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Slip Clutch Material

ATM DIY EQ Mount
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19 replies to this topic

#1 matt_astro_tx

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Posted 25 February 2021 - 11:29 AM

Started working the mechanical aspect of my DIY EQ mount upgrade to add RA tracking.  I decided to tackle the worm gear and clutch assembly first since it's a self-contained unit.  I've acquired socket head bolts and die springs for the clutch plate to provide compression to the clutch assembly, and now I'm deliberating on the clutch material itself.  I've read suggestions on CN for everything from cork to leather to plastic.

 

What are your suggestions for ideal slip clutch pad material?  (It will be a dry clutch)

 

I'm considering sheet cork cut to size such as one of the two products below:

Thanks!

 

EDIT:  Forgot to mention the space between the gear face and clutch plate (for the pad material) is 1/8"

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Edited by matt_astro_tx, 25 February 2021 - 11:31 AM.


#2 Couder

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Posted 25 February 2021 - 11:41 AM

I 've seen cork, Teflon, plastic, and leather. None of it is very expensive, although they all have very different characteristics. You might try the cork first. Leather works well and might hold up longer, but make sure it is even thickness. If one doesn't work out, try another. This picture is an Edmund mount I had, it used the Teflon.

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#3 Mike I. Jones

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Posted 25 February 2021 - 11:54 AM

I used the side of an empty gallon jug of Clorox and it has worked great over the years.  Cut the bottom and tapered top off with scissors, roll the center section out flat, carefully play heat from a hair dryer on it to reduce curling, and cut your clutch annulus out with a box cutter.


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#4 mashirts

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Posted 25 February 2021 - 12:17 PM

I have that thin cork material.  Worked great on a criterion 1 inch EQ I once owned

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#5 Supernova74

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Posted 25 February 2021 - 12:33 PM

Have considered useing something like nitrile bonded rubber cork,it’s similer to cork however it has composite rubber elements in the material it,s basically used for head gaskets etc.cork sheet might work however I can see it failing in time as has no flexible quality’s.there also is another material called oil resistant nitrile rubber this is black and very tacky when felt which is used for anti slip type applications.



#6 dan chaffee

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Posted 25 February 2021 - 12:38 PM

You could buy  bicycle brake pads and slice them to thickness.  It would last....



#7 scadvice

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Posted 25 February 2021 - 12:58 PM

I use this for the clutch plates. It works very well with no dirt and dust collecting like oiled cork or the old style oil soaked gasket materials.

 

https://www.mcmaster...log/127/3912/


Edited by scadvice, 25 February 2021 - 04:32 PM.


#8 matt_astro_tx

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Posted 25 February 2021 - 01:42 PM

Seems silly, but I just realized I need to put slip pad material on both sides of the gear.  Like the illustration below.

 

Previously I had been focusing on having 1/8" of clearance for the pad between the gear and the clutch plate and had been looking for material of that thickness.  But with my realization, I need to be looking for 1/16" material to place on both sides.  Right?

 

Sorry guys, this is my first foray into telescope clutches and haven't found a good guide online. Thanks for your wisdom.

 

Given all that, I think I'll purchase some of the cork gasket material mentioned as it happens to be 1/16" thickness.

https://www.amazon.c...l/dp/B000CNBVVM

 

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#9 PETER DREW

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Posted 25 February 2021 - 02:44 PM

Our huge Ealing-Beck equatorial mount uses cork clutch pads.



#10 matt_astro_tx

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Posted 25 February 2021 - 02:48 PM

Any pictures of the E-B?



#11 scadvice

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Posted 25 February 2021 - 04:31 PM

Most of these ideas of material will work but with the gasket material to get a smooth and even torque release the material needs to be oil soaked. I transitioned to the MDS-Filled Wear-Resistant Nylon Sheets to avoid using oil. It comes in various thicknesses.

 

https://www.mcmaster...log/127/3912/  

 

Whoops looks like the link was wrong in the first post. I fixed it.

 

Yes, both sides. See the pictures of my current project mounts clutch for the RA. The felt pin marked disc is a torque testing disc where the gear goes.  Hang a line on the edge then add weights on the line until it slips to judge effectiveness.

