Author Topic: O-ring as pulley belt?  (Read 986 times)

Offline kvom

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O-ring as pulley belt?
« on: July 22, 2020, 09:37:49 PM »
I want to figure out how to drive the governor on the Greene engine.  Given the fixed distance between pulleys and the given diameters of the pulleys, I determined that the nominal belt length is 21.945".  Dividing by pi gives 6.99 diameter for a circle with this diameter.  A #262 O ring has an ID of 6.984.

Any experience using Buna-N rings as governor belts?  Do these have any stretch that might make the next smaller size work (6.73 ID)?  I can always remake one of the pulleys slightly larger or smaller to fit.

Round or square cross section?

Offline Dan Rowe

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Re: O-ring as pulley belt?
« Reply #1 on: July 22, 2020, 10:07:42 PM »
My Servo drill press has an O ring for the drive belt. I just checked a new ring with the one in service and the one on the machine has streached about 1/4" in diameter. I did a crude measurement of how much the new belt has to streach to fit the pulleys and I got about 4" of belt length that a new belt streaches to fit.

This is an 1/8 O ring and the drill press has a 3mm chuck.


Offline crueby

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Re: O-ring as pulley belt?
« Reply #2 on: July 22, 2020, 10:54:37 PM »
The o-ring material can be glued with superglue (gel type is easier, doesnt wick all over the place), so you could start with a larger ring and trim it down to size till it gripped well. They do have some stretch. I have some o-ring material that came by the foot, and I just cut it straight across with a sharp knife, then a drop of glue on the ends and press them together for a few seconds till the glue grabs. Let it sit a while to cure, and it will work. Common way to make drive belts for things like Mamod engines and shop displays.

Offline Zephyrin

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Re: O-ring as pulley belt?
« Reply #3 on: July 23, 2020, 08:40:55 AM »
I use commonly O ring as belt for my engines, as I have a large stock of large dia and small section, the right tensioning is not always easy to set, too much stretched, and a lot of energy may be lost.
But for a period engine, this type of belt seems an anachronism; for a steam engine governor for instance a simple round leather lace is much nicer, but not as much as a flat and thin leather strap, IMO.

Offline derekwarner

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Re: O-ring as pulley belt?
« Reply #4 on: July 23, 2020, 12:55:49 PM »
Nitrile [NBR] elastomer has no real gluing affinity with Cyanoacrylates [Supa glue]......[the 2 halves of an O-ring may last for a very short period of time only]

Cyanoacrylates glues has little ability to flex or resist the shear strength issue when bent on axis when engaging a small radius as in a pulley

I do like the idea from Zephyrin in using a 1/8" square leather bootlace .......join with a few stitches of cotton + a Polyester type glue [Gorilla Type Brand]

The latter glue has a certain flexibility, and combined with the cotton twine +....possibly an adjustable tensioning pulley would be perfect for a period engine

Derek L Warner - Honorary Secretary [Retired]
Illawarra Live Steamers Co-op - Australia

Offline tghs

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Re: O-ring as pulley belt?
« Reply #5 on: July 23, 2020, 01:41:32 PM »
urethane belting,, better than orings,  what unimat lathe users mainly use now,, cut to length , melt the ends together,, you can even make a jig to get near perfect joints..
what the @#&% over