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Polishing a Worm!

Started by JoseBorrero , Dec 18 2012 09:02 PM
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31 replies to this topic

#1 JoseBorrero

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Posted 18 December 2012 - 09:02 PM

Any suggestion? Pro's? or Con's?

Thanks for your help

#2 CharlesW

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Posted 18 December 2012 - 11:08 PM

Pistol owners spend substantial amounts of effort polishing the surfaces inside the feed and slide systems to improve shooting accuracy. I can only imagine that polishing the gears inside a telescope drive couldn't do the same, as long as the material removed didn't increase slop.

#3 Hilmi

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Posted 18 December 2012 - 11:08 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.

#4 MHamburg

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Posted 19 December 2012 - 09:14 AM

Talk with Ed Thomas at Deep Space Products.
Michael

#5 EFT

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Posted 19 December 2012 - 09:20 AM

The problem with polishing a worm simply using a polishing wheel or something else is that polishing is actually removing metal from the surface of the worm. A worm is cut using using a tool that forms it to the specific tooth shape desired (essentially the negative of the cutting tool). By polishing you are essentially cutting the worm with a tool that is not the shape of the cutting tool. In a realatively low precision worm this is unlikely to make a lot of difference (positive or negative) if you do not go too far with it. However, on a high precision worm you risk increasing the periodic error of the worm by reshaping its surface.

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 Hilmi

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Posted 19 December 2012 - 09:55 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?

#7 mayidunk

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Posted 19 December 2012 - 10:17 AM

Perhaps inadvertently changing the pressure angles on the worm may induce uneven wear on the pinion gear over time, causing it to develop increasing periodic error? I would check with Hollywood Machine first, before doing this.

Hollywood General Machining, Inc.
1033 N. Sycamore Avenue
Los Angeles, California 90038
323-462-2855 FAX: 323-462-2682

#8 EFT

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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 Hilmi

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Posted 19 December 2012 - 02:20 PM

I didn't have a polishing pad that tiny! No, I just smoothed out the rough edges on the surface. Didn't change the angle of the teeth. I doubt I could have even if I wanted to, this is because I don't have any polishing pad that tiny. The combination of polish and polish pad which I had couldn't remove that much material anyway. I used very very mild chrome polish and the standard dremel polishing pad. My Skil rotary tool was set to no. 1 or no. 2 on the speed dial and I made sure the worm could spin freely as I polished it, thus avoiding polishing any one place for too long.

#10 Geo.

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Posted 19 December 2012 - 03:11 PM

Even lapping helically cut worm wheels such as are found on Meade mounts made in the last 20 years won't improve things.

#11 gdd

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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 orlyandico

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Posted 19 December 2012 - 06:24 PM

well i don't know but i tried lapping the Aeroquest worm on my CGEM... (by putting toothpaste on it, putting it back on the mount, then turning the worm slowly with a drill for half an hour).

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 blueman

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Posted 19 December 2012 - 07:18 PM

Polishing is only doing one part, the worm. Lapping is matching the two parts together, Worm and Wheel.

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 JoseBorrero

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Posted 19 December 2012 - 08:04 PM

Thanks Hilmi my question came out from this website :waytogo: Also I just installed the OPW-G11 without the worm :( wasn't in stock. I reinstalled without any polish if don't like the the improvement then will go with a new worm.

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 JoseBorrero

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Posted 19 December 2012 - 08:10 PM

I'll appreciate everyone input, I just need a test :waytogo:

#16 John Miele

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Posted 19 December 2012 - 09:00 PM

Man...you guys are sure serious! I was thinking of so many funny ways to answer this question...but now I'm afraid I'd thrown out of here iffin I did... :roflmao:...John

#17 Hilmi

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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 neilson

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Posted 20 December 2012 - 12:55 AM

Hi,
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 Raginar

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Posted 20 December 2012 - 04:57 AM

I think +/-5 arcseconds is probably not realistic +/-15 is probably realistic. But you can use things like PEC and guiding to reduce it to a manageable level.

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 gdd

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Posted 20 December 2012 - 10:32 AM

Are the Aeroquest worms as precise as Losmandy's High Precision worms? Does anyone make a higher precision worm that will fit in the OPWB?

Gale

#21 blueman

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Posted 21 December 2012 - 02:34 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

#22 orlyandico

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Posted 21 December 2012 - 02:39 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.

#23 EFT

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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 JohnH

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Posted 21 December 2012 - 09:34 AM

My mount uses a brass worm gear onto a large aluminum one.

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 EFT

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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.
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