fibreglass and metal

[phantom]

My knee replacement operation has been put off, so I'm starting my C-cab build early.....for the body I plan to mock up a steel skeleton using 1" x 1" rhs then covering that with the thinnest plywood I can find, when I have the right shape I will fibreglass over it. I know there is a different expansion rate between the three materials and fibreglass dirrect to metal on seen areas is a no no, because of the shrinkage difference between the two, but I think the plywood sandwiched between them will stop any shrinkage/expansion marks. Can someone tell me what thickness plywood would have to be used so that there would be no problems....as I said I want to use the thinnest available as there is a number of curves in my plan for the body

 

[Rick]

The thinest you should use is 1/8 Luan it needs to be curf cut to bend around corners.I did a Choppers Mag.Mailbox trike using luan its hard to do but it does work.Why dont you try a Roth system he used a chicken wire base with plaster and vermikulite (cant spell)mix then 'glased over it.After he got what he wanted he let it set up then knocked the chicken wire out with the plaster then he had his car.Also consider that anytime you bend plywood there is a resistence and its gonna want to pop back to its origanal shape.The curf cuts have to be almost through the plywood to relieve the stress.Thats just from my experience im not telling you what you should do.Go here and youll see the body i made.
http://www.retrohobby.com/flashback/tricktrikes/mail/mail.htm

 

[LKE]

Are you familiar with PVA ? It is mold release agent. You could build your structure out of wood, metal, foam, paper mache ? whatever is easy for you to work with. Then spray it with pva, lay your glass over it, then pull the stucture back out. Then glass in supports inside. I do small things like this all the time. Dont know why it wouldnt work on something bigger.

Edit: I just re read the original post. I use a lot of poster board for doing odd, and complex shaps, then the pva over as I suggested. Another trick is to pva a piece of 3/4" melamine, and lay up a single payer of 6 oz cloth. then pop it off, and it will be very flexible, and you can use to form your shape also.

 

[phantom]

Thanks guys, I will be using a number of things to achieve the shape i.e. cardboard, plastic ect. the main structure has to be of the rhs metal tubing which is a strengthening requirement, I hoped covering it with the wooden ply would stop any shrinkage problems associated with fibreglass on metal.

 

[RPM]

We have made several glass tops for these Ts. I used steel tube for the frame work. Then covered the area with .032" aluminum sheet, that we used for dragster bodies. This comes with a plastic sheeting on it to protect the aluiminum finish. Leave the plastic sheet on. Also the shiney duct tape worked good to joint the aluminum sheets together. When we got the shape we wanted. We applied some wax to help with the release, just car wax, lots of it. We laid 1 layer of glass over the entire area and let it kick off real good. Then we pulled it all apart and removed the sheets and duct tape. Then put the glass shell back on the frame work and glassed the skin to the frame. Next we did several more layers of glass.

 

[409T]

A lumber yard that supplies cabinet and furniture makers will carry bending plywood which comes in various thicknesses down to I believe 3/16" and will go around some very tight curves. Some yards also carry pre-kerfed 1/4" plywood that bends tightly as well. That being said however, I really like RPM's method.

Jeff

 

[flatheadgary]

i have not tried this but, you might find it useful.
Dyna-Weld Adhesive Filler (BND662): Autobody Store