Making a master from Balsa wood.

[Loach Driver]

I have been working on a balsa wood master for a set of fixed floats for a helicopter model. Because of the shape of the real float, I have had to make this master from two pieces of balsa wood. So far things have gone well. My plan is to finish the master and then have resin copies made (though I won't be doing this myself). I am looking for some advice on final preparation before handing the master over.

1. First, what glue is best for joining the two halfs of the master together; wood glue or superglue? The master will require more sanding when the two halves come together so a strong joint is required.

2. Do I need to do anything to the surface of the wood to make sure it is smooth for reproduction in resin? Will a gentle sanding with fine sand paper be OK?

3. Can any blemishes be repaired with Squadron putty?

Any help and advice will be gratefully received. Thanks.

LD.

[72linerlover]

Hi, LD

1.Though dimensions play an important role (and I can’t figure out how they are), my advice would be: proper glue and putty for each object. Balsa wood is well glued with white vinyl glue or cellulose glue (UHU Hart) or Titebond (these names in Italy; don’t know in your Country). Cyano works too, but you may run the risk of a not uniform joint because balsa soak up it and you don’t know where more and where less.

2.-3.If you are satisfied with the general shape, seal it all with a wood sealer: all work well. Lay it down in several light coats and sand.

Only now you can prime it and then correct eventually blemishes with a normal modeling putty. Because of previous sealing, you may also wet send.

At this stage you have in your hands something that looks like a primed kit plastic part. So you are golden.

Silicone Rubber Mould suggestion: The last prime on the master should be not polished. This helps a lot the release and avoid surface micro bubbles both in the mould and in the cast parts

Euge

[Loach Driver]

Euge, Thanks for the advice.

LD.

[Cap'n Wannabe]

Hi LD..

I'd use wood glue or aliphatic resin to join the two halves together. You won't need much if you use a decent clamping pressure to hold the two halves together, and the joint will be very strong. If you are joining at the end grain, you'll need to seal it first - a good technique for this is to smear whatever glue you're using on the end and allow to dry, then glue and clamp as per usual. Make sure you allow it to dry for 24 hours while being clamped.

Balsa generally needs to be filled to completely remove the grain's texture - there are plenty of suitable wood fillers - but make sure you get one with low shrinkage. You can use a wet finger to work it into the grain, then sand afterwards.

Eugene offers some good advice regarding finishing the master..

[Joseph Osborn]

Balsa is really soft so you need to make sure you have a durable surface to prevent little dings and nicks. I like to seal wood with a coat or two of super-thin super glue. It sands easily to a smooth surface and will seal the grain for silicone molding.

[chukw]

I've scratchbuilt a ton of free flight rubber scale models- and used Ref Devil spackle as filler. Mix a litlle with water until it's like thick melted ice cream, then brush on with an old brush- I used an old solder flux brush! it'll clog the wood pores like nobody's business and sand perfectly smooth. I'd seal it with Thompson's Acrylic deck sealer, but any clear coat will do. Two-part epoxy used for fiberglassing would give you a strong, dent-resistant finish. Good luck!

chuk