On Sun, Jul 11, 2021 at 10:58 PM, John Kmetz wrote:

This information is pretty interesting, Peter. If you have some pics of the mount with the bearings removed would love to see them. In fact, there should be a file section here for mount disassembly instructions and pictures if there is not one already. May I ask how old your mount is? Also wondering if Steve Losmandy has changed the bearing seats or manufacturing tolerances over the years. If he was responding to the forum 20 years ago, he may just adapted manufacturing techniques as a response. My shafts rock a bit more when the axis locks are loose, and less when they are tightened. After locking down, I assumed the remaining play would be from the worm rocking back and forth a bit inside the bearing blocks, but you may be indicating the needle bearings are playing a role too.

As a sidebar, I was checking online last night about possible techniques for worm polishing to improve surface profile. There seems to be two techniques available. One using the original machining equipment that made the gear, and replacing the cutting head with a polishing head which retraces and smooths down the surface profile. The second is placing the finished gear in a vibrating container of polishing media, such as ceramic shapes or even walnut shell fines. One company oft refereed to is REM:



It would be nice to see if they would do a single worm or a small batch of worms. Then we would have to check the guiding achieved by the unpolished vs. polished piece. A nice experiment for someone who has the time and inclination :).

Regards,

JohnJogn,

John,?

I've spent countless hours trying to remove my Dec backlash. I have to assume there is the same problem in Ra, but masked by the fact that it is continuously moving, but would affect GOTOs. Here is my perception on the sources of backlash:

1. Worm-gear mesh. I resorted to applying a lot of pressure between worm and the gear. This is possible with the right grease. If too much force is used the Dec motor will likely stall as we all know, so it has to be backed off with the adjustment screw, thus introducing backlash so I plan to lap my worm. More on that later.?
2. Worm rocking back and forth between the bearing blocks. The worm ought not to move if the bearings are loaded with a bevel washer and screwed down. You can see any move easily enough with the cover plate removed if using the original worm block (not the OPW).
3. Gearbox. There is play in the bronze bushings of the output gear. It moves back and forth a little, but I do not think it plays a role since the worm blocks are locked into position. This is not however true is using the spring loaded OPW. I no longer spring load the Dec axis.?
4. Needle roller bearings. This is the possible elephant in room. Without being too negative hear, the Losmandy mount was originally designed for visual were a little play was OK if one could achieve 2-3 arc-sec of accuracy. Not true for astrophotography for long focal length setups. There was a design decision made to use inexpensive 3/4" long Torrington full compliment bearings (1" and 1.25 long bearings are available as are high precision bearings that have a larger OD). It's not clear what the tolerances are for these Torrington bearings as I could not find any values for the ID. This is not a good sign.? There is also the diameter of the shaft (1.25 +/-) to consider and whether there is wear on older mounts like mine. I believe Scot himself said that this was an issue (see conversation in the link I posted). If I'm not mistaken here recommended adding a third bearing to help with this problem (especially for Dec where the distance between the bearings is large), but indicated that in some cases it might be difficult to get the shaft through the bearings because each end is machined independently, so I assume there could be an offset. This is also perhaps why he went with 3/4" and not 1.25" long bearings. Clearly, a tight fit would make production more difficult so we have two interests working against each other each. Cost to manufacture (fitting and cost of bearings used) verses high precision.
5. The Oldham coupler. The only solution if this proves to be the problem will be to use a rigid one-piece coupler.

Lapping One's Worm and Gear Wheel

There is a excellent article on polishing the worm and gear wheel in combination here:??Sadly the images are gone. I plan to do this using higher rotational speeds and series of powders (Step 1. 1200 micro fine Aluminum Oxide, Step2. 3.5um Red Cerium Oxide - 3000 grit. Step 3. 2um White Cerium Oxide - 6000 grit.?

Buffing One's Worm

I have quite the collection of worms so I will buff one to see what results I get. I intend to do this by holding one end with a bearing while spinning with a drill against the buffing wheel. I'm going to use a fine compound like jewelers rouge.

