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Wondering if anyone who's built a guitar per Trevor's book has used a vacuum press (i.e. membrane type) to cap their braces with carbon fiber tow.

I've built one experimental instrument with carbon capped braces which I applied by hand. After using scotch tape to hold the tow together at both ends, I saturated the CF with epoxy, painted some on the brace and then carefully applied it to the brace. There was some trouble with lifting at the ends and such and it seemed like vacuum might help with something like this.

I've never used a press like this and am wondering if anyone's had any success. Seems like it would be difficult to keep the CF where you want it while applying vacuum though which could throw the whole thing out the window.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Hmmm. Not usually a problem. Never had to consider vacuum. I don't tape the ends, either. I'm usually using 198grm 3K tow and West epoxy. Lifting can be a function of trying to bend the CF around too tight a radius when there is basically only surface tension (not sure if that's the correct term) holding it down. Using a different amount of epoxy can help. You may have too much (so the CF floats off) or too little (so the CF doesn't wet out properly and stick). From what you describe, more likely too much. If you have a pic I might be able to give you some better help.....

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

I was using 12k tow split roughly in half with System 3 epoxy. The lifting I had was indeed on a sharp -ish curve at the end of the brace where it let into the side. I checked and I don't have any pics with the CF capping the braces (finished this instrument about 6 months ago). In the attached pic, you can kind of see the CF between the brace and the back (that wasn't much of a problem).

Very possible that I used too much epoxy as this was the first time I was doing it. This was on the back of my kid's instrument and because I was designing as I went, I had some clearance issues and I couldn't make the back braces as tall as I wanted. I figured that was a good excuse to play with the CF capping.

Still seems like vacuum clamping it would allow you to use even less epoxy. In fact, I just found a site that has pre-preg available with a cure temp of just 122˚F (50˚C). http://www.ambercomposites.com/prepreg/ Don't know if it would stick to wood but a little film of some sort of epoxy would probably do it.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Yep, that would be the problem. Looking at your pic, I def wouldn't be able to get a wrap around that shape of step-down. A longer taper and more CF might do the job, or no step and a different way of doing the join with the linings. Any number of ways of designing around it if you aren't designing on the fly!

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

I had the same problem on the step-down on my UTB but all worked well after I stopped, cleaned it off, and eased the transition. I found I got the best results by putting the epoxy on the brace, laying in the dry tow and then kind of "squeegee-ing" the tow with a small wooden tool. When I tried to pre-wet the tow the fibers tended to come apart on me. Definitely a learning curve working with this stuff. Only done it on one guitar though so YMMV.

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Steve Smith
"Music is what feelings sound like"