Re: Relationship between needle bearing wobble and variable worm mesh and backlash
So the G11 axis has a radial bearing surface for the ring gear mechanism after all?? Well, never mind what I said, then.
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Re: 76sec error on new OPW-11
Jim can you share your guidelogs or PE analysis data files?
I purchased the one piece worm from Losmandy hoping to get rid of some of my errors.
So far my 76 sec is worse than ever, and my PHD2 rms got worse.
I snugged the bolts for the worm block to worm housing first, then slightly snugged the bolts to the mount.
I then slightly loosened the worm block bolts to allow them to center with the worm, and then tightened them.
I've tried twice now and still get the same result
There's no noticeable backlash and it seems to run smooth, but obviously something is wrong.
The immediate thought is the worm blocks are "twisting" somehow and putting side load on the bearing.
Since I got almost the same results after R&R the assembly I wonder if the housing was drilled/bored off center.
Appreciate any help and input.
Thanks
Jim P
-- Brian?
Brian Valente portfolio
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
Hi gang,
I want to correct something. That is, whether the ring gear has its own cylindrical needle bearing or not.
It turns out that the G11 has one and the GM8 does not.??
The removal of the cylindrical needle bearing from the design is how the GM8 got "shrunk" from the G11 design.??
Here is what I find in my GM8 and G11 versions.??
(Yours may be different: a new G11 I looked at has a ring gear that was black, and likely anodized black aluminum.? My G11 has a ring gear that looks like steel, and is nonmagnetic. The upper thrust bearing and it's races are placed under the ring gear is loosely centered around an aluminum boss.? )?
? Element? ? ? ? ? ? ? ?GM8.? ? ? ? ? ? G11 Composition? ? ?Aluminum.? ? ? ?Steel appearance ?Magnetic?? ? ? ? ? ? ?No.? ? ? ? ? ? ? ?No ? Has a cyl? needle bearing?? ? No.? ? ? ? ? ? ? Yes Teeth.? ? ? ? ? ? ? ? ? ? 180.? ? ? ? ? ? ?360 ?Worm period.? ? ? ?480 sec.? ? ? 240 sec Clutch disk OD.? ? ?3.0 in.? ? ? ? ?4.25 in.
When the RA is driven at high speed slew, the GM8 sounds louder than the RA axis.? If the maximum speed of rotation (degrees per second) are identical in a GM811, the GM8 axis should be driven by the gearbox? half as fast on the GM8 axis as for the G11 axis.??
The Gemini-2 handset shows one digital speed setting, so that seems to be used for both axes.? It really should have the digital speed for each axis set separately.? The software could easily be coded to split these out.??
If you have a GM8 mount, the RA will not only have the coarser 180 tooth ring gear, that ring gear will be rotating around a metal cylinder, not a rolling bearing.??
The G11 ring gear has 360 teeth, is (nonmagnetic stainless) steel, with a cylindrical needle bearing inside, rolling on the metal cylinder.??
?
Michael,
the shaft and the round plate on its end are definitely aluminum. Its weight is inconsistent with
a different material i.e. stainless steel. The areas with wearing signs (discolored) are fairly smooth
under finger touch, no scoring anywhere, but nevertheless, following your suggestion, I checked the
thrust bearing and the two washers just before the clutch knob, and they are fine and smooth, BUT, the spring washers
of both axes have serious burrs internally and are potentially dangerous to touch, so that might
explain the markings in that area of the shaft, although this doesn't cause problems on the DEC axis.
Anyway I removed the two spring washers and was more generous with grease on the thrust bearings
and the result of this is that the grip now is better than before and the overall stiffness is higher.
Thank yo so much for your precious hints.
Sandro.
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
Don't the "touch points" as per Peter's drawing, depend on how the scope is balanced? If the scope is balanced towards the counterweight, these touch points would be just opposite.? And if the balance were perfect the touch points would be on the same side (low).
Based on a deviation of 0.004" and a 16" distance between the bearings (just guessing), worst case, the angle between the shaft and the axis could be off by plus or minus (2¡Á0.004/16)¡Á(60¡Á180/pi)=1.7'.? ?After a 180 degree rotation the polar alignment would be off by 3.6' if it were 0 at the CWD position.? So much for the arc second accuracy of polar alignment.? Frankly I doubt if it were that much.
