Burlap Epoxy over Foam under Atmosphere
First, make a mold to form the composite. I opted for a one part mold, cut from blue foam. Three blocks of foam, 12″x12″x2″, and Gorilla glue spread on with plastic spreader, sprayed lightly with a mister of distilled water, and clamped with weights. The large block was ready in an hour, and glued to a 14″x14″ sheet of OSB for machining.
The mesh file was made in Rhinoceros, and is a block with a paraboloid removed. I imported that into PartWorks3D and generated rough and finish cut paths. I used a 1/2″ long end mill for both the rough and finish cuts. The finish cut was made twice, at 45° and 135°. The surface finish was better than the burlap.
Zeroing the machine made it evident that the vacuum attachment would not clear the part. I removed it, and used a shop vac to pick up much of the chaff as it was made. Lots of vacuuming during pauses, and after the machining to clean up the blueness.
I lay the burlap over the model, made four radial cuts, and marked the darts. I then cut out six pieces of burlap to match. Using Rhino to cut and flatten the mesh, to make a pattern for the burlap: a good idea.
The finished foam model, on board, was wrapped in plastic and sprayed with release agent. Once the epoxy came out, the camera went away, so the mixing of the 24 hour cure epoxy, and pouring and spreading and laying on of layers went quickly and cleanly. Gloves changed three times in the process.
The soaker and breather layer went on, after spray release and rolling punctures. Into the garment bag went the whole assembly, and after a little extra breather layer for the valve, I pulled a vacuum with the HEPA vacuum cleaner. Success. That was easy. Now I’ll put it up on the shelf, *bump* ~sssssssss…
Aw. The board edge cut the bag when I bumped it. The lay up had already splorched the inside of the bag, so I cut the valve and seal off the compromised bag, extended the breather, and placed the whole thing inside another garment vacuum bag, and pulled a vacuum. Success. Super careful now, just fold up the zipper seal ~sssssss. The zipper seal is very sensitive to being moved. Reseal. Re-vacuum. Gently store and back away slowly.
A detail of the burlap epoxy plastic.
After 24 hours, I opened the bag and removed the 
cured assembly.
Out popped the shape in burlap epoxy. A little clean up with the band saw, and it’s still a shape. What can I do with this shape? Turn aluminum foil into paraboloids by pressing between the foam and the shell.