Peter

Yes, the shaft rattles, but that only has the saddle attached to it.? This does not affect the worm and ring gear engagement since that is set by a separate set of bearings that do not wriggle.? Thus it will not affect backlash.
I briefly looked for a 1.25" ID 2" OD bearing (which would constrain the shaft relative to the black anodized body), but could not find one.? That's weird, since I know of several metric bearings (on bicycles) that are of even thinner profile.
In any case, you can't preload / adjust a needle bearing radially, so it hardly solves the problem.
Also, even though this joint CAN rattle, in practice it doesn't because the pre-loaded thrust needle bearing (at the clutch knob) constrain radial movements against small forces.
I don't care about pointing accuracy since I have never even bothered to align my telescope's dovetail with the optical axis.? I use plate solving anyway, so no big deal.

This information is pretty interesting, Peter. If you have some pics of the mount with the bearings removed would love to see them. In fact, there should be a file section here for mount disassembly instructions and pictures if there is not one already. May I ask how old your mount is? Also wondering if Steve Losmandy has changed the bearing seats or manufacturing tolerances over the years. If he was responding to the forum 20 years ago, he may just adapted manufacturing techniques as a response. My shafts rock a bit more when the axis locks are loose, and less when they are tightened. After locking down, I assumed the remaining play would be from the worm rocking back and forth a bit inside the bearing blocks, but you may be indicating the needle bearings are playing a role too.

As a sidebar, I was checking online last night about possible techniques for worm polishing to improve surface profile. There seems to be two techniques available. One using the original machining equipment that made the gear, and replacing the cutting head with a polishing head which retraces and smooths down the surface profile. The second is placing the finished gear in a vibrating container of polishing media, such as ceramic shapes or even walnut shell fines. One company oft refereed to is REM:



It would be nice to see if they would do a single worm or a small batch of worms. Then we would have to check the guiding achieved by the unpolished vs. polished piece. A nice experiment for someone who has the time and inclination :).

Regards,

John




?

Chip,

> Surely the bearing blocks are sitting flush on the deck plate and not as is shown in the photos way up off the base deck!?
Yes, of course. I figured showing a picture of bearing blocks in their normal position was unnecessarily pedantic - so I repeated the text from my first post for how to tighten down the blocks snug/off snug after simply using soft finger pressure to push the blocks straight down into their holes.?

Based on your input to this forum, I respect your experience. Do you think this idea has potential issues/risk? I was concerned - but it seems to be working as expected. Worst case, I figure I could just tighten down the blocks as I would normally after having adjusted them (e.g. feeler gauges or intuitive sense of motor duty loads / sound).

Greg

I was asked to start up a sperate thread on this subject, which I think is a good idea as this is a significant issue for some. After making numerous mods, I now realize I should have looked at this first. If buying a used mount I would recommend starting here with any tune-up.

Whether or not wobble in Dec, RA or both axes is a significant problem is to be determined, but I suspect it is. Most certainly it must effect backlash and most likely the ability to carry heavier loads and maintain excellent guiding performance.?

In doing some research I came across this posting from 2000.?/g/Losmandy_users/topic/g11_fix_source_for/21183709?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,1,40,21183709

I just took apart my Dec axis and was shock by the degree of play. This is? also true of the Ra axis but not quite as bad. So what to do? In the note by Neal Barry from 2 decades ago be suggests adding a third needle bearing and shimming the shaft. There is room for a third bearing in both Dec and Ra.??

In researching bearings there seem to be two designs:?full complement drawn cup and caged drawn cup.? ?

Torrington bearings used by Losmandy are the original full compliment design. I've opted to use the more expensive caged design. There advantage is the rollers stay axially aligned. This is what I ordered:?

How hard is it to removed the old bearings?

Not hard at all. On my G11 there is a brass inset end on the housing. The bearing opposite the bass end I tapped out using a piece of 1/2" dowel catching the metal edge. It came out very easily. The brass end was more difficult because less of the edge shows, so a whittled down a piece of 1.5" dowel bought at Lowes. The overall diameter was reduced a bit, a small flat was added, and the business end I reduced the diameter further. I did this on a belt sander, but one could use an orbital sander, it will just take longer.?