The number of 2' is normal for my AVX.? If I rotate it manually 15 seconds east then 15 seconds west while taking a 30 second image at 6400 ISO using a DSLR with the scope's RA center of rotation in the FOV, I see 2 star trail circles on the LCD with centers that are about 2' apart.? That's because the manual rotation positions the axis in different directions going one way vs the other because of friction.? I have not tried this with my G11S yet but that would be a simple test to measure the effect of the gaps between the shaft and the needle bearings.
If the scope were perfectly balanced when tightening the clutches the touch points would be at the same side and the angle between the shaft and RA axis would be zero but the center would still be offset by 0.004" so the rong gear might still bind up unless using true SLWs or unless adding enough slack.
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76sec error on new OPW-11
I purchased the one piece worm from Losmandy hoping to get rid of some of my errors.
So far my 76 sec is worse than ever, and my PHD2 rms got worse.
I snugged the bolts for the worm block to worm housing first, then slightly snugged the bolts to the mount.
I then slightly loosened the worm block bolts to allow them to center with the worm, and then tightened them.
I've tried twice now and still get the same result
There's no noticeable backlash and it seems to run smooth, but obviously something is wrong.
The immediate thought is the worm blocks are "twisting" somehow and putting side load on the bearing.
Since I got almost the same results after R&R the assembly I wonder if the housing was drilled/bored off center.
Appreciate any help and input.
Thanks
Jim P
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Re: Losmandy GM-8: Anomalous wearing of R.A. shaft
The spring washer should be able to be smoothed easily. You will need them to be able to moderate the clutch pressure.? As others have noted with the RA shaft since there must be some clearance there is a high pressure side on the bottom against the upper bearing and on the top against the lower bearing. Normal rotation is less than 180 degrees. The pattern you see makes sense based on the comments above.?? Good luck. Michael.
Michael,
the shaft and the round plate on its end are definitely aluminum. Its weight is inconsistent with
a different material i.e. stainless steel. The areas with wearing signs (discolored) are fairly smooth
under finger touch, no scoring anywhere, but nevertheless, following your suggestion, I checked the
thrust bearing and the two washers just before the clutch knob, and they are fine and smooth, BUT, the spring washers
of both axes have serious burrs internally and are potentially dangerous to touch, so that might
explain the markings in that area of the shaft, although this doesn't cause problems on the DEC axis.
Anyway I removed the two spring washers and was more generous with grease on the thrust bearings
and the result of this is that the grip now is better than before and the overall stiffness is higher.
Thank yo so much for your precious hints.
Sandro.
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Re: Losmandy GM-8: Anomalous wearing of R.A. shaft
Michael,
the shaft and the round plate on its end are definitely aluminum. Its weight is inconsistent with
a different material i.e. stainless steel. The areas with wearing signs (discolored) are fairly smooth
under finger touch, no scoring anywhere, but nevertheless, following your suggestion, I checked the
thrust bearing and the two washers just before the clutch knob, and they are fine and smooth, BUT, the spring washers
of both axes have serious burrs internally and are potentially dangerous to touch, so that might
explain the markings in that area of the shaft, although this doesn't cause problems on the DEC axis.
Anyway I removed the two spring washers and was more generous with grease on the thrust bearings
and the result of this is that the grip now is better than before and the overall stiffness is higher.
Thank yo so much for your precious hints.
Sandro.
