Rotary motion to reversible linear motion
- Thread starter Brian Rupnow
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Maybe.
So, getting very close to a working module. The 1/8" cross section o-ring on the final drive shaft is going to have to be changed, as the action is rather intermittent right now, (it slips) but it does work. The simplest change would be to go to a 3/16" cross section o-ring, and tomorrow I will try that. It is a very interesting little project. I won't build the transfer cart and the rails until I get this drive working okay.---Brian
Hi Brian, Is the O-ring in a Vee groove? A Vee is the better shape for developing friction and preventing slippage - I think?
What material O-ring are you using? Some elastomers are a lower friction than plain or nitrile rubber... Viton is a lower friction I think? - Better to avoid those? - I use Nitrile, because that's what I happened to have. I think it was intended for a domestic water seal - use with a plastic fitting of some sort onto Bathroom ceramic? It didn't like any oil on the drive surfaces, but liked a little roughing of the disc surface from the Knurling tool. It gave the steel-rubber interface a "tread". - Works with very low contact pressure on my model, but yours is on a proper machine drive , many orders of magnitude greater than my steam boat drive.
K2
What material O-ring are you using? Some elastomers are a lower friction than plain or nitrile rubber... Viton is a lower friction I think? - Better to avoid those? - I use Nitrile, because that's what I happened to have. I think it was intended for a domestic water seal - use with a plastic fitting of some sort onto Bathroom ceramic? It didn't like any oil on the drive surfaces, but liked a little roughing of the disc surface from the Knurling tool. It gave the steel-rubber interface a "tread". - Works with very low contact pressure on my model, but yours is on a proper machine drive , many orders of magnitude greater than my steam boat drive.
K2
The o-ring is nitrile rubber setting in a v-groove. The face of the contact wheel has been sandblasted to give it a uniform rough surface.
Today was a good day for laying around the house doing nothing. Finally, about 3:00 I summoned enough energy to come down to my shop and start the fabrication and assembly of the long frame that the carriage rolls back and forth on. No drama--everything went as I had hoped (the rack is just setting there, not bolted down). Lookin' good so far. Tomorrow I will make the four stands that tie the long frame to the frame with the gears on it. I ordered a box of 50 o-rings from McMaster-Carr today---I only need one, so I will end up with 49 spare o-rings.
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Brian,
I am sure that you will find a use for them, in some project yet to hit the paper, The carriage looks good.
Cheers
Andrew
I am sure that you will find a use for them, in some project yet to hit the paper, The carriage looks good.
Cheers
Andrew
I would have thought that a polished surface would have been preferable...
as a rough surface should lead to rapid O-ring wear and slippage due to the drop in pressure, imo.
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Will the O-rings polish the disc over time? The PU rubber cords (not sure if that is the right word), to create small drive belts have slightly rough texture, they can be welded with a hot knife.
Assuming the gearbox is not used on a regular basis for many hours, it is probably good enough to have 49 replacements
and wait what happens.
Today was wheel day. If I've lived right, the four v-groove wheels will fit into the pockets milled in the frame they are leaning against. As far as the rubber o-ring is concerned, if it is a bit too large in diameter I can always grind it down to the correct size. This machine will never run long enough to wear an o-ring out. (if it does, I have 49 spares).
Hi ZEPHYRIN. The elastomer of the O-ring needs to be one that has good fatigue resistance as it is constantly deforming and relaxing at the contact point. A rougher surface that "grips" will probably last longer than a surface with some slip. The slippage puts shear stress on the surface, and the elastomer consequently shreds material as a result, thus creating a more rapid failure? The gripping surface suffers for random fine higher pressure points, so compressive fatigue takes place, which does not shed material until the fatigue life is exceeded, when rapid deterioration occurs. Will it last longer? So who can guess which will fail first? - I think the shear forces on a smooth O-ring, wearing the O-ring cause a quicker failure, but it really is anyone's guess, as to actual surface roughness, slippage in the smooth surface condition, Wear, tear, and fatigue of unknown O-ring materials pressures and transmitted torques. What starts out as the better option may or may not be the better option for a long life.
I really don't know which is better!
K2
I really don't know which is better!
K2
