Rather than bond in metal, it would be lighter to either make some glass 'angle irons' with flanges on each side and then bond them to the existing flat area, or place a piece of light foam or wood on the area that you want to stiffen and then glass over it. The resulting channel sections are light and strong.

Any weight you add will then need to be supported, so you get into a downward spiral and end up at an SUV.

art

 

thaddeus, are you trying to make a male or female mold? or are you making things seperately? The problem with using wood for a male mold (wood goes on inside... insert beavis and butthead u huh huh huh) is that there is no way to get the mold out unless you are just covering one side of it. with polystyrene insulation material (blue styrofoam), you can melt it out of the inside of your fiberglass one the resin sets using some solvent.... i think acetone or MEK or something.

i've heard of people using plaster as a female mold for small things... the problem with making a large mold is that the plaster is very heavy and not able to support its own weight in any complicated shape, and tends to break when you try to sand it. however, i think that wax based release agents will work with plaster... if you want to be sure (and you can keep wrinkles out) a layer of vacuum bag material then a layer of release cloth is the ultimate in ease of mold removal. of course it is also expensive.

i was looking at my hatch this morning before i left for work trying to figure out what you were going to do, and all i came up with is that you must have mad ***** to even try this... good luck.

 

My plan:

(1) Build a male form from wood. It will be a 90% functional version of the finished article. (Shape must be draftable)

(2) Build female mold in PP on top of male form. It will never leave the floor, so strength is not a concern. I may tweak this mold with shapes that are not draftable at this point.

(3) place resin/glass in PP female form. When cured, break plaster mold and discard same.

(4) Finish the surface, add hardware, paint and mount to car.

This is the method I've used in building molds for pouring bronze, except of course in step 2 I use sand mold bonded with alkyd resin.

I am still in step 1. Sigh.

Thaddeus

 

Thaddeus,

I agree that the rear glass should not be inset. In the late 60's Mopar campaigned a Charger("General Lee" body type) in the NASCAR stock car series. They found through wind tunnel testing that the inset glass created a low pressure area and thus lift. To remedy this, they pulled the glass out to the edge of the side pillars. Later they went to an even more extreme level, and created the very exotic and successful "Super Bird".

Ford, Chevy and Pontiac who were all light years behind in aerodynamics, cried and got the car banned (a process Porsche engineers consistently have to deal with).

Good luck with your project.