Official Luthiers Forum!

I am in the process of building lots of jigs and tools. All are from paid for plans. What surprises me is the use of MDF. Why would I use this material for anything except for cost? I think it and particle board make great flat surfaces (benchtops, etc) but for use in shop built machines? Anybody else feel that subing cabinet grade plywood is a better option? Is cost the sole driver here?

Mike

When I was with Fender we used Finnform. It is a phenolic surfaced baltic birch sheet . I also like a solid phenolic and paper lam like Mapletex for stable jigs.
Hope that helps , good luck

_________________
How long is that in luthyears?

I think cost will make you choose. MDF is really stable but it doesn't hold screws very well AND you have to pre-drill the holes if you are using screws. One of the things I started doing with it was to use 1 inch thick MDF (moved away from 3/4) and started gluing and brad nailing with 2 inch brads in an x pattern. If you don't mind the little nubs the brads leave you are good to go. Keep in mind I am here in Florida...and the humidity has been in the 70's and up since April.

When cost is no cosideration, or can't be, I run down to Florida Southern and buy sheets of Baltic Birch.

_________________
There is no difference between the man that thinks he can....and the man that thinks he cannot.

I like the idea of phenolic surfaced Baltic Birch for fixtures.

Any idea where I could find some of the Finnform?

Tim

It's good enough for most things, and it's cheaper and more importantly flatter than most ply I can find here. For building forms, laminated up and with a lick of paint, it's plenty strong enough. All they do is hold the sides in place while you work, so that's hardly high wear. For bending forms, ditto, and it's flat, easy to shape, the lack of grain means it won't tend to deform weirdly when heated. It's also void free.

For radius dishes, well, cutting through the hardened surface risks some warping, but not as much as cutting through plywood might, and again, solid all the way through, coat of paint, and it's stable. It's also nice and heavy, which is a plus in this context.

I also use it to make initial/master templates, as it shapes quite evenly thanks to the lack of grain. Final templates (routing templates, that is) I make out of phenolic (8mm 'Trespa', which I can usually get from local building site skips for a few bucks. New it costs a fortune). For jigs where there's more strain on the parts (binding jig, for example) I use ply, and tend to have to spend a while sifting until I find a sheet that's flat enough for my liking. My bending form, for example, has a plywood base and MDF forms/shapes.

Mostly, unless you're in a real production setting (even 10 guitars per year is diddly, really), I think it makes sense to select materials that are good enough for the task at hand. Would baltic birch ply and phenolic everything be nicer, perhaps better? Probably. Would it make better instruments? Would it make my work easier? I doubt it.

I use a lot of fibercore for jigs. It's MDF with a thin laminate of birch or some other wood on each side. Still have to pre-drill for certain screw placements with butt joints. I really like the stuff.
Terry

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

I've always preferred baltic birch or equal quality plywood for jig tools and jigs. MDF is a
poor quality choice for durability or quality. HDF is a better choice but is not as readily available.
It hold screws much better and doesn't fall apart nearly as quickly or easily.

Regards,
Kevin Gallagher/Omega Guitars

Never seen HDF around here (Huntsville, AL).
I don't know what it is, but I have a serious mental bias against "engineered" materials like MDF, particle board, etc (I'm an engineer). I've seen it dissolve in cabinetry (if something springs a leak). BUT, if MDF can be used with a solid seal, I might rethink. The project in mind is this:

http://plansnow.com/dn3078.html

I am rethinking this design. I do not like the split plattens. Gonna move the roller adjustment to the end. I am adding a motor drive to the conveyor (after the build). I am using printer rubber rollers for the conveyor. (2 for $6 on ebay). If I use MDF, I am gonna use a hardwood binding along each side edge for the pillow block mounting. I will build a base and add a motor. Not sure I care for the see through top (though that is an aesthetic)

So, mdf or not?

Mike

Cabinet grade birch plywood: $42
3/4 MDF: $25

The extra cost seems minimal., but MDF does make sense for drum.

Mike

HDF is simply high density fiberboard as compared to MDF which is medium density fiberboard. It is
engineered differently and is created under much more pressure. It just holds a screw much better and
can bear a much heavier load before flexing or breaking when compared to MDF.

I built a similar drum sander for a friend a few years ago and still preferred high grade plywood for all
of the structure, but used HDF for the drum assembly. He was actually a student who had taken a class
with me for a week. It ended up being an 8 inch diameter drum that takes a 6 inch wide belt. The belt is
held in place by wedges that are driven in by 1/4" - 20 bolts and imbedded threaded inserts. It's worked
well for him for a the past three or four years and he's thickness sanded lots of pieces on it.

We did a dual elevator adjustment that is driven in tandem by a chain and a single knob. Once they are
in sync, a quarter turn provides about .010" of rise that is consistent to within .001" across its 18 inches.

Regards,
Kevin Gallagher/Omega Guitars

Hi Kevin. I cannot find HDF here. I am going to use HQ plywood instead of MDF, but may use MDF for the rollers (for the absolutely flat surface).

I wonder what would be a great hardener for the MDF roller? Nitro? Epoxy? Bondo?

Mike