Official Luthiers Forum!

I've joined my soundboard and done a quick planing job on both sides
just to flatten out a reasonably bad joining job. Anyway, my question is
whether it's absolutely critical that the soundboard be completely flat?

As thin as it is already (though I still have a ways to go to final thickness),
it seems to want to cup a small bit even storing it inside the house and
just leaving it on the dining room table. My estimation is that as long as
it's more or less uniform in thickness, any slight cup won't be a problem
because I'm gluing braces to force its shape anyway.

Another question - I've seen reference to "floppy" and "stiff" to describe
individual soundboards. This one is down to about 0.18" - 0.2", and it
strikes me as what I would describe as "floppy", but I have no frame of
reference. Any way without having held a few soundboards in your hands
whether one falls into the "floppy" or "stiff" category?

Thanks,

Jay

When its resting-you not working on it-clamp it between 2 two foot squares of 3/4 birch ply.Ultimately your bracing will arch it but no sense dealing with a complication-like a nasty twist.Sometimes you can almost watch it curl up -depends on temp and of course, RH.

Mikes advice is sound....when Im working on a top and I have to leave it for a period of time I put a sheet of card on top followed by a sheet of MDF. I then park my plane collection on top to hold the whole lot down.

As for the top being flat....you need to get the show face of the top as flat as possible. Run a straight edge across it to check and dont forget to check from corner to corner as well as side to side.

Just out of interest what's the humidity variation like where you are? It always amazes me to watch how much a thin piece of spruce contorts itself as the humidity changes.

As for floppy versus stiff. I was told by David Freeman to always aim to build "light and stiff".

Cheers Martinkiwigeo38785.8199189815

Humidity here (Memphis) varies widly. I'd guess 25%-99% depending on
the weather this time of year. Usually higher than lower. It does have a
tendency to wreak havoc on wood. I generally keep in-progress
workpieces in the house rather than in the non-climate-controlled shop.
I probably should keep my raw wood in here, too, but there *is* a line I
don't think my wife would be happy about my crossing, and that's getting
close.

Jay,

You don't ever want to leave a top or back resting on a table top, or any flat surface with one side down, and the other side unprotected. It will 'cup'. I was taught to lean them up against a wall or something, so that both sides are exposed. Same after they're braced. Or hang them up somewhere with a clip on the edge.

CrowDuck

_________________
Chris Nielsen
Soquel, CA.

Jay,

We have a wide RH range here in Texas where I live as well. I have installed a temp & RH guage in my shop, went from out of control to a controled environment, pretty cheap, Window Air unit with auto pilot on coming on during the day to keep things more stable. I spent $106.94 at Walmart for the AC unit. I have all my wood stored on wide shelves, B&S an Top sets, fingerboards, headplates, etc. all padded to the shelf, flat weighted to minimize cupping of stock. I do the same as folks are recommending on work in progress, keep it pressed flat.

Mike
White Oak, Texas