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Edited by scadvice, 25 February 2021 - 04:34 PM.


#12 matt_astro_tx

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Posted 26 February 2021 - 10:27 AM

Thank you for the pics and advice! That’s a great looking assembly. Since I’ve already got cork sheet on the way, are you saying I need to soak it in oil?

#13 scadvice

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Posted 26 February 2021 - 01:39 PM

I've oil soaked most of them but I know people who use them dry. So maybe you could try dry first. I just used 30 wt  motor oil 50/50 mixed with acetone to help it soak in. Then let it sit for a day on newspaper outside or in a warm sunny spot for a few hours to evaporate the acetone. dried them with cloth before using.



#14 don clement

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Posted 26 February 2021 - 01:52 PM

Since I am going thru the same problem of choosing a clutch  and clutch material for the Dec axis  with HDPE worm gear I thought it would be good to post a disassembled Byers clutch that is being used for the RA axis. A couple of things to note about Byers clutch is that he pins the two clutch plates and spring loads the clutch. I really like Turcite that I have used before as clutch material that can be used dry. https://www.boedeker.../Family/turcite

 

 

Don

 

HPDE worm gear for Dec axis

IMG_6386Web.jpg

 

IMG_6405Web.jpg

 

IMG_6400Web.jpg

 

IMG_6414Web.jpg

 

IMG_6411Web.jpg

 

IMG_6416Web.jpg


Edited by don clement, 26 February 2021 - 02:00 PM.


#15 matt_astro_tx

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Posted 26 February 2021 - 01:56 PM

Appreciate the pics! I’ll be spring loading mine. Here is the clutch assembly in its current state. 

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Edited by matt_astro_tx, 26 February 2021 - 01:57 PM.

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#16 Scott E

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Posted 27 February 2021 - 01:12 AM

I used a plastic gallon milk jug. Not sure if you can find a large enough flat surface but it may not matter. My split-ring equatorial uses a small cone clutch for RA and a long strip wrapped around a ring for DEC. It has very low friction so you'll need more pressure than for cork, but it is EXCELLENT for stiction. Breakaway friction is essentially equal to dynamic so when you start pushing, there is NO jerk at all, it just starts moving



#17 matt_astro_tx

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Posted 27 February 2021 - 10:13 AM

So the 1/16" automotive gasket material I purchased came and it's a fiber sheet, not cork at all, more like construction paper.  I'm going to the auto parts store later today to purchase some actual cork material.  They have two thicknesses.  1/16" and 1/8".

 

Here's my question:

 

Is it better to precisely size the slip pads to fit in the empty space between the clutch plates and gear like this such that there's a clean mating of the clutch plate to the hub:

gallery_357716_15897_15848.jpg

 

Or is it better to "oversize" the clutch pads like this?

gallery_357716_15897_5963.jpg

 

The second image makes more sense to me, but I want to be sure before I go purchase another batch of material.  Note that this will create a small gap between the hub and plate.  We're only talking about a difference of a 8th of an inch here in the total stack up.  The material I already purchased was 1/16" and appears to be too thin to be adequately compressed in the assembly to provide stiction, making me think the safer bet is to go with 1/8" material as shown in the second image.

 

Thanks



#18 matt_astro_tx

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Posted 27 February 2021 - 03:16 PM

I was able to find a pack of a variety of gasket material at the parts store that included both 1/16” and 1/8” sheets. I think it’s a decent compromise having one pad full thickness, and the other at the smaller end. Worst case I have enough material to cut two pads from each sheet of the same thickness.

 

I’ll update with how it ends up. Here’s a photo of the material I bought. 

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#19 PETER DREW

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Posted 27 February 2021 - 03:35 PM

Any pictures of the E-B?

<astronomycentre.org.uk>



#20 matt_astro_tx

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Posted 28 February 2021 - 08:49 AM

Got the clutch and gear assembly complete this morning. The 1/16” gasket cork was easy to work with and I hope will be a good solution. Wont know how it performs for several more months until the rest of the mount is complete. Now it’s on to overhauling the worm drive block which is completely seized up and machining a few other parts. Thanks everyone for your help!

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