Jonathan
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Registered: 7-27-2004
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Shaping the ribs/staves
I'm working on my fifth oud bowl, and I guess it's time to put this question out there.
All the ribs/staves (with the exception of the outer two) are, theoretically, the same size and shape, right? Is it possible to cut them all ahead of
time, to the exact same shape, and then, with the possibility of some minor touches, fit them together?
I know it might seem impractical--good in theory, but not in real life. My brother, an amateur wood worker, has been watching me build these ouds,
and with every oud asks me this same question. In the past, I've just smiled and condescendingly told him it wouldn't work. But now, I'm starting to
wonder.
Stack 21 blanks (or 19, or whatever), cut them all at the same time, and then bend and fit.
Any thoughts?
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Dr. Oud
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I've done this myself, but you must leave at least 1/4 inch/6mm extra width at each end. As the back is built up, minor variations in the cuve and
plane of the edge of the mounted rib will require some trimming to fit the next rib. If you don't have enough material to make the trim and make the
open edge flat, the rib edge plane will begin to twist. The twist will accumulate and the top ribs will have a sharper radius at the apex, causing
the shape to approach a more triangular shape. I don't think it saves that much time over tracing the edge on a square rib blank, then cutting the
outer edge after the mating edge fits.
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Jameel
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Theoretically you're right Jonathan. This is of course assuming your mould is completely circular. Once you depart from this (my current mould isn't
circular at all) each subsequent pair of ribs is different. One idea I've thought about is to design a mould with a CAD program, then carve the solid
mould with CNC equipment to build the oud on. You could then use the CNC to carve a wedge template (it looks like an orange section or lemon wedge)
for each rib (and a mirror image for each, since the matching rib on the other side of the mould is identical, just in reverse). Bend your ribs to
match the mould (if you wanted to get real automated, you could build a dedicated bender for each rib template!), leaving them a bit oversize. Fix the
rib to the template and using a laminate trimmer with a flush-cutting bit, with the router on the flat of the rib, trim both edges. You could also
just plane the edges flush to the template, and that would actually be safer and more accurate. Theoretically you should be able to produce these ribs
very quickly and they should fit on the mould and to each other very accurately, leaving almost no fine fitting. Of course, this is just a theory for
producing bowls quickly. The templates and jigs and such would have to be darned precise to work though without handwork. There's a 99.9% chance I'll
never try this idea! 
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Jonathan
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Thanks guys. A lot.
I'm really just trying to get these ribs as close to the same size as possible. I've genereally been using contrasting wood, which makes any slight
discrepancy more apparent. The purfling between the ribs adds to this even further.
I appreciate the input.
I may end up switching over to one of those solid molds--I think Kyvelos uses this. I have no idea how to make one. Somehow, though, I think it
would really help me make each rib as close to identical as possible, because I would be able to monitor how it conforms to the mold along the entire
length of the stave.
Again, thanks!
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jdowning
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I know of one luthier that has used Jameel's suggestion of an "orange wedge" template for building lute bowls of semicircular cross section (although
few, if any, surviving lute bowls of the 16th C and 17th C are semicircular in section - being either flattened or proportionally deeper in section).
The procedure for making and using the template is described in The Lute Society Booklet No 4 "Lute Construction" by Philip Macleod-Coupe. The
template is used - as Jameel suggests, by clamping each bend rib blank to the template and then planing away the surplus material from the edges. One
way to make this kind of template would be to cut two body profiles in thin plywood and glue in 'V' shaped wedges, cut on a bandsaw to the exact angle
required (e.g. 12 degrees in the case of a 15 rib bowl) - the wedges filling the gap between the plywood profiles. The outer face of the template
would then be shaped to the required finished profile by planing and sanding.
Many years ago - when experimenting with lute bowls made of carbon fibre reinforced fibreglass - I made the bowl master mold from 'plaster of paris',
built up from individual "orange wedge" sections glued together and then finally finished, sealed and waxed. A female fibreglass mold was then made
from the master and this was used to make the lute bowls. I mention this because some luthiers use a solid mold made from 'low expansion foam'
(polyurethane?) - available from hardware stores for gap filling insulation in buildings. This type of foam mold would be cast in such a fibreglass
mold. Alternatively the mould could be built up from foam wedges glued together.
All of this is a lot of work however!
Making solid molds is not difficult but it is time consuming. My current project (Old Project - New Lute on this forum) uses a solid mold made first
by constructing a bulkhead or 'toast rack' style of mold, filling the gaps with pine wood and then carving and sanding away the surplus material to
match the profiles of the bulkheads. Alternatively, the mold can be made from blocks of pine glued together and hand carved or - if a semicurcular
section is required - turned on a lathe to the required profile (in which case you will produce two identical molds).
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