I am making a balsa mold so I can make a couple fiberglass parts for my 1/4 scale F4U-5N Corsair and was wondering what the best thing to do to it so I can get the part off of it. I thought about glassing it and then just using mold release after I finish sand the glass covered balsa mold. What do any of you do when you use a balsa mold if you leave it bare?

Thanks,

Gibbs

GIBB i would glass it and paint it with laquer primmer. Then use your mold release. The smoother the better.

one of the best at this is atlanta 60. he has a nice thread ongoing in the composites forum and he posts regularly in the classic pattern forum.

Monokote works great, just wax with a couple of coats of car wax first. Alternatively, if you only need a single part, you can make the plug from foam then glass over that and then remove the foam. Most types of foam can be dissolved with gasoline or you can just chisel the foam out.

FYI - Technically speaking what you are making is a plug. A mold would be the female counterpart to your plug.

I'm with Chad. If you only need 1 off (like the cowl) just carve it from white foam slightly undersize, cover it to protect it from the resin (I use brown paper & PVA (white) glue) glass the outside then remove the foam when cured. Water dissolves the PVA glue.

You will have some filling & sanding to do but for just one part it's the least amount of work. - John

Getting a plug (core) out without damage can be difficult. Use as much draft as possible (tapered sides). If scale shape doesn't allow health draft, consider making the core from two or three pieces. A sandwich with a wedge shaped center sometimes works well; the wedge only contacts resin on the narrow sides; you pull it out and then pull the outter pieces towards the middle and remove (collapsing core). However you do it, make sure you have a good handle on the plug (like threaded rod) and some way to grab the molded part (like a molded flange). be sure to extend the fiber glass/plug far enough so you have material to trim/clean up damage etc. I don't know how big the piece is but balsa is expensive. Higher density foam is more durable (like urethane "Balsafoam"). Another option is (machinists) wax. It machines/carves nicely. Machinists use it to test CNC programs before committing metal. Good luck - post a picture!!

I have used foam before but I need 2 exactly the same for exhaust deflectors on my 1/4 scale F4U-5N Corsair I'm building from scratch using Don Smith's Plans. Here is the mold but it is not done yet The second picture is another F4U-5N Corsair that Graham Buchanan in the UK of Tiger Models is making. You can see the deflector on the side of his fuse.

Gibbs

If it's only a cosmetic bit have you considered vacuum forming them?

Or just carving another one, gluing both on & glassing/filling over the top?

You are half way there already! - John.