# Vacuum bag vs bolt force (fabricating a carbon fiber wing)

#### lovethepirk

I'm trying to make a near 100% solid carbon fiber wing. I'm vacuum bagging the top half of the wing and the bottom half of the wing separate.
After making sure there is a thin 2mm gap b/w the center of both halves the goal is to put a very strong, thick epoxy between them and clamp the mold together.

I'm wondering if I should use the vacuum bag for this process or use a series of bolts and washers as seen in the attached picture?

<Moderator's note: post edited to include the image. Please do not use external image servers.>

Questions:
1) The surface area of the top side of the mold is 80 sq in and the bottom is 75 sq in. If I draw a vacuum strong enough for 14psi is my total force 155 sq in x 14psi = 2170 lbs?
2) If I use 20 bolts with the a surface area of the washers touching the flange of .38 square inches each and each washer can apply a force to the flange of 300 psi is my
total force on the part theoretically 20 bolts x .38 sq in x 300psi = 2280 lbs?

*The above questions are assuming a near perfectly rigid mold. I'm just trying to see if my math is right.

3) Will only the excess resin seep out of the seems of the parts if I vacuum bag the halves together or will the vacuum cause more resin to escape the mold? I think in theory the vacuum shouldn't cause excess to seep out.

Thanks.

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#### AZFIREBALL

I would think the vacuum method is preferred as it distributes the load evenly over the entire surface; whereas the bolt method would result in concentrated forces at/near the bolt locations only.
I don't think you need to worry about the resin seep-out as it will only need a thin coating to bond the two together. Generally, on a glue line...the thinner the better. (as long as all imperfections are filled).
In fabricating aluminum honey-cone wing sections for the F-86 and F-100 Fighter jets, we used a vacuum bag and applied pressure as well, using an autoclave pressurized to 100 psi (that was back in 1955).
I think your math is OK.

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