Thursday, March 25, 2010

Rib Fest!

Time to add a rib! Job one is to loosen the previous rib. The mold is waxed but some residue always sticks things together. I wiggle my palette knife to break things free. If I didn't, I wouldn't be able to remove the bowl without damage.
The lute I'm working on is modeled after an instrument from the shop of Paduan maker Wendilio Venere, 1592. It currently resides in the Accademia Filarmonica in Bologna.

I've scribed a line at a known distance from the bottom of the lute that corresponds with the maximum diameter of the bowl. This keeps the figure on the sequence-sawn ribs aligned, which in this case is some nice bird's-eye maple.
Fitting ribs is a bit of a trick. They are only 1.5mm thick, and the form twists a bit - it's not like an orange segment! So I'm bending things in an irregular curve through three axes.
Some modern lutes are made truly hemispherical in cross section, which would make things easier. The makers of old did not do this! They shaped the volume of air contained within the bowl to accentuate certain sound qualities, and so must I.

Bending takes place with this electrically heated iron. The ancients would have used a rod heated in a charcoal brazier. Carbon monoxide poisoning aside, it's nice to be able to control the degree of heat. Bending is a slow-and steady affair with frequent checks against the mold. Things have to be pretty accurate as any deviation makes achieving the proper bevel angle difficult.

Here's my trusty hand plane fitted upside-down in my planing board. Normally I'd have both hands supporting the rib as I take sweeping cuts from the widest point down to the smallest. The plane blade is set slightly askew to give me a choice of light, medium or heavy cuts. Wow. The angle on this shot makes my thumb look freakishly long.

When there's a large volume of material to remove, such as here at the very tip I'll use my block plane set to take a course shaving. I do need to be careful though, as grain in this bird's-eye is so convoluted that it tends to chip out something fierce, even when going with the grain.

Getting closer. When the joint fits tightly along it's length with only light finger pressure, I transfer a series of measurements from the mould to the rib to gauge the taper on the other side. This will take into account any additional width needed to accommodate the spacer I'm using here. I try to end up with a nice smooth taper that approximates a straight line, as this makes fitting the next rib easier.

Yes. I do go through a lot of masking tape. I apply lots of glue to make certain there's adequate wetting of the joint. Over the neck block area I'm using a clamp and some reinforced packing tape to ensure optimum pressure.

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