Welcome, Andy! Yeah, the Porch is a great place...

you asked about the belly of a bandura:

> The bandura has a very large soundboard that's under a lot of stress.
> Ideally, once strung, the soundboard should be flat.  An experienced
> builder gave me the advice of making the soundboard slightly
> convex (like a
> giant contact lens) so that it straightens out under tension.  On his
> instruments, he makes the center of the soundboard about 2mm higher that
> the edges....not much!  So I figure I can use either my block or #2 to
> carve the convex part, but what about the concave part on the opposite
> side?  (He also springs the underside bracing in addition to the carving)
>
> Woodcraft is selling  a kakuri brand wooden block plane for $24.99. For
> that price, I can experiment with making the sole convex to follow the
> inner curve. Would this be the way to go, or will my regular block plane
> suffice?

A few weeks ago, BugBear gave us some formulas for planing something flat:

>switching symbols, where P is length of plane, B is length of board, S is
set of plane
G = S(B^2/P^2)

Switch this around to solve for the set required to produce the 'sag' you
want:

S = G(P^2/B^2)

Using a #9-1/2 block plane (which has a 6.25" sole length) and assuming that
the belly of the bandura is 2 feet long, to produce a .080" 'sag' (which is
roughly 2 mm) requires a set on your block plane of .005". Not unreasonable!

So the answer is, you should be able to plane the desired hollow with a
standard
block plane. Find some way to set the depth of cut to the desired value (one
way
is to set the plane on a fairly flat surface which won't damage the blade,
then
slide feeler gauges underneath the sole to check the amount of set).

Then plane the piece, but don't start at the end. Start with the sole of the
plane
fully on the piece, and stop planing before the sole leaves the workpiece.
When
the plane stops cutting, you will have achieve the desired hollow.

Hope this helps!

Kelly Cox
Madison, WI