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Gluing CF Into X Braces and Cutting X Brace Joint
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10117&t=23633		 Page 1 of 1
Author:  Chris Paulick [ Mon Aug 31, 2009 6:13 am ]
Post subject:  Gluing CF Into X Braces and Cutting X Brace Joint
Author:  Andy Birko [ Mon Aug 31, 2009 8:09 am ]
Post subject:  Re: Gluing CF Into X Braces and Cutting X Brace Joint
Chris,

I like your fixture for holding the pieces in place for glue up - excellent idea. I have a couple of questions on the glue itself though.

I used a spruce/CF combo in my last bandura except the brace was capped instead of sandwiched like yours (I may try the sandwich in the future banduras definitely have an issue with cold creep over the years). I also used PU glue (except I used the brown GG). When I tested to failure, I did get a glue line failure of the CF to wood. Have you tested your system to failure? I'm hoping that it will hold as it's in shear on my top but I still wake up at night sometimes :shock:

When I did it, I sanded the wood and the CF lightly with like 220 or something like that to get a fresh surface.

I'm thinking that probably epoxy would be a better bet for CF to wood but it just seems like such a waste to mix it up for the few drops you need (shamefully, that's why I used the PU glue).
Author:  Chris Paulick [ Mon Aug 31, 2009 1:13 pm ]
Post subject:  Re: Gluing CF Into X Braces and Cutting X Brace Joint
Andy, I haven't done a stress test on it. As that CF is a bit expensive. That was the 4th. piece I glued up. The first was just between the two 2X4s and it moved and is no good. I guess I could test that piece. After that I did the brad thing. And then it was still a little clumsy so I added the dowels for the video. Much nicer as you can see. I put the last two clamps on with the setup sitting on the bench and not on top of the vise. Had to do that to be in frame for the video. What I don't do for you all. :P
But as far as the glue goes it was Mario Poulx who told me to use Poly U glue as he has found it to be the best for this purpose and he has been doing this for some years now. I know you need a good clean joint with good clamping for Poly U glue. I did scrape the spruce with a razor blade and clean the CF. The purpose of the CF isn't for strength in case but more for its memory. I believe Mario said that .030" made it too stiff and that's why it's .022" CF. Although he is using Elmer's Ultimate glue at this time which is their Poly U glue. I used the Gorilla because that's what I found locally and the drying white I thought might be visually better.
Also be carefull with the CF dust. If it gets on you it feels like fiberglass and that can't be good for the lungs.
Mario also suggest saving the Dado blades from dulling as the CF is hard on blades and using a 24 tooth 7-1/4" Diablo blade and nibble the joint.
Author:  Chris Paulick [ Mon Aug 31, 2009 2:00 pm ]
Post subject:  Re: Gluing CF Into X Braces and Cutting X Brace Joint
The first two are broken on the flat and the third not. I don't see it being a problem. It was pretty tuff to break on edge. What do you think? And no runout! :)
That was cut from some of Shane's brace wood billets.
That brace wasn't cleaned up as you can see the white foam squeeze out in the one pic.
Author:  Chris Paulick [ Mon Aug 31, 2009 2:13 pm ]
Post subject:  Re: Gluing CF Into X Braces and Cutting X Brace Joint
I was told to treat the CF Dust much like Asbestos as it's very nasty stuff.
Author:  Andy Birko [ Mon Aug 31, 2009 5:12 pm ]
Post subject:  Re: Gluing CF Into X Braces and Cutting X Brace Joint
Chris Paulick wrote:
What do you think?


That looks pretty darn good and much better than what I experienced. I'm either doing something wrong or the CF I'm using is different enough that the PU glue doesn't work on it.

I capped one brace specifically for ultimate strength because I am height limited in that brace (see pic below). I used strips of CF from [url]http://www.dragonplate.com/ecart/categories.asp?cID=20]here[/url], not the place you used. As I said though, I haven't heard any pops in the night or seen my top collapse yet.

I'd be using the sandwich thing for the same reason you are, to avoid cold creep over the years.
Author:  Darryl Young [ Mon Aug 31, 2009 10:19 pm ]
Post subject:  Re: Gluing CF Into X Braces and Cutting X Brace Joint
Very nice video Chris.

Now can you use a band saw to cut a scallop profile into the braces? Any ideas how low you can go height wise on the brace since you have the added strength of carbon fiber? Seems standard height would be too stiff for good sound.
Author:  Chris Paulick [ Mon Aug 31, 2009 11:07 pm ]
Post subject:  Re: Gluing CF Into X Braces and Cutting X Brace Joint
It's the first time I'm using it but you can cut it with a band saw and a chisel and a plane. It's just hard on tools as it dulls them. How much lower you can go??? As I said it's really not there for strength as it is to keep the braces shape over time.
Author:  Darryl Young [ Tue Sep 01, 2009 12:13 pm ]
Post subject:  Re: Gluing CF Into X Braces and Cutting X Brace Joint
Why you chose to use CF is one issue.......whether or not it adds stiffness is another issue. If it adds stiffness and you don't compensate by lowering the brace height, it will change the sound of the guitar you build compared to how it would sound if you used similar height braces made from all spruce. Am I wrong? If so, what am I missing?

I will guess you will loose bass response if you don't lower the height of the braces compared to what you typically use on an all spruce brace.
Author:  Chris Paulick [ Tue Sep 01, 2009 2:32 pm ]
Post subject:  Re: Gluing CF Into X Braces and Cutting X Brace Joint
You will have to voice each top you do regardless. And I believe stiffness and strength are two different things.
Darryl, if you want to discuss CF in braces then start another discussion as this one is not on that subject. It's a tut on gluing it into the braces and slotting the X braces. I can't answer those questions for you but maybe someone else can. Maybe after I build some with them then I can tell you what I think. Go over to MIMF and post the question as Mario post there and he's the one who has been doing this for years so maybe he'll give you some answers.
Author:  Mitch Johnson [ Sun Sep 06, 2009 6:15 pm ]
Post subject:  Re: Gluing CF Into X Braces and Cutting X Brace Joint
I like the use of a dado and sled for cutting the X-brace...I just hand cut one yesterday, this would have saved me a lot of time had I seen this tutorial a couple days earlier. Why didn't I think of that... idunno . Great video.
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