Polishing a Worm!
#1
Posted 18 December 2012 - 09:02 PM
Thanks for your help
#2
Posted 18 December 2012 - 11:08 PM
#3
Posted 18 December 2012 - 11:08 PM
I did read on the internet about a guy who had similar tracking issues to what I had and when he polished his worm gear, all the issues went away! Here is the link to his write up http://www.helixgate.net/raworm.html
I hope this information helps
Edit: By feeling the worm by finger as I rotate, the sharpest of the bits that where sticking out have definitely been smoothed out. But I used the mildest polish I could get my hands on.
#4
Posted 19 December 2012 - 09:14 AM
Michael
#5
Posted 19 December 2012 - 09:20 AM
In general, it is not something I would recommend playing with.
Lapping the worm to the wheel is less risky and can be done with polishing compound.
#6
Posted 19 December 2012 - 09:55 AM
I agree with you on the risks, but the way I saw it, the worm gear wasn't performing anyway and a replacement is $65 only. What's the worst that can happen?
#7
Posted 19 December 2012 - 10:17 AM
Hollywood General Machining, Inc.
1033 N. Sycamore Avenue
Los Angeles, California 90038
323-462-2855 FAX: 323-462-2682
#8
Posted 19 December 2012 - 10:41 AM
Ed,
I agree with you on the risks, but the way I saw it, the worm gear wasn't performing anyway and a replacement is $65 only. What's the worst that can happen?
If there is a replacement available, then there is certainly less risk. For many mounts, no replacements are avialable so I wouldn't risk it. The only downside with experimenting is that anything you do to the worm will impact the worm wheel (which is usually softer metal), for which a replacement may not be available.
BTW, just smoothing the surface of the worm is not likely to cause trouble. Its when you get into the tooth face that you can cause problems.
#9
Posted 19 December 2012 - 02:20 PM
#10
Posted 19 December 2012 - 03:11 PM
#11
Posted 19 December 2012 - 05:44 PM
Lapping the worm to the wheel is less risky and can be done with polishing compound.
Will lapping the worm to the wheel reduce PE, or will it only make the worm smoother and get rid of some of the high frequency noise?
Gale
#12
Posted 19 December 2012 - 06:24 PM
it didn't do one *&^& thing.
The stock worm was about 30" fundamental (peak-to-peak) and the Aeroquest is 16", but lapping made no difference. maybe i should have used metal polish instead of toothpaste.
#13
Posted 19 December 2012 - 07:18 PM
Now, if the worm is bad or the wheel is bad, lapping will not fix anything. But if they are both good, the it can reduce PE and making things smoother.
Cerium is used by AstroPhysics I believe, this is what is used to polish a mirror for optics. So you want the polish to make a very smooth surface, but not cut the metal that much.
Blueman
#14
Posted 19 December 2012 - 08:04 PM
I've polished mine using a Dremel polishing pad and some mild chrome polish. I did that to get rid of some burs in the worm gear. I haven't had the chance to test the result at the scope because both my RA & Dec motors have burnt out and I am waiting for Scott Losmandy to send me replacements (which he agreed to do for free).
I did read on the internet about a guy who had similar tracking issues to what I had and when he polished his worm gear, all the issues went away! Here is the link to his write up http://www.helixgate.net/raworm.html
I hope this information helps
Edit: By feeling the worm by finger as I rotate, the sharpest of the bits that where sticking out have definitely been smoothed out. But I used the mildest polish I could get my hands on.
#15
Posted 19 December 2012 - 08:10 PM
#16
Posted 19 December 2012 - 09:00 PM
#17
Posted 19 December 2012 - 11:31 PM
Also I just installed the OPW-G11 without the worm wasn't in stock.
If I recall correctly, OPT had them in stock last time I checked.
#18
Posted 20 December 2012 - 12:55 AM
What kind of PE should be expected from a brand new G11 with Gemini 2 out of the box. From what I have read in several places about 5 arcseconds peak to peak. Can anyone verify this.
I know how to lap valves on a car when doing a valve job, but how do you lap a worm.
neilson
#19
Posted 20 December 2012 - 04:57 AM
http://goo.gl/yrRXj
Here is a link to a thread from a few years ago on the subject. Looks like most people were experiencing stock PE of < +/-10. Again, really good compared to the CGEMs and iEQ45s.
#20
Posted 20 December 2012 - 10:32 AM
Gale
#21
Posted 21 December 2012 - 02:34 AM
Not recommended if you do not know for sure you can do this sucessfully.
Blueman
#22
Posted 21 December 2012 - 02:39 AM
But it's only $100.
The only higher-precision worm that I know of for the G11 is the Ovision worm. That one is I believe +/- 3" but it costs $500-ish.
#23
Posted 21 December 2012 - 09:34 AM
The worm is driven at a slew speed while engaged with the wheel and a polishing compound is applied. The lash should be set before doing this. Then when the parts are lapped in you would completely clean them and grease them and set the lash again.
Not recommended if you do not know for sure you can do this sucessfully.
Blueman
I can tell you that this process is a complete pain. What you should do is use a couple of different lapping compounds followed by a polishing compound. Between each compound and after the final compound, everything must be completely disassembled and carefull cleaned and then reassembled. In general, for most people and mounts, this process is not worth the results.
#24
Posted 21 December 2012 - 09:34 AM
I did a test years back to see what kind of periodic error was present by deliberately pointing the mount away from true north and letting stars drift across the film plane.
I noticed there was a weird periodic variation that damped out after about 15 minutes. I occurred to me this was due to the upper part of the worm gear getting dusty and tarnished, giving rise to a slight change in the drive rate over the course of the worm making a number of rotations, gradually cleaning itself off
#25
Posted 21 December 2012 - 09:36 AM
Gale, my Aeroquest worm is only +/- 8"
But it's only $100.
The only higher-precision worm that I know of for the G11 is the Ovision worm. That one is I believe +/- 3" but it costs $500-ish.
Your worm is actually a higher precision than that. It is the rest of the system that is giving you the +/- 8" accuracy. The Aeroquest worms are made to a precision of +/- 2.5 arc sec. accuracy.