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I've just started making the side molds and I was planning on making them with a layer of 10mm MDF top and bottom, separated by scrap pine blocks. All the molds I've seen on here have been solid MDF or ply. Will my method be stiff enough? I'm going to bend the sides with a bending iron, so I'm guessing there won't be too much pressure on the mold - just holding them in place until they're set. I've cut the molds about 3 inches wide.

(BTW, expect lots of questions in the near future - I have finally started building!! )

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"I am always doing that which I cannot do, in order that I may learn how to do it."
Pablo Picasso

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I'm going to say that you will be fine but interested in hearing other replies. Seems to me that a simple framework like that ought to work just fine and even make the mold a bit lighter and easier to handle.

That is exactly what I do except that I use plywood for top and bottom to keep the weight down even more. Before gluing in the pine blocks, I trace the curve of the body onto them and shape them on a spindle sander. This gives more solid support to the sides. I also place a few pine blocks on the form further away from the body to provide additional rigidity.

I now even make my bending forms this way, then staple some metal flashing to the form to finish them up.

You can use utility grade fir plywood, I have several guitar molds built from this and they work excellent and are much lighter. Mine are all 4 layers of 3/4 ply as I like the extra support. My dreadnought mold was the 1st I did with the cheaper ply and it has been used for 5 guitars and stood up well.

Here is a shot of my 000 12 fret mold


Fred

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Fred Tellier
http://www.fetellierguitars.com
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Here's the starting array of molds and templates for my latest build, which is a baritone using my own "odalisque" shape with Jumbo dimensions. My molds are made from either five plies of 1/2" or 3 layers of 3/4" Baltic birch. They've evolved to this point of not needing the perpendicular turnbuckle between the blocks, which I always found to be a huge hassle. I also make blocks that screw onto the ends of each side, that effectively become cauls for gluing in the blocks, and also takes the weight of the mold off the very fragile rims before joining the plates. I also like that they keep the sides registered to a sort of datum, in case you want to take out the rim assembly for example. It's easy to relocate.

You can also see the side bender form I made from the drops and some steel rod. I also make a dedicated waist caul for each shape, along with side templates and bracing templates I draw out in Rhino.

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Mountain Song Guitars www.mountainsongguitars.com