|
Re: Relationship between needle bearing wobble and variable worm mesh and backlash
Even though I have never taken off the ring gear assembly (no reason to so far), I think I know what's going on here. The problem is that the ring gear assembly is not sufficiently radially constrained by the "bushing" that it spins on. Further, the needle bearings that support the saddle shaft can't have a zero-clearance fit because you have to be able to pull the shaft out.? Thus there will always be slop no matter what.? Because of the slop in the needle bearings, the saddle shaft rests on the "lower" side of the bearing.? The first time you tighten the clutch (for example, in the CWD position) the upper half of the clutch mechanism grabs the lower half of the clutch (ring gear mechanism) offset and below axis.? If there is also too much slop in the central bushing, then this will cause the "ring gear eccentricity" when the axis rotates, because the axle always rests on the lower side of the needle bearings. In the older style Losmandy mounts, the worm assembly is on the lower side of the axis.? On the newer version it is on the upper side.? Thus, on the older style, when you spin the axis 180 degrees (or any amount) then this eccentricity "jams" the ring gear into the worm mechanism, tightening the mesh.? On the newer style, this moves the ring gear away from the worm, loosening the mesh. As I reported for the new G11 DEC axis, it still "works fine" with a too-loose worm mesh, as long as the axis is a little unbalanced to keep the worm teeth meshed on one side always. In any case, I always do a test of worm mesh before a long imaging run anyways, so this isn't a big issue for me. Here's a few possible solutions I thought of:
- Loosen and tighten the clutch before a prolonged session, and this should "reset" the ring gear eccentricity to what you set the original mesh to
- Find a way to better radially constrain the ring gear mechanism, for example a radial bearing instead of that bushing.? In this case, you can have a zero-clearance fit since you don't constantly need to pull this part off
- Modify the clutch mechanism to only give torque clamping, but minimal lateral clamping, so that the two halves can slightly slide relative to each other.? (Like an oldham coupling, hurr hurr)? For example, cut away most of the center section of the clutch disk but leave the outer ring.? Or just use a lighter clutch pressure
- Come up with a mechanism that forces the saddle spindle to ride on the ring gear mechanism instead of the upper needle bearing.? For example, a piece of tape or thin sheet metal such that when you insert the saddle shaft, it fits snugly in the bore of the ring gear mechanism.? This isn't a great solution because now the ring gear bushing supports the weight of the axle.
?
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
Michael B.,
??
That is interesting about using half the ring gear. When did a total tear down, clean and relube last year I did not mark orientation of either the RA or the Dec gears. So the new orientation for RA could have been any combination of worn in teeth and fresh teeth, depending on how it was put back together. I would think this could effect guiding depending where you are on the ring then, and could result in a change moving from one region to the other. I thought I had read in the forum the rings gears were aluminum alloy, with some type of hardening process used on the teeth. My brass worm gear had a noticeable depression in the center where the ring always rides. For a consistent rebuild, the user should mark and pick one side of the ring or the opposite, but I would think the used side would be more broken in and smoother with all the rough spots worm down a bit.?
Regards,
John
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
On Sun, Aug 1, 2021 at 03:45 AM, Michael Ben-Yehuda wrote:
Under normal operation if the clutch is never released and the relationship between the worm gear and CWD is maintained all the wear on the worm gear occurs on only one side over some portion less than 180 degrees. Over time the condition you report of a 'tight worm' at 180 degrees from CWD? is expected. Normally I would expect no wear on the ring gear anywhere around 180 degrees from what is normally your CWD position. Long period PE and PEC is impacted by absolute ring gear position because of the impact on worm mesh. This is somewhat mitigated by spring loading the worm so it can float in and out to maintain mesh and consistent worm/worm gear pressure.? ?Any shift in the DEC axis relationship to the worm gear by relaxation of the RA clutch will throw off your PEC because the absolute position of the worm gear has changed. Even with spring loading, there will be slight differences.
The problem with the clutched design is that there is no index of the DEC axis (CWD) to the RA ring gear absolute position. .? This destroys the 'sync' for guiding, PEC and backlash along with your worm mesh adjustment.
So, how can we set a consistent 'start position' for the mount that maintains the relationship???
I suggest the following:
Scribe the worm gear along it's top surface where it can be seen with the worm cover off. For some worm gear types where the cover cannot be removed a notched window may need to created to see this mark. The mark needs to be able to be matched to a specific mark on the mount housing at perhaps an existing landmark on he housing (window edge?) .?
Creae an index mark to match the DEC axis position to a known orientation to the mount RA housing. You might need to attach and extend a pointer.??
Although less critical for DEC, a similar situation exists because of the relationship between worm mesh and backlash.?
A similar solution can be applied.