How hard is it to insert the bearings?

Again this was much easier than I thought it would be. I was able to press in the bearing with my hand. The new ones might be more difficult. Nevertheless, they can be tapped back in using a block of wood. On the brass end the 1.5" dowel would be used to seat it in place.?

How much play is there?

In my case a lot. The shaft appears to be in spec. 1.25 - 0.05. I will not know if the bearings are the source of the problem until the new ones arrive. If the bearing is tight to the shaft job done. If not then I will shim. I bought this material just in case.??To test the effect of shimming I used tin foil and it worked great.

What result am I hoping for?

Significantly reduced backlash, better guiding especially in Dec. My current Dec backlash is around 2500ms. With all the mods I've made I have singerly failed to reduce it thus far. Keeping fingers crossed.


Here is a quote from Neal Barry from the above thread.

Lol I’m glad it worked. I discovered the problem by following the scientific method: put it in my pocket during boot up and got it misconfigured by mistake :D

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On Sun, Jul 11, 2021 at 10:36 AM, David Malanick wrote:

Can you use an OAG?
Going from Orion ST80 with the Orion Star Shooter Auto Guider Camera to a QHY-M OAG and ASI174mm camera was a game changer for me.? Now multi-star guiding with 12 stars selected.

I’d love to but I ha e a DSLR and I don’t think that’s possible

my plan is get the 290 and use it with same guide scope. Then this will transfer over to a good OAG camera once I upgrade to an astro cam

im happy with my RMS numbers because 0.8 is basically 0.1 pixel and anything less than that I don’t trust.?

it’s the spikes which are now sometimes hitting 3” and the non-round stars in the corners (almost certainly not related to the mount ). Sometimes I see them quite prominently and sometimes barely at all.?

Programming a PEC curve might help but I’m not going to tackle that just yet.?

Can you use an OAG?
Going from Orion ST80 with the Orion Star Shooter Auto Guider Camera to a QHY-M OAG and ASI174mm camera was a game changer for me.? Now multi-star guiding with 12 stars selected.

I have just carefully adjusted both my DEC and RA worms using finger pressure to squash the two ends together and feeler gauges to adjust the gap between the body and the non-motor adjustment block.

Adjustment is very critical 0.002" makes the difference between getting a MOTOR STALLED message and no backlash.? I am coming to dislike the motor / gearbox / worm setup on this mount quite a bit.? I really dislike screwing the motors into the plastic gearbox plates.? They wobble and I am always scared that I'll strip the plastic thread.

My mount has steel worms which seem to work well enough but I cannot do any PE measurement right now for a number of reasons.? I fear that I may have to spring for at least one new OPW and brass worm later this year.? Along with a Gemini 2 upgrade this is getting to be an expensive mount even though I got it cheap.? Honestly, iOptron is beckoning me.

On Sun, Jul 11, 2021 at 02:56 AM, alan137 wrote:

On Sat, Jul 10, 2021 at 12:56 PM, Nick Ambrose wrote:

1. Guide assistant said my backlash was 3500 ms so it did not recommend turning it on. It recommended guiding in one direction which did not work well. Brian V said that PHD cannot accurately measure BL on the spring-loaded worms, so not to enable the comp

I have a very long post describing the DEC axis backlash
/g/Losmandy_users/message/71205

Thanks! I am going to check this out.
Unless DEC affects the RA, then it is less of a concern right now, although might need some attention
When I imaged at DEC=60, RA was insanely good. Last night was DEC=30 and definitely a few excursions

The RA spikes still persisted and I did everything in software I could think of to tweak them, and nothing really had an effect.
Guiding was closer to 0.8-0.9 (DEC=30 not 60). Still OK but for the spikes

Things I can think of?

