Erik's Hjørne: BENDING BINDING..... AND BONDING WITH IT

INITIAL PREPARATION

The binding had already been prepared back when I was resawing the bubinga board for the back and sides. Part of it was made into bindings and the back strip/end graft. However, all the saw marks was left on and I had to do a little bit of planing to get rid of them.

The four binding strips was secured to the bench with some doublesided stickytape and planed to a thickness of just under 2mm - about the thickness of the sides. I would have liked to have had them a little thicker, just over 2mm, but this was how they ended up.

BENDING
The four binding strips was taped together to form one flat unit. They were laid as a bookmatch, two bindings facing one way and two the other. This ensured that two were bent one way and two the other.

I taped the ends and the flat bit on each side of the waist leaving all the area that was going to be bend exposed. Initially I had added taped in the middle of each of the bout for support but took them off again as the bending progressed as they hindered the heat to the bindings and wasn't all that crucial to keep the assembly together.

The purfling had one side of the sandwich jointed while the other was left with the sawmarks from the bandsaw. They were tied together the same way as the binding strips, however, their orientation was determined by the jointed and unjointed edge, the idea being that the jointed edge will be the one facing down and glued to the soundbox.

The bending was done pretty much like the sides. I felt I started to get a little more feeling for the relation between the feed rate and pressure and was able to control the bends better with more even bends and less need for correcting overbends.

The trick seemed to be to neat up the wood on the pipe, move it along and bending it while heating up the next segment. If one segment got more heat it would continue to be hot for longer and therefor continue to bend for longer, creating a sharper curve. Developing a sensitivity for this dynamic, appeared to be the key creating smooth flowing curves.

The purflings were subjected to the same treatment. However, they were considerably more plastic, to the point that it was difficult to control them. A slight touch on the bending iron and they seems to get almost gooey. I don't know if it was the glue that caused this willingness when heated up or not but they were indeed very malleable.

When the bending was done I clamped the binding and purflings into the jig I used for the sides and kept them there until they were ready to be glued on. The binding went on the side of the jig and the purflings was clamped onto small shims, the thickness of the sides, that was stuck in between the cauls and the jig, and kept there until they were ready to be glued to the body.

PLANING BINDING STRIPS