All,
I was thinking about the design and was concerned about dust/dirt gettign into the clutch and keeping the surfaces from contacting eachother and I also want to improve the coeffficient of friction. So I began to think about products and applications where high friction is needed to see if I could find something that woudl work well for this application. The first thing that came to mine was non-skid tape that you can put down on steps and stuff. That is like very tough sand paper, which would really improve the surface friction without creating any "sticky" adhesive like sufrace so that when the pressure is released, it doesn't stick. I was prepared to make a desing with this and accept the potential marring of the surface of the clutch plates, which isn't a real big deal, but it will wear more quickly. However, I found non-abrasive non-skid tapes as well and they are pretty cheap.
I want something that is rubber coated, textured, and thin. Rubber increases friction coefficient and is somewhat compliant to flex around anything that gets in the clutch. Texture helps air get behind the plexiglass to release when pressure is taken off and gives dust somewhere to go/collect that doesn't affect the gripping power. Thinness is beneficial because I don't have a lot of room but rubber is also very flexible and shears a lot under load... the thinner the tape is, the less it will shear under load which has the net result of making the joint stiffer.
I found handrail grip tape that seems to meet the above requirements. I found a couple that I may end up using. Here are a couple pictures of the textured surface.
This is 3418 Anti Slip Tape from AntiSlipTapeShop.com:
- moulded, pimpled surface grip tape
- 3418 Anti slip tape.jpg (14.2 KiB) Viewed 17445 times
This tape has a moulded surface that is a bunch of domes... It is much like a ping pong paddle surface (and yes I looked at that too... it was very expensive for what you get). It is 0.023" thick and will have the advantage that all the dome heights should be very uniform, so it should allow for good, uniform contact. A 52"x12" piece is $13.20 with free shipping.
The second one I found was Black Resiliant Grip Tape:
- Black Resiliant
- BlackResilientGripTape.jpg (16.05 KiB) Viewed 17445 times
The surface does not look that uniform, which could cause some problems, but I don't know what scale this is. It is thinner than the other stuff, 0.02", but not much. They do say thaat this is the most grip for a non abrasive tape. a 47"x12" piece is $11.00
Either option will give me more than enough material to get all the clutch rings I need and they are adhesive backed with really strong adhesive.
Does anybody have any other suggestions?
Here's a view of the shoulder clutch with the tape in place.
- Shoulder Clutch Update 2
I added slots in the inner clutch plates to help air get in behind the clutch so they release quickly and easily (may also help bite the tape when pressure is applied). I conservatively estimate the coefficient of friction to be about 1.5 with these materials, but it is likely to be much higher. At that kind of friction, I actually only need 1/2 the plates in the clutch. However, I don't want to end up putting too much stress on the plates and get cracks. Plus this gives a margin of safety.