Vacuforming Over Balsa Masters

[PBoilermaker]

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Edited January 13, 2009 by PBoilermaker

[Impatient Pete]

You usually need to seal it with something like CA. The issue is the grain in the balsa (alternating soft and hard sections) will come through in a big way with balsa. It really depends on the particular piece of balsa. If it is very soft, you should harden it. If it's a medium or hard balsa, then you may not need to.

Good luck!

Pete

[johnsg]

Sanding sealer will work, but you'll need to apply at least a couple of coats and sand the piece between coats. The first coat will raise the grain in the balsa as it soaks in and makes the surface of the wood swell.

[Bob Perry]

There are sealers other than expensive and dangerous CA. Try a good quality gloss wood varnish in several well cured coats, sanding between. Apply over the previously applied sanding sealer.

If you can't eliminate grain that way, you can defeat it by vacforming once. Leave the first vacform on the master and vacform over that.

[ross blackford]

Hi PBoilermaker,

How thick is the plastic you want to use for the final pieces? If it's fairly thick, then as Impatient Pete said you may be able to get away with using a medium or hard piece of balsa without any filling or sanding. The thickness of the plastic may well take up the grain without it showing on the outside.

Could you make your master out of a fine grained hard wood instead? You should still be able to produce the subtle shapes you want from such a wood and then use thick plastic for your shaped part. A piece of bass wood should be good for such purposes. I want to eventually get into scratchbuilding some of the more esoteric types that no manufacturer will ever think about doing and about 12 months ago I bought a piece of Tasmanian bass about 20mm thick, 100 mm wide and about a metre long from a timber yard with this in mind when I eventually get to it. This is the type of wood the yard recommended for this purpose.

You could make a small master first and try the various techniques until you find the one that best suits your need.

Ross.

[chukw]

In my Free Flight Rubber Power Scale says, I used Red Devil spackle to seal and fill balsa in 1 easy step. Use a cheap flux brush a to apply a creamy mix of spackle and water. It dries overnight and completely clogs the grain. Sand smooth and brush on a coat of gloss clear coat- I used Thompson,s acrylic deck sealer, but any clear coat will do. Result- smooth, grain-free balsa- light enough for rubber power, but certainly strong enough for vacuforming.. Let me know how this works for you and cheers!

chuk

[PBoilermaker]

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Edited January 13, 2009 by PBoilermaker

[majortomski]

I've molded a gondola for an RC blimp, pulling it over a balsa wood plug that had 10 coats of polyurathane varnish. Finished piece measured 23 x 14 x 12. This was done on a professional vac machine and 0.040 thick styrene.

YOU NEED a good release agent to get the plastic off the mold. And being able to pump air into the vacuum chamber to pop the plastic off the mold helps.

T