Mold for fiberglass fuselage

[CaptainObvious]

I've been working for some time on a new design for a UAV, the fuselage is going to be made in fiberglass so I printed it in PLA to make a "plug" to create the molds from it. It's actually four parts (one missing on the photos), so I can experiment with different nose sections later on.
To prepare the surface first I used epoxy putty to fill any large surface irregularities, then several coats of primer and finally acrylic paint, lots of sanding and polishing in between and at then end!
The result looks pretty good, perfect shape and mirror like finish.









If I have the time tonight I will start making the fiberglass molds with it.

[LambdaFF]

This looks great. I'd be interested to know the results if you make the molds from the physical parts instead of the model. What surface finish have you planned for the mold itself ?

[CaptainObvious]

This looks great. I'd be interested to know the results if you make the molds from the physical parts instead of the model. What surface finish have you planned for the mold itself ?

I don't quite understand what you mean by making the molds from the physical parts instead of the model.

The female molds made out of this printed plugs should have the same surface finish as the plugs, to make them first I'm going to apply a layer of hard resin (polyester gel coat) and then add fiberglass and epoxy resin layers on top to build up the mold.

[LambdaFF]

What I mean is that the tool designers I've met usually don't use the models directly but rework them to take into account various engineering issues : retraction, ...

[CaptainObvious]

What I mean is that the tool designers I've met usually don't use the models directly but rework them to take into account various engineering issues : retraction, ...

Well, if there is any changes on the design I can always print new models, also making the fiberglass molds out of this plugs shouldn't damage them, so they can also be modified if necessary.

Tonight I tried to make the first fiberglass mold, for the canopy, and it didn't go well. The gel coat I used needs more catalyst than what the instructions said, so I ended up with the canopy covered in sticky resin that wouldn't harden, to remove it I had to soak it in acetone... which also removed the paint and primer I used to smooth the PLA print, so I have to do the priming, painting and polishing process all over again.

[LambdaFF]

For demoulding in the industry we use silicon sprays (before laying the resin obviously). For moulds that are frequently used we also put teflon (it comes as rolls of adhesive) : expensive but efficient.

[CaptainObvious]

I keep working on this project, now I think I have the process nailed down, I get good (enough) results every time.
Here's some 3D printed plugs (green) used to make fiberglass molds (black) for the wings of the airplane:







The surface finish for the plugs is polyurethane lacquer, it works very well but it's not easy to apply it, it takes five or six very thin coats with an airbrush; if the coat is too thick it develops bubbles.
On the positive side the lacquer gives a very strong, smooth surface, I only need to wax it to keep it from sticking to the fiberglass molds, no PVA release agent necessary.