questions about composite rifle stock fabrication

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#1

I have begun manufacturing of a composite rifle stock for what will soon be a larger scale production. They are currently being laid up in one piece, a bladder inserted and inflated to approximately 20 lbs. Material is epoxy and E glass, but there is still a decent amount of finish work required in the flashing or partition area I would like to try to reduce. The stocks are produced as one part for strength, not two parts fused.

I have been struggling with a few things; first is the bladder material to use. Currently we are using SL-800 fused together, a rubber plug as a stop in the butt of the stock and the bladder inflated after layup. I have been able to get about 5-6 runs out of the bladder, not bad but not good enough for production. I think there is a fair amount of excess resin that can be removed with a bladder capable of higher pressure, resulting in a stronger and lighter part. I am seeking a better material or method for the bladder.

The second concern is the life of the mold, which seems to start to fail in areas after 10-15 part cycles. The original molds as pictured are a 2 part mold made of polyester resin and tooling gel coat, the partition line isn’t straight, but that is not a issue. We are using a quality semi permanent sealer and release agent, and applying additional release after 3-5 parts. I am considering trying a semi rigid polyurethane mold inserted in a rigid fiberglass mold in hopes to get a longer mold life.

Last question; I want to produce carbon fiber and Kevlar versions of this stock, and wondering what would be the best way to make the partition look good, since it will be a cosmetic part. Currently, the production parts are made by tinting the epoxy gel coat, so little care needs to be taken during layup to ensure the material is straight.

Any input would be appreciated

#2

SO you can get rubber bladders made. You have to provide a male plug so they can dip it to make the bladders. Or you could use vacuum since you’re only using 20psi of pressure. Honestly you shouldn’t need very high pressure and vacuum is more than adequate. And a mold for vacuum doesn’t need to be as strong.

As you’re saying, the molds you have are degrading because of the pressure. I could see that especially with the polyester molds. You could either make the mold stronger… thicker, more material, epoxy, etc. Or get production type molds machined out of aluminum. We use aluminum molds with either bladders or silicone intensifiers and they handle the force. Though we do make our parts like this in a press, so you’d have to have enough bolts and a thick enough mold to take this stress. Aluminum might be more pricey than making your own polyester molds… but if you figure the cost after making 200+ parts, it’s probably worth it. Plus you can switch to prepreg if you have a metal mold and get a faster cure time with a heated tool. Like anything, depends on what you want to invest and what you plan on getting for each part.

And if you want a raw carbon part with a minimal seam, you’ll want good molds. MOlds that fit together nicely. Again if you machine aluminum molds this should be no problem. You can also use a braided sleeve instead of broad stock and you won’t have any overlaps.

Cool looking part though… I’ve wanted to make a carbon gun stock. Which rifle is this for?

#3

you can easily make new DIY corian molds that are super strong from your current molds …

i use garbage bags for bladders, but i only get one part from 1 bag as the bag comes out in pieces, i have pumped to 3 bar with a very nice finish

#4

This is a production stock that comes out of the mold with no inletting. It is designed to take nearly any action, Tikka, Remington, Winchester, etc, short or long action. We determine the barrel channel, bottom metal or trigger guard, and action and it is milled out.

Who would I inquire about making rubber bladders? That is a great option. I thought of making a shell of both sides and not joining them, this would allow me to join the sides and pour and roll around liquid rubber or silicone into the cavity. Separate the sides and I should have a fairly rigged bladder.

#5

I can’t remember the companies that do bladders… there are a few around. There’s been multiple threads on this exact subject of bladders; maybe search them out first.

There are silicone products that you could also try. There are some paint on silicone that may work? Or maybe the spray on vacuum bagging silicone might do it?

though if what Blakcrat is saying works, I’d try that. 45 psi is pretty darn good. And I know that ldpe sheet is very cheap.

#6

piercanusa.com will make custom latex bladders off a stock shaped tool that you provide them with. check out their site.