I have sketched out ( rather poorly) a possible process using plywood as the core with GF skins for strength. It is designed to be within the scope of an amateur and require no expensive tooling or moulds.
Basically most monocoques have a series of boxes which could be made in GF/plywood core. A typical two-seater , mid - engined car will have five chassis boxes with four or five lateral bulkheads
The process is to make each box as a separate plywood box using fillets at the corners and with access holes at each end. The box is made " dry" i.e no GF so any errors etc. only result in wasting the plywood. Once the box is built dry it is laid up with GF on the inside and outside to create a GF/ ply/ GF sandwich. The inner GF is laid through the access holes in each end. The box is turned over during lay up so all GF layering is done horiziontally and downwards.
The cross- section is like this
The process to vacuum bag the box is different to normal. An internal bag (balloon) is put inside the box via one of the access holes , the other is blanked off. Then a second vacuum bag is placed over the whole box on the outside. As shown in the next sketch the inner balloon has a sealed tube with a pressure pipe coming in but also inside the outer vacuum bag which has its own seal with a pipe from a vacuum pump.
The point of this arrangement is to balance the pressure inside and outside the box/GF sandwich. That way no great compressive or expansion load is placed on the box structure but considerable GF laminate consolidation pressure can be used. In a perfect world one pump would pull air out of the vacuum bag and pump it into the inner pressure balloon. In reality I think two pumps and some simple valves would work.
In this way a series of GF/ plywood core boxes is built up. Then the bulkheads ( metal,honeycomb or GF ) are placed between the boxes with adhesive and bolted together. The bolting is both structural and a means of clamping the joining adhesive.
This gives you a series of single curvature boxes with the laminate thickness and strength tailored exactly to need.
To achieve a double curvature box teh same basic technique is use but with an extra step. A series of temporary formers is inserted in the box before the sides are fitted and stringers are laid along these formers. Then diagonal ply planking is attached to the stringers to give the 3D curve shape. Once this is done the formers are removed before closing the box and laying up the GF as described earlier.
I think this approach could manufacture a GF composite chassis with some 3D curvature with very little specialist equipment and fairly low cost. As no jigs are needed the build time should be kept as quick as posisible.
Anyway there is the idea for critiquing here
Edited by mariner, 05 March 2012 - 00:42.