1. My guider scale is just not good enough and I need (at some point) to upgrade. Definitely possible
2. PHD2 "bug" -> could be just some weird thing. Who knows (somewhat unlikely ?)
3. I did change the weight, moving it further East. Its a 7 pound weight so I thought it would generally be OK to move.
I put it close to the end of the CW bar, and PHD2 kept complaining it could not move the star enough so maybe this has more impact than I thought ?
Maybe check balance again
4. Related to #3 - maybe it's possible Gemini is not getting enough power (since it couldnt move the axis with the weight moved)
I have an 18V power supply but maybe there is some issue here ? (It steps up from 12V)
5. Wires - Next time I will tweak my wires. I think they are tight, but if I try to re-route them and things change, then I will at least have something to look at

Other than that, I guess I don't have much to do except ignore them and assume my images are not affected.
I'm processing one from last night right now, so we will see

It doesn't feel satisfactory but at this point I dont want to tinker, and definitely don't want to void any warranty

I know these things are tough to debug but it doesn't feel super satisfying honestly

Upgrading the guider is definitely a "good thing" though. I think I can easily get an ASI290 and drop it into the current scope, which will help somewhat
Then later I could look into a better scope - but that's going to need a lot better mounting hardware than I have

?Hi Greg,

Surely the bearing blocks are sitting flush on the deck plate and not as is shown in the photos way up off the base deck!?

--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astropheric Weather Forecast - South Pasadena, CA?

On Sat, Jul 10, 2021 at 12:56 PM, Nick Ambrose wrote:

1. Guide assistant said my backlash was 3500 ms so it did not recommend turning it on. It recommended guiding in one direction which did not work well. Brian V said that PHD cannot accurately measure BL on the spring-loaded worms, so not to enable the comp

I have a very long post describing the DEC axis backlash
/g/Losmandy_users/message/71205

Please start another thread to discuss this

Totally correct...first thing is re-calibrate the HC screen on boot.? Try this is first.

The fact got past into screens...means it appears to be working so maybe re-seat your HC microSD card.

Dos wiggling the cables cause it to stop?? Clean inspect the sockets and plug pins.

If its a G2 first you can plug it into serial 1 port (but first lower its Baud to 9600bps) and try that port.

It's possible the housing screws but my guess this would manifest in differing issues like slewing HC functions.

Yes it could be a HC or Main unit issue but probably not and no use thinking of this yet.

Lest see how this goes first before looking further
--
Brendan

Past replies on the forum have suggested that if the HC housing screws are too tight the touch screen may not not work properly. Try loosening and re-snugging be hand.?

Did you try re-calibrating the screen? Right before the boot options menu shows up you can press the screen to re-calibrate it.?

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I have new worms running in both axis. I have no expedience to know how things change as they wear or how long that takes. To what extent are the one PHD2 tracking spikes a function of the worm surface? Does tracking improve or get worse as they wear in? Since I have a few worn worms I thought I might lightly buff one while spinning in an electric drill. I have to assume a polished worm has less friction/stiction.?

Another question I have is what effect do the needle bears have on the system. Do they have a frequency profile? I do have some axis movement. My rig is rather old, and I suspect these have never been renewed. However, it looks like a difficult job, not to be taken on lightly.?

Peter

Peter,?

Not sure if there is a set period for break in, but over time all meshing parts start to wear and smooth down as they loose metal on the tops of the tiny asperities on the surfaces. If you have ever changed the oil in your car after the first 500 miles, you will see the fluid is full of shiny metal fines, shed from the moving parts inside the engine. Same with the worm and rings gears wearing and smoothing over time. Of the worms I have used, my original 3 year old RA worm works the best, and has a noticeable depression in the center where the ring gear has worn it down. How to pre-wear or polish down a new worm is a good question, but doing it evenly and properly would probably involve precise machinist equipment and micro-measurement instrumentation not many have at home. If you polish it unevenly even much less than a thousandth of an inch, you are probably creating new errors. Most I think would love to hear about this if you can achieve it.

The main needle bearings, from my disassemblies, look like they were hammered or pressed into the main mount frames at the factory with perhaps hydraulics or a special knock-in tool which would fit precisely over the bearing races. How to knock the old ones out and replace I have not ever considered yet. With proper lubrication they look like they would last decades, IMHO.

Best of luck,

John??