Michael, Thanks for your comments. Let me comment of a few of the points you raise. "Under normal operation if the clutch is never released and the relationship between the worm gear and CWD is maintained all the wear on the worm gear occurs on only one side over some portion less than 180 degrees." If you use SharpCap to polar align your scope you will be loosening off the Ra clutch. I've never seen wear on the ring gear. The G11 ring gear if steel. The worm is brass and this is where the wear will occur. The Dec and Ra axes are different animals. To image objects in the Milkyway like the Lagoon Nebula you will need to rotate the Dec a full 180 degrees in both directions, so it's not like you can used just a portion of the Dec ring gear unless during Galaxy season perhaps.? "Over time the condition you report of a 'tight worm' at 180 degrees from CWD is expected " I assume you are making this statement because you expect wear to occur.? Lets assume wear is negligible for a moment. The fact that the Dec shaft can not sit perfectly centered on it's axis because of the needle bearing slop due exacerbated by the weight of the scope. When the clutch is tightened and you rotate the full 180 degrees it is unable to adjust it's position, hence pressure is placed on the ring gear that forces it into the worm at the 180 degree position. Of coarse as one rotates from CDW position this force steadily increases with the degree of rotation. If there was no movement between the shaft and the needle bearings then this problem would not exist.? "Long period PE and PEC is impacted by absolute ring gear position because of the impact on worm mesh." Agree. "This is somewhat mitigated by spring loading the worm so it can float in and out to maintain mesh and consistent worm/worm gear pressure. " My Ra is spring loaded and I hope that this is the case. Dec is a different animal because backlash impacts guiding. I recommended not spring loading.? "Any shift in the DEC axis relationship to the worm gear by relaxation of the RA clutch will throw off your PEC because the absolute position of the worm gear has changed. Even with spring loading, there will be slight differences." True. As for your idea of indexing the worm position, I feel this might be quite difficult to implement, however I'm fortunate in that my Dec worm is fully visible based on the mods I've made.? Really the right fix is to sort out the needle bearing ID shaft fit problem. I have some ideas on how this might be done and will if successful post a video. It hinges on getting the correct press fit which these bearings do not currently have. Best, Peter
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Re: New subscription to Losmandy user group
Welcome Frank! glad to have you aboard
Brian
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Re: New subscription to Losmandy user group
Thanks all!,
Just spoke with Losmandy yesterday. Seems there are some issues with LW tripod parts holding up some orders. Figures...? ?Looking forward to the new mount.? There is penty of good support for it.? Now if I can just get my hands on it. :)
BR,
Frank
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Re: What result I can get with the current OPW in my old G11?
When you replace the worms you might want to consider running the worm gear 180 degrees to CWU position, then releasing the clutch and moving your Dec axis back to CWD.?
This puts you in the "unworn" side of the worm gear when installing the new precision worm and OPW.? Might as well use the "new side" of the worm gear with the new worm. Over time if you've run motors with the clutch free, there isn't really a completely new worm gear side, but it will still have much less wear.?
Similar action can be taken for DEC.?
?
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
Under normal operation if the clutch is never released and the relationship between the worm gear and CWD is maintained all the wear on the worm gear occurs on only one side over some portion less than 180 degrees. Over time the condition you report of a 'tight worm' at 180 degrees from CWD? is expected. Normally I would expect no wear on the ring gear anywhere around 180 degrees from what is normally your CWD position. Long period PE and PEC is impacted by absolute ring gear position because of the impact on worm mesh. This is somewhat mitigated by spring loading the worm so it can float in and out to maintain mesh and consistent worm/worm gear pressure.? ?Any shift in the DEC axis relationship to the worm gear by relaxation of the RA clutch will throw off your PEC because the absolute position of the worm gear has changed. Even with spring loading, there will be slight differences.
The problem with the clutched design is that there is no index of the DEC axis (CWD) to the RA ring gear absolute position. .? This destroys the 'sync' for guiding, PEC and backlash along with your worm mesh adjustment.
So, how can we set a consistent 'start position' for the mount that maintains the relationship???
I suggest the following:
Scribe the worm gear along it's top surface where it can be seen with the worm cover off. For some worm gear types where the cover cannot be removed a notched window may need to created to see this mark. The mark needs to be able to be matched to a specific mark on the mount housing at perhaps an existing landmark on he housing (window edge?) .?
Creae an index mark to match the DEC axis position to a known orientation to the mount RA housing. You might need to attach and extend a pointer.??
