Tuesday, February 17, 2015

Bending iron

The bending iron is an essential piece of a luthier’s kit. My well-loved one, comes from Touchstone Tonewoods and its irregular oval shape will cope with most curves that you’ll encounter.
So, I’ve just completed bending the solid linings for Jonathan’s mandocello. There are 8 separate pieces that are bent and then glued in place to create the instrument’s rim. These linings are made from sapele which bends with relative ease.
On the other hand, I’ve also just bent the sides for Alex’s twin-point mandolin; these are cocobolo and it’s probably one of the trickiest woods you’ll ever work with.
With any sides, you have to plan which way you are going to bend them so that the book-matched grain pattern works out. This is doubly important with my twin-point design, as half-way through the bending process I cut the sides in two (you’ll see what I mean in a moment).
I soak my cocobolo sides for about 30 minutes in water with fabric conditioner added; this can help to make stubborn wood a bit more pliable!
For this particular type of wood the bending iron has to be really hot. In general, as you touch the damp wood against the hot iron, the moisture instantaneously turns to steam,thus making the wood pliable. With cocobolo, its resin boils and comes to the surface and this too makes the wood pliable. I find that cocobolo will not bend until the resin boils. And again, unlike other woods, the resin seems to retain the heat in the wood, so unless you cool it down quickly by quenching it in water, the bend doesn’t stay in place.
Once the sides have been bent they look more like victims of a thermo-nuclear attack rather than the product of the luthiers’ gentle art! You can see the resin’s effect on both the sides and the bending iron…………
In the past, I’ve cleaned up with a cabinet scraper and fine abrasive paper, but it’s much easier (albeit messier!) to use wire wool and meths!
With the sides clean, the supporting blocks for the points can be glued on; but that’s another story!



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