Official Luthiers Forum!

I notice body modes use a LOT of plywood... and leaves a lot of waste too. So I was wondering why should I use baltic birch for making molds instead of MDF or regular 7 ply construction plywood?

I just picked up some baltic birch plywood... man it's so expensive. Paid about 60 dollars for one sheet 150cm x 76cm, 18mm thickness. I rather not use it if it's not absolutely critical...

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

I've just made a couple from 18 mm Baltic Birch. My first ever moulds even though I've been making for over 30 years!
They are an outside mould, just one layer and only 30 mm wide around the perimeter. Pretty minimalist as moulds go. Very light in weight too. I don't really see the point in using 4 or 5 layers when you can just use one layer or 2 or 3 layers with spacers. Save a lot of material that way.

Regular construction ply here, 3 x 18mm, 50 mm wide sides for outside molds
Birch Ply is way too expensive

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I use big box plywood but with a smooth face - not construction stuff for subfloors, etc. I agree Baltic is too expensive for this application.

_________________
Jim Kirby
kirby@udel.edu

Todd - where do you go for BB? Sources I know of in the Wilmington DE area are way too expensive.

I wish I had bought a bunch of the birch ply from Chile that Home Depot had a couple of years ago. It was nice stuff and cheap too. Maybe they will have it again but I haven't seen any recently.

_________________
Jim Kirby
kirby@udel.edu

3/4" construction grade, lighter but ugly, in my mind I am building a tool not furniture.

Fred

_________________
Fred Tellier
http://www.fetellierguitars.com
Facebook page http://www.facebook.com/pages/FE-Tellier-Guitars/163451547003866

the thing about BB is this: it's outer layer is not a veneer, it's a far more substantial layer of wood which won't easily delaminate...I'd prefer to use BB for the outer layers and cheaper stuff for the interior...

If you are not making a block mold at the same time as you are making an outside form (in which case you are not wasting a whole lot of plywood) you can make the outside form from smaller pieces. I have used scraps of 3/4 inch plywood and staggered the joints to make 3 layer, 2 1/4 inch thick outside forms. Use plenty of glue to stick things together and they are stiff enough.

I just use MDF!

Blocked and lamed dimensional lumber, OSB, MDF, sub flooring, G1S, Baltic...it all depends on your persuasion and your bank account. All will work.

Gee you could even use glued up cardboard boxes for that matter.

_________________
.

Audiences and dispensations on Thursdays ~ by appointment only.


.

Baltic birch is not only expensive in Taiwan but hard to find.... they only sell one type of plywood and it's the crappy type, and a 3x6 sheet still costs about 30 dollars (for the crappy plywood that is)

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

MDF or 1/2" construction grade spruce ply("sheathing") here.... MDF works fine, but is heavier than the spruce ply and as I age, I seek to build lighter molds....

Yes

French Skeleton version. Should save a few coins. I'll chop the bolts later. I've yet to try it but see no reason why it won't work.

I would def save your baltic birch plywood for some other more critical application. It makes wonderful jigs that require a nice stable substrate. And good quality baltic is really a furniture grade plywood that is free of any voids and has a great looking surface veneer (although thick is still considered a veneer). There is nothing wrong with using MDF as a mold, its downfall would be its weight and the fact that it really doesn't like to get wet at all. But the wet issue is easily fixed by applying a finish. I personally would rather use MDF as I think a heavy mold would actually be benificial other than having to lug it around. My other problem with MDF is the dust produced while machining.

+1 grumpy. I have made molds from all types of wood BB , chinese birch ply from homeless depot and MDF , cheapo fir plywood, 2 layers of mdf with cedar spacers from the kinkade book etc etc.

I've yet to try it but see no reason why it won't work.

That'll work to hold the shape, but it won't help prevent "racking"(IE: twisting) of the rim when gluing the top and/or back to the rim, which is one of the most important tasks of a solid mold.

Just make a second pair, and use spacers between the two. It's all I do, now. At thew waist, I'll build-up a solid stack of spacers and using a router bit and top bearing, trim the block flush to the form. This gives me a solid waist area to prevent cracking the ribs when using a spreader.

I won't need to do that Grumpy. The Back Bars are first glued into the Sides with the actual Back plate glued after. That's the Torres method apparently. I've never tried that before but many have. Anyway, no chance of the twist you refer to.