I was able to run further tests last night, but smoke moving into our area cut the session short.

I put back the 25:1 McLennan gearbox on the Ra drive and ran a guiding test with the 256 tick optical encoder. Slew rates are now fully restored. I also changed out the Ra thrust bearings to those sourced from McMaster. The net result saw a very significant reduction of 2600s error I previously identified and attributed to the top thrust bearing. As you can see from the attached PHD2 screen shot by guiding rms error was 0.28 arc-sec. Later in the evening I changed out the Ra motor encoder to 1024. I saw no real improved in Ra performance which leaves to with the following overall conclusions:

1. The stock Losmandy thrust bearings are a major source of problems. I attribute stiffness of rotation, worm misalignment, and significantly large 2600s error to them. My suggestion with anyone who buys an older or new mount is to change these to German made bearings sourced from McMaster.

2. The Dec axis greatly benefits from a smaller step size. This can be achieved by switching out the 256 tick encoder to a 1024 tick encoder. Cost is around $65 sourced from US digital. A smaller step size make sense as it leads to a more subtle control, and it most noticed when one's polar alignment is excellent.??

3. Replace the Oldham couplers with rigid couplers. This facilitates alignment of the motor to the worm. This mod it difficult to pull off as the couplers have to be made from two parts, previously listed. Cost is around $20 for both Dec and Ra. Since there are two pivot points that have to be aligned, it requires loosening of the coupler screws and gearbox mount screws and alignment the assembly while rotating the motor. When aligned correctly the motor will not bob up and down, Done right the native 240s error in Ra will be very much reduced and there will be no requirement to used PEC to achieved a 240s guided error of under 0.2 - 0.15 arc-sec.

4. Reduction of the 80s bearing error in the OPW remained stubbornly large. After repeated tests I found the best thing was to used a single Bevell washer arranged to put pressure on the ball race. In my case I reduced the 80s error to under 0.3 arc-sec.

5. Replace the Ra gearbox to the McLennan gearbox (not necessary for Dec) . I saw no real benefit to reducing the step size. This makes sense because the Ra worm is continuously rotating. The reason to replace the gearbox is to eliminate the large 32s error of the Losmandy gearbox.?

6. Spring load the Ra worm ( did not test the locked down cased), and add a 2 lb bias weight to load the worm on the east side. The keeps the worm permanently engaged on the right face of the worm gear both before and after a meridian flip.?

7. Use TVC correctly to eliminate Dec backlash. The ideal arrangement? is to have the worm mash on both sides to the ring gear, but not have the pressure be too great so as not to be able to turn with one's fingers. I found a spring loaded arrange in Dec to be detrimental to achieving a low backlash value. TVC is there to cancel out any backlash. The thrust bearings play a big role here because you want the ring gear to turn easily when the clutch is tightened. If using the 1024 tick encoder then TVC will be 4x larger in value than in the 256 tick encoder case (my setting is 45).?

That it folks! Happy imaging,

Pete

Michael,?

Mark Crossley identifies the issues I"m seeing quite accurately.
I think I'll go back to the thinner thrust bearing to reduce the significant exposure of the needle bearing assemblycaused by the extra thick bearing and?
instead look to putting spacers between the clutch collar and the Losmandy spacer. Moving the wavy spring to be between the clutch collar and the spacer provides more even?
pressure against the thrust bearing which will prevent warping.?

He identifies the Losmandy spacer ring being too narrow as the root cause (narrower than the DSC device it replaces). If that is true then this issue should be common to anyone with this generation G11 that has the polar scope installed. It either manifests as a polar scope that doesn't seat correctly or a clutch collar that feels tight because it's putting pressure on the polar scope not the thrust bearings. That can cause all kinds of issues with the RA axis performance.?

Just thinking out loud here, Michael, but I am wondering if the fresh application of the lubricant grease during a rebuild is not contributing a small amount to the separation of parts. When the lube is new and freshly in place you are creating a hydrodynamic film just from the viscosity of the fluid (grease) over which the parts can ride. Over time the viscosity can break down a bit and and also it gets pushed aside into the surrounding voids as pressure is exerted down on the moving surfaces. Whether the film integrity amounts to the size of the distances you are factoring here I don't know. A measurement would need to be done right after assembly, and repeated after some use period. After displacement of the grease you are left with an ultra thin film and relying more on the chemical nature of the additives over the original lubricant film volume. Or measuring the entire assembly clean and dry versus lube over the the working parts might show this difference. Maybe.

Thanks for the tip Michael.?

I will certainly check out Mark's site.? There is a copper wavy spring under the PS flange. With the thicker thrust bearing there is now enough space for the polar scope to seat correctly.?

I agree that doing the alignment with software tools and an imaging camera makes life easier. The other EQ mounts I have don't have a polar scope at all.? I discovered the problem in the way the clutch was behaving. When the polar scope hit, the clutch collar would feel tight even though it wasn't tight against the bearing. It could have easily damaged the polar scope.?

@Brian V.?

My apology for any inference about Losmandy in this.? As I go through the mount I'm finding more and more oddities that are obviously the previous owner's doing.?

If it was serviced in 2019 it's clear to me now that things were done since then, and none of it for the better.?

I'm was hoping to be able to just do the easy routine of? cleaning clutch plates and partial lubrication. It's better for sure, but I also feel that there's more improvement
to be had.? I'll probably just plan on a full "super tune" type tear down. Mounts like this deserve the effort.?

