate:

 

 

It's not immediately obvious (not even to me : - ) how these bicycle-wrench -type levers could be installed and mated to the hex head(s) of a new nut-and-bolt pair to replace the existing long clamping bolt and knobs, and once assembled obviously the levers would need to be positioned "Just So" they could go from *clamped* to *released* within the narrow (1/6-th up to ?maybe? 1/4-th of a turn) available tilt angle range based on the existing cut-out at the top of the axis housing for the existing tabs.  Note that I'm simply brainstorming here, so kindly excuse any / all ideas tossed-out here that are only "half-baked"  ....

 

[...]
To disassemble the mount it's needed to remove the slotted lock nut on the axis. Now I understand the tool that is needed. I have to check if it corresponds to any measurement of the DIN 981 standard with tools KM0 to KM20 (removing one pair of pins).
 
IMG_7091s.jpg
 
KM-0.jpg
 
81SS3oA2L6L._AC_SL1500_.jpg
[...]

It's likely you've already reached the same conclusion, but my hunch is that each of the two hex shafts rising vertically from that home-made fixture (seen in the second photo of your post #8) have screwdriver blades on their bottom ends, and the round-headed bolts seen at right angles to the hex shafts are grub-screws to hold the screwdriver blades at the bottom ends aligned properly and at the proper height (depth) to engage the slots on the retaining ring of the mount's axis. 

 

[...]
There is still a simple, non destructive and economical alternative to test, without disassembling the mount: replace the current screw steel bushing with another one with a stiff steel plate welded at 90º angle, which will help to divert part of the screw pressure to the base of the clamp tips, as shown in this picture and drawing. I honestly don't have much confidence that this will work, but a test would be worth it.:
 
IMG_7080b.jpg
 
Image1.jpg
 
At the moment the installed brake screws seems to improve the locking of the mount a little, but it is not a good solution.
[...]

Yes, my brainstorming has also considered similar ideas ... the problem is that the width of the existing (soft metal) tabs don't leave much free space available for any really *stiff* steel plate to fit against the exterior of the tab.  Rather than a semi-circular concave end, wouldn't we really want a slightly wider plate able to accommodate a circular hole so that it could be welded to the ferrule on bottom *and* on top ?   Where my imagination gets "stuck" on this concept is how little clearance the ferrule would need to have around the clamping bolt to prevent the ferrule (and the attached stiffener plate) from simply taking-on a "tilt" that matches the angle of the bent tab(s) .... 

 

Anyway, maybe some half-baked idea here will stimulate you (or the others who are following this thread) to think of some more promising / less invasive idea ?   I'll certainly be continuing to mull this over myself ....

 

Cheers,

 

       -- Jim

Edited by jkmccarthy, 10 November 2023 - 11:11 PM.

[jkmccarthy]

Here's a "right- and left- handed double-ended threaded stud" that could be used -- and in fact I think a stud of this type would be very advantageous in this application:

 

https://belmetric.co.../?sku=SRL6X65SS

 

With clearance-holes drilled through the tabs, and with appropriately-matched left- and right- threaded nuts exterior to the tabs and bicycle-wrench style levers mated to each of the nuts, the two positions for "clamped" and "released" would then become either "both levers forward" or "both levers backward" (depending on which way the double-ended threaded stud is installed).   Also, I think what makes such an opposite-handed double-ended threaded stud ideal for this application is that it provides a given amount of clamping/release separation-between-the-nuts in _half_ the angular stroke of the levers (which is a significant advantage here because the slot through the top of the housing limits the amount of angular stroke available for the levers' range-of-motion), compared to copying the existing continuously-threaded clamping bolt arrangement.

 

It also occurs to me that one really would *not* want to go too big on the diameter of the threaded stud / bolt selected, since the larger the diameter of the hole one drills through the tabs, the weaker the tabs become (structurally-speaking).  But for ease of clamping with levers that are restricted to a limited stroke, coarser threads would be preferred over finer threads.

 

((As an aside, if one were able to epoxy the bolts to the exteriors of the tabs, it's conceivable the "bicycle wrench" lever could be placed between the two tabs --- if that gap were wide enough (and/or the lever were thin enough).  The stud offered at the link above appears to have flats cut on two opposing sides of its middle section (for a crescent wrench), so conceivably with a metal file one could create four more flats to give the middle part a hexagonal cross-section)).