Although less critical for DEC, a similar situation exists because of the relationship between worm mesh and backlash.?
A similar solution can be applied.
Michael
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Re: Losmandy GM-8: Anomalous wearing of R.A. shaft
It can be that the RA axis shaft has just lapped in to true roundness. I notice that some of this is in the area of the thrust bearing as well. Is it smooth or is it scored??
I'd only be concerned if it feels like there is scoring. Check the thrust bearings Inside diameter surfaces. to make sure they are smooth and the shaft is lubricated where those bearings are.?
Some of the tolerances are very tight.? I've noticed some similar discoloration on my G11 RA axis shaft and my mount is a bit newer but still Gemini 1 era.? It's good to to service those bearings as lubricants age
and if it hasn't been done in 11 years it's overdue. Since the clutch friction plate was contaminated, obviously there has been lubricant migration.? There are some recent threads on bearing replacement and PE improvement that you might want to review since you are servicing the mount.?
Good luck,
Michael
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Re: Losmandy GM-8: Anomalous wearing of R.A. shaft
Michael, thank you for the helpful tips and for indicating the source of possibly better replacement parts in Europe.
Sandro
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Re: Losmandy GM-8: Anomalous wearing of R.A. shaft
Sandro,
No idea exactly what caused your steel shaft discoloration, but it cannot be anodization.? The shaft is steel. It may have been hardened and appears darker color.? It seems simply polished where weight on would have been applied on one side of the top and the torque would have been applied on the opposite side of the bottom.??
The needle bearings are prone to "gumming up" meaning that the roller needles become stuck from oxidation or dried lubrication.? Try soaking the bearings by spraying in a light oil like WD-40. If the needles will roll freely then they are ok.?
Yes the plastic clutch disks can slip if they become oily.? Cleaning the clutch surfaces helps get their grip back...for awhile.? It is better to replace the slippery clutch disks with a higher friction? clutch material that will prevent slippage and not allow oils on to the disk surfaces.? I supply those disks domestically to US customers.? David Partridge can supply European owners.? ? Shipping to other destinations is costly and error-prone.??
Best of luck, Michael
Hello everybody,
I have a GM-8 that I purchased new in 2000, which I have not used heavily;
so it is still quite new and behaving. Lately I noticed that the clutches
tended to slip, probably due to grease leakage to the nylon discs.?
So I decided to disassemble the mount
to perform a complete cleaning and regreasing. I started with the DEC axis
and everything was fine and OK. When I disassembled the R.A. axis I found that
the shaft shows signs of irregular wearing in correspondance of the upper
and lower needle barrels, on opposite sides of the shaft
(see video ). Only the
anodization seems to have come off and there are no signs of serious grinding.
Nevertheless, prior to disassembling, the axis rotated quite smoothly and
apparently there was no play whatsoever.
Does anybody have an explanation for what has happened and how to prevent
possible further damages?
Thank you all.
Sandro Barbanera
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Re: Losmandy GM-8: Anomalous wearing of R.A. shaft
Sandro,
It is surprising that anodizing was used on a moving part, as wear would eventually remove the coating over time. In present day mounts, I think these shafts are all stainless steel. The patterns you see can be explained by the way the shaft rides inside the bearings, as Peter has stated, with some slight gap between upper and lower bearings. But if you are not seeing any problems with shaft rotation and you don't have any issues with problematic periodic errors, you are probably OK.? ?
The clutch discs can be replaced as the nylon wears down over time. But after cleaning you might try sanding them down with some 220 mesh sandpaper to roughen the surface a little. But after 20 years you may wish to get some new ones. Thoroughly cleaning where the discs ride with some solvent should also help a bit.
Best regards,
John
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Re: Losmandy GM-8: Anomalous wearing of R.A. shaft
If this is the link I don't think there's much to be worried about.
Can you feel a deformation with your fingers?
------------------------
Jim W
Phoenix, AZ. USA
Losmandy GM811G, NINA 1.11, ASI2600MC Pro, Sky-Watcher Scopes
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Re: Losmandy GM-8: Anomalous wearing of R.A. shaft
John,
yes, I posted a new message, this time with a link to youtube.
Thank you.
Sandro
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Michael Herman