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Lost wax carbon fiber molding

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T

Tin Man

Well-Known Member
Jun 27, 2006
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There's been a bit of discussion regarding different ways to work carbon fiber into a useful gun shape, so I thought that I would post this little experimental gun that I did recently. Maybe it will spark some more ideas.

So here are a few progress shots of my first attempt at a gun. It will end up as a small cross section, 52" long enclosed track gun for two bands and a 9/32" or 5/16" shaft. It's intended to be sort of an enclosed track CF euro design, with a butt extension for easy hip loading. I'm trying not to get too carried away with the actual design, while I work the bugs out of the construction process.

I found that the easiest way to cast the wax was to cast it into an oversized brick, let it shrink on top like it wants to, and then cut it to shape. The steel rod in the center reinforces the wax, so it doesn't crack during handling. It will also support the gun later when I'm melting out the wax.



This gun will be about 52" long when done, of which the rear 22" is carbon fiber over teak, so I have a solid core for mounting the trigger mech, handle, etc. The forward 30" is CF around wax, and will be hollow when everything is done. The two pieces are joined with a short CF sleeve.



Next post, getting the wax out . . .
 
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Reactions: trux, Old Man Dave and Spear0Joe
Of course, once the carbon fiber is molded around the wax core, you have to get the wax out. So here's how I finally approached it. I used a $7 piece of stove pipe from Home Depot, and cut a plywood circle to plug each end. The plywood circles also supported the gun so that it wasn't touching the heated stove pipe. A small slot in one of the plywood discs allows melted wax to drain.




And here's the elaborate setup . . .



A thermometer in the uphill end allowed me to keep the temperature at about 160°F. Plenty hot enough to melt the wax, but no danger to the cured carbon fiber or teak inside.



Success!



Next, a few shots of the finished barrel . . .
 
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The finished barrel is still a little long, so that I can trim both the muzzle and butt ends to their final dimensions. It's about 1-7/16" square, with a wall that is just under 1/8" thick, and an enclosed track cut for a 5/16" shaft. My hope is that it will be very maneuverable and easy to swim with, like a euro, but with an 8" butt extension for hip loading. The high mount handle area will get a Neptonics trigger that I modified a little to require a little less height. Nothing fancy, just relocated the spring attachment a littel higher on the trigger.




And strong?

 
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Here's a sketch to illustrate the carbon fiber layut.

I do it in two steps. First I make the layup on the left. I clamp it lightly on all four sides with straight, flat pieces so that the tube wall thickness will be even, and the bottom and sides will be flat and square. There will be some imperfections after this first layup. Sand and fill any high or low spots, and make sure that everything is straight and square. For filler, I use the same West epoxy, doped with colloidal silica as a thickenner to make a paste.
Then make the second lay up on the right, taking time to get the weave as straight as possible. You could also put one of the colored CF / Kevlar sleeves ove the carbon fiber sleeve if you want something other than plain black. After the second lay up cures, just cut the enclosed track the same as you would for a wood gun, which will remove the delrin dummy piece inside the track.
I think next time I may use a 1/4" delrin rod, and two wraps around it, just to give myself a little extra "wiggle" room for cutting the enclosed track.



And here are a couple more pictures for a size comparison. The barrel on the left is a typical 28mm barrel, and the one on the right is a 30mm barrel.



 
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I plugged the end of the barrel with 2" of epoxy mixed with lots of carbon fiber, and then bored it to accept a round muzzle end. That made it easy for me to machine a good, tight tolerance fit . You can see that I stole a page from Don Paul's (and others) guns with the way that I tapered the rear of the band slot.





 
I have the modified Neptonics Reef mech mounted now. The line release slot is cut, but I haven't yet completed the lever or spring resetting mechanism. The aluminum handle is ready for Shapelock, and the forward and rear mortises are cut to fit.
I started working on the Shapelock last night, but that part always takes me a while. Not because it's hard, but because it is so easy to shape that you get addicted to trying to get the fit "perfect"






 
Here's the spring resetting line release. This one is a smaller version of the design that I have been using for a while, but I reduced the max diameter to 1/4", and it is just a bit over 1" long. Because there is little room under the line release, I installed a threaded insert and machine screw, instead of using a normal wood screw.


 
Reactions: Broseidon
Finally, here it is about done, though I may still reshape the handle a bit and still need to check the ballast after I add a reel. I really like the way the bands lay from the angled back of the band slot.
I learned a lot on this build, and some of it will definately show up in future guns. One of the things that I like best about the heavy walled carbon fiber barrel is that it's damn near bullet proof. None of the little dings and scratches that are so hard for me to avoid in the normal construction of a wood gun.

Sorry for the ridiculously long build thread. Hopeully some of it is useful.






 
Reactions: Magpie
Thanks for sharing with the guy's TinMan, their going like having you here.
All the best, Don
 
Reactions: strangelove
That's quality work, thanks for taking the time to post the pics and info :king
 
Thanks for sharing !

That is amazing work

How does one you learn to master carbon fiber like that ?

You should start you own line of guns !
 
Thanks for the kind words, but I'm an amateur at best. You don't expect me to post pictures of the failed attempts do you?

Something tells me that making guns would quickly stop being fun if I were under pressure to get them out for customers. So far, the only guns of mine that don't live at my house are a couple that I have donated as prizes to raise money for worthy causes.
 
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So far, the only guns of mine that don't live at my house are a couple that I have donated as prizes to raise money for worthy causes.Quote: TinMan

Boy is that a under statement. Bravo.
Don
 
Looks great, concerned about it being so lite weight. Kick like a mule.

F AB = -F BA

Jas
 
What makes you think it's lite?

With the Rob Allen horizontal reel (not shown), it's a bit over 5 lbs including a 5/16" shaft, but I'll probably use a 9/32" shaft most of the time.

So I would venture to say that it's a good 30% heavier than a typical euro of similar size and mounting two bands.
 
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Can I ask how many layers of CF did you use to obtain the wall thickness?
 
Foxfish - I used a single layer of heavy biaxial CF sleeve, followed by four layers of 9 oz/yd uni-directional fabric, and topped by a final heavy CF sleeve. It ended up about 0.110" (2.8 mm) thick. The heavy sleeves end up about 0.025" (0.64 mm) thick, and the 9 oz uni ends up about 0.015" (0.4 mm) thick per layer. I played with both tape and heat shrink tubing wrap, neither of which is exceptionally tight. I would expect things to compress a little more if you went with a vacuum bag.

All of the CF sleeves and fabric came from www.sollercomposites.com
 
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Reactions: foxfish
Great - whats that in mm (i will work it out)
Ok thanks, that is quite a lot of coats, what about the final finish, did you have to apply more epoxy as a top coat?
 
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