Carbon fiber stock building methods?

J

Joe Woosman

Member
I've been researching methods of building carbon fiber layups. I assume the common methods used for stock building are expanding the layup to a hard outer surface.... A mold.

I have quite a bit of experience machining various foams to accurate and intricate shapes. I'm wondering if I machine a foam core and wrap it with carbon if the quality could be high. I also have the ability to produce the molds so the trade off is the time and expense to machine molds versus the flexibility of changing designs and machining them rather quickly, which I find quite appealing.

Any advice would be greatly appreciated.
 
Check into vacuum bagging over your core. I think the epoxies would eat the foam up plus you wouldnt be able to put in the cross bracing. Just a hollow shell wont be too strong unless you put it over a rigid core like wood but i like that youre ready to try something. Good luck for sure
 
I've done this over wood stocks and then milled the wood out. I've not done this with foam but have used foam for filling voids. Also modeling clay etc.... I've also made split molds by laying over stocks, taking the stocks out and then laying up the shell(s) inside the mold.

Here's what I've found.

Epoxy resins are less likely to melt foam than poly resins.
Epoxy resins are twice the money of poly resins, also much stronger.
And smell better, MUCH better.
I now use only epoxy.
Going over the outside is harder than it looks.
Saran wrap is your friend!
Resin makes weight fast.
Saran wrap is your friend.

I know I ain't much help. Because I haven't learn't much yet :)

al
 
I've watched several videos of the vacuum bagging process. They typically are sucking the material against a precision surface and the bag side isn't a good cosmetic finish. I've seen where they then sand the bag side surfaces and brush on more epoxy material, sanding and polishing to a fine finish. As Al said, "resin makes weight fast" and that concerns me for a weight critical stock.

There are foams I work with that are unaffected by solvents or epoxy so that is not an issue. These foams can range from soft to the touch to hard like wood. These foams are compressive strength rated foams and as the strength goes up, so does the weight.

Ok - Here's my Idea. Mold a box beam carbon backbone that runs the entire length of the stock with structures added to fully contact and support a glued or screwed action. Machine the outer shape of the stock from a good compressive strength foam. Inlet that foam blank for the carbon beam and epoxy that in place. Apply a thin carbon wrap over the outside of the stock to protect the foam, add a little strength and make it look good.

Please poke holes in the design at will...
 
The vacuum bagging is what makes the smooth finish and lets you use less resin. If you suck the bag down in a wrinkle itll leave a wrinkle. It keeps it tight to the form. Vacuum bagging is used currently to do the same type things youre wanting to do. laying up a carbon layer on a form its the only way to do it strong and light. Inside a mold and cooking is a different method alltogether. Check out making airplane parts like diamond airplanes. They vacuum bag the whole fuselage and one guy can carry it to the next step.
 
In other words with the foam core youre proposing any method besides vacuum bagging will double the weight of it
 
Ohhh, and the way to get the smooth finish from the mold is something called gel-coat. You make the mold very smooth and blemish free, then polish it even more and apply a polished coat of fine mold release. When I say "polished coat of mold release" I mean that the mold release need be very smooth, We're not talking about Brownell's sprayon rubber nor something that goes on with a brush nor anything reactive but something in a wax, normally organic like Carnauba based.

Externally applied jobs need be hand cut, 'blocked' and hand polished with some sort of paste compound.....like this




https://www.google.com/shopping/pro....7&ei=26c6VInFAuadjAKsvoHIAw&ved=0COwCEKYrMBE

VERY tricky stuff


al
 
Ive waxed a few boat molds. Gotta be absolutely perfect. And vacuum bagged some carbon fiber deck lids and cowls.
 
I do not think that it would be a big deal for many applications, but...there is a reason that short range benchrest stocks are not made of 100% carbon fiber....damping. Back in the day, when it was a new material, and referred to as graphite, rather than carbon fiber, famed benchrest stock maker Lee Six made a stock up of the stuff, and he never could get it to shoot. At the time, the thought was that the material was so strong and stiff that it reacted like metal, that it lacked damping. Of course this was for a specific application, that has different accuracy standards than hunting, tactical, or for that matter air rifles.
 
