Falcate Bracing in Curved Radius?

[Kim Strode]

I am a little confused as to how the Falcate Bracing maintains the correct curved radius when the bracing is not pre-shaped to the curve before being glued down onto the top, unless I've missed something? I understand that the go-bars are forced the bracing into the curve of the radius dish, but I would normally expect the top to spring back if the bracing was not also curved.

Am I correct in surmising that when the epoxy sets, it achieves the correct radius curve because it is all done in the dish together with epoxy and cf rove in the process?

[needsmorecowbel]

Gday Kim, I asked the same question in a thread recently here are the responses:

Dominic: "No, you just press them into the dish and they tend to hold shape apparently. And Trevor mentions it is much easier to get the geometry right if they are flat. I'm about to do my first one so I have to trust in what others tell me. "

Woodrat: "Dom, They just squash in there and stay put when the epoxy is cured....the CF tow cannot stretch so therefore they keep their shape..."

Here's the Original Thread:

viewtopic.php?f=24&t=4150&p=50507&hilit ... ces#p50507

[kiwigeo]

Yep you just whack in the braces after laying up some CF tow with resin and amazingly the top will hold the radius of the dish.

[Kim Strode]

Thank you both for your response.

[weslewis]

I laminate 2 pieces of spruce, .080 to .090 thick.. 3/4 inch wide , lightly radius both sides in the radius dish and then cut in two pieces in half and finish to the correct height...not sure if the radius is necessary but doesn't hurt...

[Trevor Gore]

I just make sure the brace bottoms are square and fresh planed, then stick 'em down. Never a problem. I've tried sanding a radius on, but got a better gap-less fit leaving them square.

[Tj Turner]

That was exactly the same question I was just asking myself, so I ventured over here to poke around.

Looking at the pictures in the book, I still worry that I will be able to get a great bundling with the fiber below the brace. Has anyone had trouble with this, any suggestions to help? I'm probably just being paranoid, as on my conventional builds I spend so long making sure the fit is perfect...

Trevor...I just finished reading the books from cover to cover. Absolutely fantastic.

Thanks!

[DarwinStrings]

Hey TJ. Provided you use just the right amount of epoxy the CF tow gets flattened between the two bits of wood so you have a wood/CF/wood bond which relies on the nature of the epoxy for the bond, not like wood to wood with a wood glue. I paint the epoxy on both bits of wood just enough to wet it without leaving a glossy film of epoxy. Then I lay the CF tow onto oven paper and brush epoxy through it again just enough so that it is wet through without any excess. I use a number 4 pig hair brush (cheap job) and I cut the bristle length in half giving me a short stiff brush (Trevor shows a different technique in the book). I then lay the 3K tow on the soundboard centrally, neatly and accurately between the outline of where the brace goes. Next is to overlay the brace and add pressure with go bars checking that you have the brace very square to the board as you go. I don't get much if any squeeze out and from doing some checks on scraps the bond is sound. I would suggest that if you have never done it before then just do a few joins with scraps first to get a feel, if you get to much squeeze out or slipping of the pieces then you probably have too much epoxy, try again till you are comfy and you don't end up with too much glossy bits of cured epoxy. Try breaking your samples and you will see how tough that epoxy is.

[Tj Turner]

Thanks Jim...that's exactly what I'll do! This will be an adventure!

[kiwigeo]

TJ, do a couple of practise runs on some scrap spruce......youll soon get the hang of how much epoxy to apply and how much CF tow to lay on same. I use cheap small hobby brushes for the job and chuck them after the job. The biggest problem I found was applying to much epoxy and having the CF tow "float" around when the brace is applied.