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Old Nov 10, 2003, 08:24 AM
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Newbury Park, California
Joined Apr 2002
651 Posts
[B]Carbon Fiber/Spruce Spar Cap Construction Questions [/B]

I intend to glue CF and spruce strips to make composite spar caps. The spruce will have a 1/8 x 3/8 inch cross section and the unidirectional CF will be both .007 and .014 x 3/8 inches. Length will be 48 inches. (The purpose is to toughen-up the Mirage I?m gonna build )

How would y?all go about gluing and clamping this lamination?

Glues:
I have had wonderful experience with rubberized CA and could use it. If epoxy would be better, I?d like to know which epoxy to use and would have to practice with it. Would the LHS epoxies do the job, like 30 min or finishing or ---- ? Could I use alaphatic resin? It is tough and flexible. Which of these three choices would last longest? What would you do?

Clamping:
Appying reasonable pressure uniformly to a 48? long strip of spruce with a slippery substance between it and the CF sounds like a tough chore. I have a flat bench and a piece of thick glass 48? long. I should be able to build a flat composite spar.

I can use waxed paper or plastic wrap keep the glue where it belongs. I can make & glue down straight edges onto the glass that are just tall enough to align the CF & spruce and prevent them from sliding laterally. The top of the spruce would then stand slightly proud of the straight edges. How would you clamp this assembly?

This is fun )

Joe
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Old Nov 10, 2003, 08:46 AM
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Hawksnest's Avatar
United States, PA, Perry
Joined Apr 2002
492 Posts
Re: [B]Carbon Fiber/Spruce Spar Cap Construction Questions [/B]

Quote:
Originally posted by Joe Minton
I intend to glue CF and spruce strips to make composite spar caps. The spruce will have a 1/8 x 3/8 inch cross section and the unidirectional CF will be both .007 and .014 x 3/8 inches. Length will be 48 inches. (The purpose is to toughen-up the Mirage I?m gonna build )

How would y?all go about gluing and clamping this lamination?

Glues:
Joe
Joe, I just run a bead of thick CA down the middle of the spruce/bass spar, with the carbon (wash off with alcohol first) full width sheet flat in front of me, and then turn over the spar and carefully align it down one edge of the carbon, pressing all along the spar to keep it in contact until it bonds. Spruce doesn't bond quite as well with CA, as does basswood, so take care to keep it down tightly for five minutes or so until it cures. Then take a new #11 exacto blade and cut down along the spar until it separates from the full width piece, then do another one. If you choose to do epoxy, it will work the same, except I use pieces of flat steel 1" wide to lay on the spar until it's cured, then cut it off next day. I use CA so I don't have to wait overnight for the West bagging epoxy to cure. I would go with .014" carbon top, and .007" or ,014" bottom. Bill G.
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Old Nov 10, 2003, 08:50 AM
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United States, PA, Perry
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Re: Re: [B]Carbon Fiber/Spruce Spar Cap Construction Questions [/B]

[QUOTE]Originally posted by Hawksnest
[B]Joe, I just run a bead of thick CA down the middle of the spruce/bass spar

Forgot to say, when fully cured, hold the spars on edge and sand both carbon side edges so that the spars fit into the rib slots. Use a sanding block lightly, and don't breath the dust.
I dampen wet-or-dry paper to do this, the spars will dry fine. Bill
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