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The vibration settle down from moving the axis may be coming from a different place than when you touch the focus. Perhaps there's some oscillation in the axis that might be reduced with a bit of increased force on the clutch. That clutch sets the load on both thrust bearings.

?

I tried swapping the worm gear without much luck. Should I try to swap worm?

Here is a graph without guiding and frequency analysis from PHDLogAnalyzer

I have an old GM8 and I am not able to get decent guiding with it.
Maybe I am pushing it too much - I have a GSO RC8, which is about #25.
I am getting about 1.5" RMS, which produces egg-shaped stars.
I am using OnStep controller with 4:1 belt drive.
Attached is guiding graph.
Any ideas on what can be improved?
I have the mount east heavy.

? ? ?Hello Sean,?

Welcome Frank,
A? wealth of knowledge and very experienced users here.? I've found it very helpful.

Just bought a used G11 recently which is my 1st Losmandy mount which I'm still tuning up and getting parts
together for.? The usual cloudy nights anytime something new arrives, so it's all working out.? ?:)

?

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Hi Sean,

Welcome to the group. I am new to Losmandy as well. I just bought a used G11 mount and am reading and learning a LOT from this group.

There are a lot of very experienced people here. A real wealth of knowledge and lots of help and support.?

+1 what others have said
TKS? if you are going to be?setting up and taking down the mount each night.?

AKS if you intend to travel to multiple locations to do your observing.?

Sort out the power supply and power cables you'll need.

Totally agree with eliminating the need for small tools and wrenches wherever possible.

I might suggest you add to the list a couple small strap wrench.(Photographers may call them 'filter wrenches'). or flat rubber bungee for that purpose.

With machined tolerances tighter than what's typically seen it's possible that threaded parts can get 'stuck' from the small bits of debris especially if they get over tightened.? My mount is more than 10 years old and the fastener fit is still noticeably closer then other gear I have.?

Nice thing about a mount that is all machined is that you don't need to crank down?on the fasteners to have things stay put. In general, snug tight is just right.? I don't know what other
mounts you may have worked with, but for me it's so nice to no longer feel non-true castings flex as you torque a hex bolt realizing that whatever was set is now off. It's still advised to work with things 'snug' and then slowly tighten when doing alignment, but what a difference.
For me anyway it's really a pleasure even when dealing with a used mount and needing to fix up bits of accumulated maintenance and previous wrongdoings. It keeps me busy while waiting for a night that's not cloudy or foggy LOL.

Clear skies,

Michael

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Welcome to the group Frank!

This is a great group to find information and assistance when needed.? Feel free to ask questions when you get stumped.? Everyone here is helpful, knowledgeable, and persistent in finding solutions.

- Jerry?

Ken,

You might want to try looking at the males and female threads using a magnifying lens, and use a flashlight to look inside. See if there are any burrs getting in the way. Sounds like it was a tight fit from the start, and you plowed up the high spots. You probably won't get the right insertion until the obstacles are out of the way. Other than what's been recommended already, you may want to contact Losmandy support since you are under warrantee.?

Good luck!

Hi Frank,

Congrats on your mount purchase! You'll find lots of info searching through this forum and also on the Losmandy YouTube channel. Good luck with your setup!

John

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On Mon, Jul 26, 2021 at 12:34 PM, Michael Herman wrote:

If truly only 2 months old, contact the factory and ask for a replacement counterweight rod with threads slightly reduced in OD.? Stop putting time into this...it was not made right.? The correctly made shafts and bore holes go into each other with hand tightening.??

IF it worked originally the first two months, there's nothing wrong with the thread size.

Thanks for all the thoughtful replies.

I did clean out the female threads with some nitro-solvent (gun bore cleaner), then lubed with a light coating of gun oil.?

No change as yet. I see from the comments I want to more closely inspect the threads, and try some additional cleanings, and perhaps some of the other steps mentioned.?

Thankfully it is still functional, goes deep enough that it is in safely/solidly.? I'm going to take my time trying a few of your suggestions first. Since I got the mount less than 2 months ago, I'm still too excited to use it/learn it to consider sending it in for service!

Thanks to all,? I can see this is a great community and I look forward to participating in it!

On Mon, Jul 26, 2021 at 05:49 AM, alan137 wrote:

Then again, I am using a BIG 12" F4 tube newtonian.?

Allan,

I'm excited to see that you can carry the bad boy!.??I think I might mount mine to the coming weeks.?

Do you have plans to upgrade the optical encoder to 1024. I think you will see a very noticeable benefit. It's a $65 investment and you do not have to remove anything from the drive other than the motor end plate can do everything insitu.? It would be nice to have a second reference point to go by. With a minimum step size of 0.56 arc-sec and I would imagine longer settling times due to the weight, having the ability to make smaller 0.14 arc-sec steps would be beneficial. I've ended up with a min step size of 0.05 in PHD2, compared to 0.4 before I made the alteration. With good polar alignment I would expect on only having to make little tweaks.?

Here is my guide graph from last night showing just how small the corrections are and lack of reactionary overshoots. The scale is +/- 1s if the scale is not readable

?

I found it useful to remove the motor and use my fingers to judge the worm mesh to get both side touching. It's such a fine adjustment thing. Also, I would highly recommend changing out the thrust bearing. It made a large difference for me.

Peter