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Eye Master
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4,185 Posts
bedding for M-1A

Tom,

We've been conversing in other forums recently.

In your response here, you talk about 'skim' bedding, 'flooding', and 'final' bedding. These sound like three distinctly different operations, versus most of the instructions out there that sort of suggest to smear it on and clamp it together for an M-1A.

Could you elaborate on what the differences are in these bedding techniques, or do they only apply to a Remington 700?

Thanks,

Art
 

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Eye Master
Joined
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4,185 Posts
Bedding

Tom, et al,

My background is an engineer in package design and prototyping. When we want to make a prototype of an injection molded part, rather than spending thousands on a steel injection mold, we can make a small mock-up using milling machines, clay, glue, whatever, then we cast that in RTV (silicone). After we cut open the silicone and extract the original part, the silicone cavity can be used as a mold. We pour urethane or epoxy compounds into these molds to create duplicate parts. On one or two projects, I have cast high precision parts using Devcon aluminum fill epoxy. I've never cast as thick as peanut butter materials, but close.

The big trick to getting excellent surface finish is degassing. When you mix your epoxy halves, you will entrain some air. This is especially true if it is more viscous. What we typically do is take the paper cup of mixed resin and put it in a vacuum chamber, making sure the cup is no more than about 1/3 full. You then pump the chamber down. As the pressure drops, all the tiny bubbles which are trapped in the mix will expand, and the mix will actually begin to foam as they float to the surface (hence the free space we leave in the cup). After about 2 - 3 minutes of foaming, all the tiny bubbles will be gone, and the foam begins to collapse back on itself. Once this happens, you can release the vacuum, and you are left with a cup of material which has zero bubbles in it. If you then apply this carefully to avoid re-introducing bubbles, you will get a bed which is bubble free.

In the event that your material is too thick for the bubbles to float out under vacuum, we also use a technique where you cast your part, then put it in a pressure chamber, slap about 80 PSI on it, and hold that pressure for 24 hours to let it cure under pressure. The pressure collapses the bubbles down to way small size. Just make sure you keep pressure on until after the glass sets up, or the bubbles will try and re-expand before the glass is strong enough.

Granted, I have nice lab grade vacuum pumps and chambers which the average gunsmith doesn't own, but I think you can get by:

You can buy small hand vacuum pumps, where you squeeze a grip with a little piston/cylinder arrangement. I think these are about $ 75 from a Cole/Parmer or a VWR Scientific catalogue, I think you can get it for 1/2 that from a surplus place. If you mix your epoxy up in an old glass jar, you can probably fit an airtight barb fitting from Home Depot into the lid, so you can mix in the jar, screw the lid on, and pump it down.

For a pressure tank to fit a rifle, you could try some schedule 40 pipe and a couple of pipe caps/bung screw. Drill/tap a small fitting so you can connect a valve so after you pump it up, you can close the valve. If you are real cheap, you can just drill a hole and fit a tire stem from a car. Put your glassed up rifle in there, screw on the plug, and pump it up with a small air pump, or even a foot operated bicycle pump. Just make sure it is schedule 40, which is rated for that pressure.

I might end up using some of these techniques myself, as I am not allowed to bring guns to work. Maybe I'll have to borrow some equipment for a weekend.

Art
 
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