Boyd Allen said:
I do not think that it would be a big deal for many applications, but...there is a reason that short range benchrest stocks are not made of 100% carbon fiber....damping. Back in the day, when it was a new material, and referred to as graphite, rather than carbon fiber, famed benchrest stock maker Lee Six made a stock up of the stuff, and he never could get it to shoot. At the time, the thought was that the material was so strong and stiff that it reacted like metal, that it lacked damping. Of course this was for a specific application, that has different accuracy standards than hunting, tactical, or for that matter air rifles.
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Boyd,

Do you have anything else in your BR history database relating to stock rigidity and damping? Anything that explains why all metal rail guns work so well but bag guns are different?
 
Two of the best shooting rails that I know of, Gary Ocock's and Tom Libby's have damping provisions built into them. Also, another friend, the late great Del Bishop, told me that shooters have found that putting various materials under the barrel block, had an effect on accuracy. Currently, there are a number of examples of rails that have some sort of damping provision built in.
 
Boyd Allen said:
Two of the best shooting rails that I know of, Gary Ocock's and Tom Libby's have damping provisions built into them. Also, another friend, the late great Del Bishop, told me that shooters have found that putting various materials under the barrel block, had an effect on accuracy. Currently, there are a number of examples of rails that have some sort of damping provision built in.
Click to expand...

Interresting! Thanks for sharing that Boyd.

When I was racing dirt bikes I had a set of handlebar clamps that had interchangable urethane inserts under them. The softer inserts lowered the amount of vibrations and shock transfered into the bars. It certainly stands to reason the stock would have an effect on how the barrel vibrates.
 
Joe,
You absolutely can make a stock using the method you describe. For most people it might be the hard way, but since you have access to the foam and the ability to machine it, I say "go for it!"

Here is a thread I started a few years ago:

http://benchrest.com/showthread.php?60266-Benchbeam-Carbon-Wood-Stocks

The "core" or "skeleton" of that stock is carbon fiber laid up by hand in the wooden parts, then the action and barrel channel are lined with more carbon fiber and molded in place using a steel mandrel. The result is a carbon skeleton built into the wood.

If I had your access to material and tools, I'd substitute the wood from the stock I show with a light weight foam and then wrap the whole thing in a carbon skin. You don't have to bag or make a mold. In an ideal situation, where the resulting component is built for ultimate strength or stiffness, you might. Or in a production situation, perhaps. To just make one stock you'll just spend a lot of money on all that stuff and the result won't be any better or worse for the purpose.

So, carbon skeleton, surrounded by a foam structure for shape, then wrapped in carbon fiber, then smoothed, faired and painted. It could be great.
 
What became of the Robertson molds or methods?

My last VFS rifle was in a Robertson stock and It was the best VFS rifle I have owned to date. Whatever they had figured out worked.

Pete
 
Current state of the art carbon stocks have utilized cores of foam, expandable, foam, balsa, etc. if you go visit some of the sites for radio control gliders, for instance, you will gain a lot of information on molding, vacuum bagging, various composite cloth options as well as resins, etc. there is a bunch of stuff out there. Do not overlook some of the German sites. Some of these guys are molding some amazing ships costing many thousands with very precise attention to fit and finish. If nothing else you will learn plenty.
 
Robertson

Robertson Composites was sold about five years ago. About three years ago it was put into bankruptcy by the new owners. The assets were bought by a couple in Montana but I don't think they have been able to produce anything. I must admit that anything produced has been far off the standard of Robertson. I did do an inlet last week for a company doing a knock off of a Robertson stock and it was not a great experience for me.
 
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Having had and worked with a few of YOUR stocks its a shame it turned out the way it has, you had a very good product....
 
geo.ulrich said:
Having had and worked with a few of YOUR stocks its a shame it turned out the way it has, you had a very good product....
Click to expand...

I'll will certainly agree with that. I have one that I won't part with, and have used many on other people's rifles. The quality was the same on all of them. Great!
 
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