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Adjusting out gear slop.

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#1 av8or

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Posted 22 May 2013 - 12:06 AM

Hi guys, having a minorish issue here with my CGEM DX mount. It's about a year old and ever since I got it, there has been a few issues with it. I took care of most of them excluding gear slop. It is apparent in both RA and DEC, visible when you try to move it with your hands and extremely apparent when viewing through the scope. After a bunch of reading, I dove in adjusting the gear mesh for RA and DEC. I thought I had got them perfect but decided to run both axes through their extreme limits. This is when I noticed that about 90 degrees form my original position in DEC, I was binding. Then 180 degrees from that position, I had slop. Also, It wasn't a gradual slope from binding on one side to slop on the other, it varied a few times. The RA axis has a similar issue but not as severe. For now, I've adjusted the mesh at what was a binding point so it no longer binds in any spot. The down side is that I have a decent amount of slop again in certain areas. Just wondering if anyone is having a similar issue.

Been thinking about doing a hyper tune since there are "stiff" points in both axes when rotating manually with the clutches disengaged. Not a huge deal but it makes it difficult to balance the mount. I'll be more serious about this option if anyone thinks this would help my slop issue.

Thanks for any and all input.

#2 MHamburg

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Posted 22 May 2013 - 07:37 AM

I had similar issues, but they were all resolved with Ed Thomas' hypertune. I heartily recommend it!
Michael

#3 John Carruthers

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Posted 22 May 2013 - 08:34 AM

not uncommon to have high and low points on a mass produced wormwheel. The cure is to index the worm to the wheel, then lap the worm/wheel with lapping oil, strip, clean and reassemble.
If you do go this route don't be tempted to use anything other than lapping oil. I have seen horror shows where people have used T cut, valve paste, toothpaste etc.
For a steel & brass gear set I leave it running with a slow drill for a day or two (not too tight mesh) then clean it up. Usually all the high points are eliminated.
Also check for worm end float.

#4 av8or

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Posted 22 May 2013 - 09:06 AM

I've never hear of lapping a wormwheel before. I'm guessing the lapping oil is slightly abrasive and essentially grinds out all of the high spots as you run the set for a day or two? Sounds like a great idea!! When you say to index the worm to the wheel, what exactly do you mean? Also what is worm end float, lateral slop? If I use this process, can I take the whole wormwheel assembly off of the mount or must I apply the lapping oil to the gears and leave it on the mount. And I think if I have the whole thing disassembled I may as well do the hypertune.

#5 neilson

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Posted 22 May 2013 - 09:49 AM

Hi,
Its normal to have a high spot and a low spot on the worm wheel. You adjust the lash on the high spot. Having a small amount of play on the rest of the wheel is normal. This is why you set the balance slightly heavy on the south and east. This will keep the worm engaged while tracking. Lapping the worm wheel can be done to reduce or remove the high spot but this should be done with care.

neilson

#6 av8or

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Posted 22 May 2013 - 08:59 PM

Update; So I ended up emailing Ed Thomas from Deep Space Products asking if he has dealt with the issue during the hypertune process. He recommends to forgo the lapping procedure. He mentioned that it must be done in place. I'm not sure if that is because there is no way to actually take out both gears completely, or there is just no easy way to remount the gears after taking them out. I sent a reply asking what he thought about designing and building a fixture at the shop I work at specifically for lapping my gears. Currently waiting for a reply. He also mentioned that over tightening the clutches can deform the ring gear enough to cause backlash and setting the gear mesh is best done with the clutches released. Regardless of all the lapping talk, I've decided to do the hypertune during the next full moon and I'm really looking forward to doing that and having a better performing mount!!
Thanks to everyone so far.

#7 wolfman_4_ever

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Posted 22 May 2013 - 10:05 PM

Been down this road before.

The worms are spring loaded. if there is a high side, which you have, the spring should spring away..

I have also found that the worm housing (motor/worm/spur gears)can adjust latterly where the housing bolts to the mount. On the pro this is the three 5mm alan bolts on the bottom. you can loosen these bolts and the housing can slide forwards and backwards on the wheel about 2mm. This adjustment allows you to line up the wheel and the worm straight. I have found this adjustment to be the major cause of large PE, resonance in the way the worm and wheel interact, etc. If this is not straight, the brass wheel could slowly grind away at your worm at certain angles.

Also, you could have a high spot where the 2 spur gears mesh. the 180 high side could be on the large spur gear that is connected to the worm.

#8 EFT

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Posted 23 May 2013 - 12:40 PM

Update; So I ended up emailing Ed Thomas from Deep Space Products asking if he has dealt with the issue during the hypertune process. He recommends to forgo the lapping procedure. He mentioned that it must be done in place. I'm not sure if that is because there is no way to actually take out both gears completely, or there is just no easy way to remount the gears after taking them out. I sent a reply asking what he thought about designing and building a fixture at the shop I work at specifically for lapping my gears. Currently waiting for a reply. He also mentioned that over tightening the clutches can deform the ring gear enough to cause backlash and setting the gear mesh is best done with the clutches released. Regardless of all the lapping talk, I've decided to do the hypertune during the next full moon and I'm really looking forward to doing that and having a better performing mount!!
Thanks to everyone so far.


All of the gears do come out of the mount. If you can make a high precision jig to hold the ring gear and the worm in the correct position, this would be a much better way to lap the gears. However, the jig has to be very good so that the worm is centered vertically on the ring gear and has no tilt. The other problem with this is that it assumes that the worm housing is straight and level when attached to the mount. That is by no means the case. That's why in situ lapping may be better. I have this problem when installing high precision gear sets. The gear sets are hobbed and lapped on a jig that places them in the correct position. Unfortunately, when you go to install them in the mount, additional hobbing and lapping can end up being required to custom fit the gears to the mount. A hobb is much easier to use since it gets the job done in a reasonable amount of time, but the hobb has to be custom made to match the worms being installed.

Making a custom jig may be a lot of work for only two gear sets and may still not give you the right results when the gears are reinstalled. Because of the precision (or lack thereof) in the mount housings, in situ hobbing and lapping is generally going to be the best, but doing so involves taking the mount apart and putting it back together numerous times (e.g., when changing grits) which is a pain. It also presents a problem in regard to driving the worm during the process. The hobb can be made with a longer shaft, but lapping requires a flexible connection to the worm shaft so that you can attach an electric drill to turn the worm (do not lapp using the mount motors). This can be done with some rubber tubing, but from experience, I can say that it can be frustrating.

#9 John Carruthers

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Posted 23 May 2013 - 01:03 PM

you mark the worm and wheel so they go back in the same relative positions after the lapping process and cleaning.
The work is done on the mount, in situ.
Yes the lapping oil is an extremely fine abrasive, finer than polish.
Be very sure to clean out all traces before reassembly.

Sprung worms will remove any play in the worm mesh IF the springs are strong enough to overcome the tendency of the worm to climb the wheel teeth. There will still be backlash in the gear train. belt drives or friction drives can help.

Loading the mount to one side or the other only takes up worm mesh and then only as long as the the drive doesn't reverse.
Try it yourself, load the mount and see which way the worm tries to move, it moves longitudinally (end thrust*). No rotation goes beyond the worm to the rest of the gear train.

*One good reason to fit angular contact bearings on the worms, to resist both axial and radial loads.

#10 EFT

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Posted 24 May 2013 - 10:12 AM

The worms in the CGEM DX are not spring loaded. That's only in the CGE Pro. There is no practical way to spring load the worm in the CGEM/CGEM DX mounts.






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