: How would you go about making a glass copy of a sit on top cockpit?

: is there a forum that specializes in making molds and glass parts?

: I could do stitch and glue i suppose. I even found such a seat for sale
: but after looking at it i'm not sure i will buy it.

There are lots of ways to make a mold that works but much of it is using professional materials and technique. If you are casting off a surface that is pretty much flat with little inclines to worry about then molding plaster is pretty simple. This can be bought in different size buckets or 50 lb bags. You can wall or dam up around the sides using modeling clay and cardboard. More experienced persons can work up a wall but that is all timing. If it is a mostly flat area, grease the surface with Crisco or something similar and don't leave grease ridges, get the excess off or they will show in your cast. Mix the plaster to the consistency of pancake batter with no lumps. Then for a good surface lightly brush on a coat of plaster. Don't brush too hard or you will brush off the parting. Then simply slowly pore on the plaster. You can pat the surface to bounce out bubbles and make a better surface. After the plaster sets, wait until the heat just goes out of it before removing. It isn’t as strong as it will later get but he mold surface next to the seat develops a dampness that helps in the removal of the mold. To strengthen the cast just after pouring you can pat in rope hemp or some similar material if you have it. Actually you could probably just pat in some scrap fiberglass. Just to be extra safe you might put a coat of past wax on before the grease.

John