ORIGINAL: acdii
I am going to make a mold off of the cowl that comes in the CG Chipmunk kit. Question I have, should I first cuat apart and assemble the cowl, or should I make the mold off the cowl as it comes in the kit? My thinking is I make the mold off as it sit, then cut it in half and have the two halves for making the actual cowl as one piece.
The way I do cowl molds depends on whether the cowl is flanged around its perimeter for stiffness or is a simple non-flanged part that mates around the fuselage.
If the cowl is simple with minimum compound curves, I make a one piece cavitymold.
If the cowl has a lot of complexity with undercuts like flanged mating to the fuse, a two part mold is simpler to work with in the long run. I install a parting board in the middle of thepart being molded and proceed to cast the two piece mold. I create a flange at the parting board so that the two halves can be re-alligned precisely.
Once the first half is curedI remove the parting board only, prep cowl half that's exposed and the new flange I just created and cast the second half directly onto the first half. I don't separate until the second half has cured. But first I add a series of hardware (blind nuts and screws, usually 8-32) to the flanges, then separate the two halves.
When making the actual part, Each half can be worked independent of the other, casting in all undercuts and any specific complex details. I leave about a 1/2" strip unglassed in the crown where the mold flange is, until I put the two halves together and bolt them securely. ThenI add the last strip of glass while the epoxy is uncured. No need for a taped seam which isn't as strong and adds weight. The whole cowl is cast as single piece in a two part mold without a seam tape section. Strong and light and simpler to separate once cured