Rubber Discs for Shock Strut

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challenger_II

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Ok, I will throw this out and see what I reel in:

On some of the old home-builts, from the 20's, and 30"s, had rubber discs on their shock struts. Not much info, in the old plans.
I would like to know what they used. I have dimensions, but no reference to materials used (except the Corben Ace plans, but that leads to a dead end).

I need/want/desire a disc of 2-2.25" diameter, a bore of .88-.90", and a thickness between 3/8" and 1/2". Prefer a durometer of 30-40.

Thoughts? Hints? Suggestions?
 

TFF

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Catalog hunting. Grainier, MSC, McMaster Carr and the like. Ercoupe and Mooney use pucks but bigger.
 

karmarepair

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Well packing, if you can find the right size. A quick search did NOT look promising.

Or order the sheet from Grainger/McMaster Carr, etc.

Cutting it to size can be a Bee-Yatch. Grind a knife edge in a piece of tubing the bore you want, chuck it in a drill press, and use water or detergent or glycerine or commercial sex lube (no, I'm not kidding). Commercial punches are available, but they are spendy. A Forsrtner bit MIGHT work. Freezing it also helps, some.
 

GeeBee3

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try contacting a local rubber manufacturer. I worked for one long ago in my summer student days and they had sheets of rubber materials in various durometers. They can probably cut 'washers' to any dimension and thickness that you want.

GB3
 

12notes

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You need to know what scale that 30-40 durometer is in. That could either be gel, a pencil eraser, or a shoe heel hardness depending if it's Shore 00, A, or D scales. While I'm sure it's not gel-soft, either of the other two are possible.

What diameter, if there's a hole in the middle, what size? Some cars have bump stops that fit on the shocks, you might be able to find an appropriate size and hardness. Something like this (chosen at random from quick search, no idea if it's appropriate):

If you have to make your own, a diamond coated abrasive hole saw works pretty well, and freezing the rubber with dry ice makes cutting and drilling much easier.
 

karmarepair

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It's probably Shore A. The one spec I could find in Pazmany, "Landing Gear Design for Light Airplanes, Volume 1", calls for 1" think hydropress pads, compression modulus of 400 lbs/in^2, shore hardness 52. Shore D of 50 = shopping cart wheel, Shore A is somewhere slightly squishier than tire tread.
 

challenger_II

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Best lube would be anhydrous lanolin, same a s what we use for swaging lead bullets. I have looked at that option, but am holding out hope there is a ready made option!
Thanks, for the input!

Well packing, if you can find the right size. A quick search did NOT look promising.

Or order the sheet from Grainger/McMaster Carr, etc.

Cutting it to size can be a Bee-Yatch. Grind a knife edge in a piece of tubing the bore you want, chuck it in a drill press, and use water or detergent or glycerine or commercial sex lube (no, I'm not kidding). Commercial punches are available, but they are spendy. A Forsrtner bit MIGHT work. Freezing it also helps, some.
[/QUOTE
 

challenger_II

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Dimensions were stated in original post. 30 dur, is high-end "pencil eraser", and 40 duro is lower to mid "windshield wiper" by the chart I have. Each is Shore A. The only "plans spec" i have seen is for 30-40 duro.


You need to know what scale that 30-40 durometer is in. That could either be gel, a pencil eraser, or a shoe heel hardness depending if it's Shore 00, A, or D scales. While I'm sure it's not gel-soft, either of the other two are possible.

What diameter, if there's a hole in the middle, what size? Some cars have bump stops that fit on the shocks, you might be able to find an appropriate size and hardness. Something like this (chosen at random from quick search, no idea if it's appropriate):

If you have to make your own, a diamond coated abrasive hole saw works pretty well, and freezing the rubber with dry ice makes cutting and drilling much easier.
 

Lucky Dog

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Coming from the mountain bike industry, we tried a number of elastomer cushions to avoid springs and hydraulic dampers in the early days of suspension. This type of cushion, whether you use rubber discs, automotive shock bumpers or cast urethane, is limited by how much the elements can distort. (They don't actually compress, unless the element is a closed-cell foam.) The best shock bumpers are exactly that - closed cell foam, usually some sort of urethane product. To use them inside a strut, you'll need a device to center the elements (a shaft or indexed spacers between the elements), and pre-test to determine how much space you'll need around the circumference of the elements to allow them to squish outwards. The downside of elastomeric compression stacks, however, is that the spring rate tends to ramp up dramatically as they arrive at full compression. Bouncing will be an issue if you get the material/stack equation wrong. Road racing auto shock makers offer the widest selection in both shapes and spring rates - and most road racing options have better damping qualities than you'll find in off road applications. Sorry for the lengthy text.
 
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cluttonfred

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There are also thousands of commercial suspension dampers that could work. I have also seen designs where the discs are in a tube and will scrub on the inside of the tube at high deflection to provide damping. Another alternative source is the racing moped/scooter market which offers some adjustable shocks that could be tuned to suit.
 
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