Macassar Ebony enigma

[Ron Daves]

I've been making a concert uke with (I hope) Macassar Ebony back and sides. I've bent up two sides of Mac Eb using a bending form and heat blanket. One side had a fracture on an edge of the upper bout bend, The second side has a fracture all the way across the tight upper bout bend.
Questions:

1.) I built a sandwich of .010 alum. slat/heating blanket/timber wrapped in damp paper towels and foil/another slat. Waited for blanket to = 300 and then bent waist, lower bout, upper bout. Even at 300 degrees, there seemed to be a bit of resistance when I bet the upper bout.
Why the cracks?
2.) The fracture on the upper bout doesn't go all the way through and I'm wondering if I can use some HHG and properly curved cawls and clamps to glue down the fracture, then do some careful sanding.
3.) Just need a general comment as to whether or not one should try to use Mac Eb on a uke with such a tight curve on the upper bout.

[Michael Lewis]

Your wood probably needs more heat.

Stouter metal sheets will help smoothing out the bends and irregularities at the breaks, I like .015" - .020".. I would approach the breaks with more heat, cluls and clamps to make it conform to the curves smoothly. After the side is cooled you can use hot hide glue to fasten down any lifting fibers or cracks with the same clamping set up but with a sheet of waxed paper between the wood and the outside metal sheet. This will prevent the glue from adhering to the metal. Let it dry 24 hours before removing the clamps, and even then the glue may not have dried thoroughly because of the metal, so handle carefully.

[Mario Proulx]

How thick are the ribs? Was the blanket above or below the ribs?