Making thin copper gaskets

On Sun, 31 May 2009 22:47:33 -0500, Martin H. Eastburn wrote:


"Cox" no longer exists. Estes owned the brand but didn't do anything with it but sell ever less well made and harder to find .049s. They recently sold a whole warehouse full of stuff to a distributor, although it's not clear whether they sold the Cox name to go with it.
Besides, I'm making the cylinder, head, rod and piston as a training exercise. So it may not have _exactly_ the same dimensions as the original. (It may not run, either -- I just noticed tonight that I had a pretty serious boo-boo in the port timing. I'm going to finish it off and give it a whirl; I plan on cheering if the engine can turn under it's own power. Then I start working on the next one with an eye to all the lessons I've learned on this one).
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Tim Wescott wrote:

Tim, can you get copper foil with an adhesive back in the right thickness? If so, a few seconds with an Exacto knife would trim a piece in place. The foil we used in manufacturing was fairly thin, and stood up to a hot soldering iron.
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wrote:

The copper tape for repairing circuit boards is easy to cut into complex shapes with a razor knife. I've tuned the matching stubs on stripline circuits with it; cut off a sliver, check it on the network analyzer, the engineer recalculates the dimensions, etc, over and over until he gives up. The copper does NOT come off Duroid easily.
For gasket shapes you can carefully trace around the housing with the knife. It's easier when the housing is steel but I recently cut a Kynar film to match an ABS form without gouging it. I think you could turn a lathe fixture that would clamp the sheet between two plugs to cut the OD, then a hollowed piston and a cylinder with a narrow internal ridge at the end to clamp the gasket disk while you trim the ID against the hole in the piston.
jsw
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Jim Wilkins wrote:

I had to align our ultra low phase noise synthesizers at Microdyne. They bought some plated brass strip stock for the job, but I preferred the scrap carrier strip from the smaller AMP & Berg terminals, from the crimping machines. I used a sharp pair of scissors to trim the tails left by the terminals. I would tin the ground trace & end of the inductor of the 510 MHZ VCO, and both ends of the strip. I would take an initial frequency measurement, then solder the strip to the pair of traces, to shorten the inductor. After a while, I was within specs the first try. Since the adjustment was made at the cold end of the inductor, a pair of hot Edsyn 'Loner' soldering irons let me retune the board without powering down.
We used several types of self adhesive copper tape to make sure the machined RF housings had a good RF tight seal. Some was applied to the face of one part, and trilled around the edges with an Exacto, and others went over the outside off the seams, after everything was together. of course, to get the width you needed meant something almost twice the width, so over half a roll was scrap. :(

That's a lot simpler than making a custom set of punches. :)
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Understand Tim.
I'm building - slowly - a bench top size IC engine - a 6-cycle unit. It is a scale unit and I have to make everything myself also.
Making rings is going to be interesting.
Martin
Tim Wescott wrote:

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| On Sun, 31 May 2009 22:47:33 -0500, Martin H. Eastburn wrote: | | > Tim Wescott wrote: | >> I need to make some head shims/gaskets for a Cox .09 that I'm working | >> on. These need to be of thin copper or brass, round, with an OD of | >> about 9/16" and an ID of about 1/2". | >> | >> Any suggestions on cutting them out evenly so that they're neither | >> burred nor bent when I'm done? | >> | > That seems doable. Buy a stack of brass shims - sheets of brass. | > | > Then select a hole punch of 1/2" and 9/16. These are used on paper, | > plastic, leather and the like. The trick will be a firm enough backing | > that allows a punch and won't distort. | > | > You can make these - mount them in a drill press and press downward... | > | > Grind pipe or tubing and harden if possible - maybe using an additive. | > | > Or buy them from Cox for your engine :-) Martin | > | "Cox" no longer exists. Estes owned the brand but didn't do anything | with it but sell ever less well made and harder to find .049s. They | recently sold a whole warehouse full of stuff to a distributor, although | it's not clear whether they sold the Cox name to go with it. | | Besides, I'm making the cylinder, head, rod and piston as a training | exercise. So it may not have _exactly_ the same dimensions as the | original. (It may not run, either -- I just noticed tonight that I had a | pretty serious boo-boo in the port timing. I'm going to finish it off | and give it a whirl; I plan on cheering if the engine can turn under | it's own power. Then I start working on the next one with an eye to all | the lessons I've learned on this one). | | -- | http://www.wescottdesign.com
Here's one made of brass with the correct ID but larger OD. Each sheet is .002" thick. Just trim the OD as necessary for your needs.
http://www.mcmaster.com/#shim-stock/'hiyu
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|| On Sun, 31 May 2009 22:47:33 -0500, Martin H. Eastburn wrote: || || > Tim Wescott wrote: || >> I need to make some head shims/gaskets for a Cox .09 that I'm working || >> on. These need to be of thin copper or brass, round, with an OD of || >> about 9/16" and an ID of about 1/2". || >> || >> Any suggestions on cutting them out evenly so that they're neither || >> burred nor bent when I'm done? || >> || > That seems doable. Buy a stack of brass shims - sheets of brass. || > || > Then select a hole punch of 1/2" and 9/16. These are used on paper, || > plastic, leather and the like. The trick will be a firm enough backing || > that allows a punch and won't distort. || > || > You can make these - mount them in a drill press and press downward... || > || > Grind pipe or tubing and harden if possible - maybe using an additive. || > || > Or buy them from Cox for your engine :-) Martin || > || "Cox" no longer exists. Estes owned the brand but didn't do anything || with it but sell ever less well made and harder to find .049s. They || recently sold a whole warehouse full of stuff to a distributor, although || it's not clear whether they sold the Cox name to go with it. || || Besides, I'm making the cylinder, head, rod and piston as a training || exercise. So it may not have _exactly_ the same dimensions as the || original. (It may not run, either -- I just noticed tonight that I had a || pretty serious boo-boo in the port timing. I'm going to finish it off || and give it a whirl; I plan on cheering if the engine can turn under || it's own power. Then I start working on the next one with an eye to all || the lessons I've learned on this one). || || -- || http://www.wescottdesign.com | | Here's one made of brass with the correct ID but larger OD. Each sheet is | .002" thick. | Just trim the OD as necessary for your needs. | | http://www.mcmaster.com/#shim-stock/'hiyu |
Or these : http://www.mcmaster.com/#shim-stock/'hnpy
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Tim Wescott wrote:

Cut your shim stock in 1" squares. Cut more than you'll need in a lifetime. The more the better.
Stack them up and sandwich them between 2 pieces of AL about 1/8" thick. Clamp well, drill through the center then bore to the ID.
Turn an arbor for your lathe that will just fit inside the ID. Drill and tap a hole in the center of the arbor. Make some sort of end cap that will hold the gaskets and AL snugly on the arbor.
Chuck the arbor in your lathe and turn the whole mess down to the OD.
It won't take as long as it looks. I've done the whole thing in about 1/2 hour.
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On Mon, 01 Jun 2009 10:07:56 -0700, Jim Stewart

Why not try a car/truck parts shop? A copper seal ring with an I.D. of 1/2 inch ought to be available as they are commonly used on cars and trucks and diesel injection systems.
Over here you can go into a shop selling car parts with your part in hand and tell 'em I need a copper ring to fit here. Usually get it too. :-)
Cheers,
Bruce in Bangkok (bruceinbangkokatgmaildotcom)
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