I am trying to make a Gothic arch greenhouse (The classic Gothic arch is known as the quinto acuto or "pointed fifth").
The arcs are 4/5 of the span. The centres of the arcs are inside the span of the arch.
I have created a jig to make a sample arch. Everything was fine until I removed the arch from the jig. I did not wait at all for the glue to dry thinking the screws would hold the arch. But this was not the case, spring-back action is occurred. In this case spring-back was really high because I did not clamp the wood together properly and wait for the glue to dry. If I try to do again, I think the spring-back will be minimal.
My question is: How can I draw the jig taking into account of spring-back action? I am looking for a rough approximation. It does not have to be a perfect calculation.
My jig:
Spring-back:
