How to mold a hood skeleton?

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#1

Hey guys,

I’ve got a question about molding a hood skeleton. The search didn’t bring anything up, but for some reason I remember seeing a hood frame mold. The question -> Should I mold the large “flat area” in the center of the mold (between ribs), or just have 2-3" flanges around the various ribs? I am thinking the first method would make bagging the part easier. What do you guys think? Any pictures would be appreciated.

The reason I’m asking is because I built a hood from my mold of the top skin and used balsa core cut into strips as the ribs. It is a combination of cloth/mat and VER with 3/8" balsa core, all wet layup. It is “reasonably” stiff and comes in weighing around 15-16 pounds (hood is about 21 sq feet). I don’t think I want to build another hood like this again since it was VERY time consuming. I would like to build a skeleton mold and bond the two together once cured. This seems to be the preferred method…

Thanks! :slight_smile:

#2

Your best solution would be to simply use a core material on the actual hood. This will be the lightest, stiffest, and cheapest method.
Second best would be to only make a mold of the perimeter of the hood skeleton. This way you have the hinge and latch locations already, without wasting time and material molding the inner bracing.
BTW, don’t use any FG mat. That’s why you’re hood is so heavy, and it’s doing nearly nothing for the stiffnes.

Good luck!

#3

TET,

Thanks for the reply! I am in agreement with you that for a pin on hood, a full core would be the way to go. I guess that would make bagging necessary in order for the core to conform to the hoods contours. What type of cores (and how thick) are people using for a simple pin on hood consisting of two skins and a core?

For a hinged hood, I like the idea of just molding the perimeter of the skeleton. It sounds like that would be a pain to bag though.

#4

We have done several hoods with just the top using a core. The latches are custom made, and bonded to the underside. For the hinge areas, we have done bolts that go in from the top, with a nice subtle black finish and low heads so they don’t stand out.
Core is generally 1/4" thick, and 2 layers of 8oz carbon on each side. Super strong, super light.

For hoods that need a more streetable look and finish, the skeleton version isn’t too different. The core material still spans most of the hood, up to about 8" from the edges. Bagging the perimeter only is not a problem, and actually easier than doing all the bracing as there are fewer sealing points.

#5

TET, thanks again!

What do you use for cores? I have only used end grain balsa in the past and that doesn’t conform very well to compound curves. Honeycomb seems to be too $$$. Any other options? Vinyl? ??

#6

PUR foam strips…