Syntactic foam as a gun building material

I didn't remember that we checked it. You know, I just remembered that I have some syntactic dough that we never tried. Wonder if it's still good . . .

I tried the syntactic dough (also called "tooling foam") last night. It's a free sample that I got well over a year ago from United Resin Corporation http://www.unitedresincorp.com/casting.htm

It comes as two bags containing moist powders. When mixed and kneaded together, they produced a light, tacky dough. I shaped it into a simple patty and left it out overnight. This morning, it had hardened to about the consistancy of a soft wood. I could cut a piece off with a utility knife, but it took a little effort.

I'll have to measure a piece to verify, but the specs say the specific gravity should be about 0.5 g/cc, and it does seem pretty light.

I can see that it might be useful if you wanted to fill a space where a liquid might cause problems. You could easily pack it inside a hollow handle, for example, without getting any into places where you didn't want it.

Quote from Tin Man

I'll have to measure a piece to verify, but the specs say the specific gravity should be about 0.5 g/cc, and it does seem pretty light.

Best I can measure, the density is about 0.59 g/cc. It set up a little harder since this morning. It now carves and sands about like wood, and seems pretty tough.

One thing we forgot to mention, if you plan to shape a gun out of this stuff, you MUST make sure you have a way to keep it straight while the carbon fiber is setting up. This is easy enough for simple shapes, but gets challenging for more contoured designs.

Yea, we learned that one the hard way.

And UHMW tracks grow at the curing temperature of epoxy . . .

The donated gun was made from a purchased block.

The temporary piece at the muzzle was attached with a single screw down the centerline. This was only a dummy, so that we could later remove it and be left with an inside void to insert the muzzle.

The large piece at the back was attached with two screws through the ballast holes. The screws were removed after molding the carbon fiber, but the Delrin stays. This is where the trigger mech gets installed.

The reinforcements at the handle and reel were held in place with two small screws, just to keep them from moving while we were laying up the carbon fiber.

Although epoxy doesn't stick very well to Delrin, it would probably hold long enough. Screws are just usually easier.

Sorry. I thought I had posted the pictures of the core for the donated FRA gun.

Quote from seaweed

Pretty good idea. If you can mix some fibers, and have them bond well, into the foam you might get some increase in tensile/bending strenght.?

In principal, yes. But the glass fibers also increase the density, which is not generally a good thing if you need a lightweight core to balance out the heavier carbon fiber composite.

Quote from seaweed

What do you mean by keeping it straight?

A long, narrow piece of syntactic block is not as stiff as wood. It needs to be clamped with strongbacks to keep it straight while the epoxy / CF cures. Especially if you are including a built-in Delrin or UHMW track, because the temperature of the curing epoxy will cause the track to grow, which causes the stock to want to bow.

Quote from seaweed

Do you think this can be a way to overcome the warping and aging time associated with wood?

I'm not quite sure I understand what you mean. Are you suggesting wrapping carbon fiber around a wood gun?

Quote from seaweed

Also do you guys vacuum your guns?

No. We use heat shrink tubing. I'm sure that vacuum bagging would be better, but heat shrink is cheap and easy. Same as I did for my hybrid tube.

Dan, the best way to figure it out will probably be to see how much weight you can add to the gun without sinking it.

With the barrel ID and length Jeff or I could then figure out whether or not it would still float if filled with syntactic.

I'm assuming that the barrel is currently filled with air.

I agree. We need to know two things.

First, we need to know how much extra weight it can float. As Chad said, you can easily figure this out by attaching fishing weights with rubber bands, or something similary.

Then we need to know the internal volume. If it is a straight cylindrical bore, then we just need length and inside diamter. If that barrel is not straight (is it wider in the middle?), then you would probably need to measure the internal volume directly by removing a plug and filling it with a measured amount of water.