 

As far as installation is concerned (and regardless of one lever between the tabs, or two outboard levers), I now realize that the clamp mechanism can be (temporarily) installed around the thick-walled cylinder extending inward from the worm gear --- outside of the axis housing --- for the purpose of fine-tuning (prior to installation into the mount) whatever nuts and clamp "levers" one finally decides upon, in order to find the borderline sweet spot between clamped and released, and then secure (epoxy?) the levers onto the nuts so the levers are in the desired vertical "neutral" position at the sweet-spot in-between clamped and released.  Note there is a top section of the axis housing (forward of the where the tabs emerge from the housing) that is separate from the housing itself, so the opening for the tabs (and my lever(s) alongside or between them) is really a slot that allows the clamp (with levers attached and pre-tuned to the clamp/release borderline sweet-spot) to be installed into the forward portion of the housing, before the worm gear and its thick-walled cylinder are then re-inserted (and likewise the shaft that extends all the way out the rearward portion of the housing where the slotted collar is then threaded onto the shaft and adjusted for optimum axial preload of the bearings.

 

So personally I think a short clamping bolt installed at the base of the tabs, with bicycle-wrench-analog levers to tighten & loosen nuts for clamping/releasing rotation of the axis, can be made to work without needing to modify the axis housing ... the only modification needed would be to drill through the clamp-band's tabs just above where they attach to the clamp-band at their base.  If the "solution of last resort" is to custom-machine replacement clamp bands and tabs out of a stronger/stiffer material, then ultimately the original clamp bands will get replaced/discarded anyway ... so nothing to lose by (no regret over) drilling an extra hole through the each tab near its base ??

 

       -- Jim

 

P.S.  And with respect to my second cartoon in the previous post, given an opposite-handed double-ended threaded stud, I suppose there is no reason why the two small cylindrical handles I sketched at the end of each lever oriented away from each other couldn't be replaced by one longer cylindrical handle connecting the tops of the levers together (as long as the two levers are long enough that the cylindrical handle connecting them clears the tops of the existing tabs : - ) if one prefers a design that's less likely to snag a cable.   Although I guess a single cylindrical handle might increase the chance of getting a finger pinched between the bottom of that handle and the tops of the existing tabs ?  Off hand, I'm not yet certain which style might end up being the best overall.

 

Another question I've still been pondering is whether such an opposite-handed double-ended threaded stud can be allowed to "float" within a clearance hole through both tabs --- in order words, how does one ensure that over repeated clamping+release cycles (operated by CW and CCW movement of opposite-handed nuts attached to the ends of levers on each side), the stud itself doesn't incrementally rotate -- or "walk" if I can be allowed to mix metaphors here -- until eventually the nut on one side unscrews off the end of the stud ?   I *think* the answer is, one would really want to epoxy (or "loctite" ) one of the nuts to the threaded stud on one side ... and that doing so doesn't actually impact the operation at all.  When both levers are moved, if the motion of one lever turns the threaded stud and the motion of the other lever turns the opposite-handed nut on the other side, one still gets double the change in separation between the nuts (as before, when I was imagining the stud would "magically" be stationary and each lever would rotate an opposite-handed nut on the stud).  And with one nut locked to the stud, there's no longer any risk that after repeated clamping+release cycles the nut locations on the stud would change over time.  Anyone disagree?  

Edited by jkmccarthy, 11 November 2023 - 02:08 AM.

[Exnihilo]

I have the Televue version of this mount, and it has a single bolt clamp on both axes.  I'm having problems with clamping on the RA axis, however.

Interestingly, I reversed the RA clamp bolt and the problem was fixed.  

[moladso]

Interestingly, I reversed the RA clamp bolt and the problem was fixed.  

Very easy to apply, will give it a try...

Edited by moladso, 28 November 2023 - 01:08 PM.

[56S]

Would installing a stout flat washer between the bolt and each side of the clamp help move the clamping force inwards?

[Taygeta]

hello

 

End ?