Well after a week of failures bending the Florentine bindings I was about ready to pull my hair out. I've had issues bending some stubborn ebony and other highly figured woods but NOTHING as compared to the frustrations I've had bending this Pernambuco. This is only a small sampling of the failed attempts:
I took last weekend off for a much needed break. I turned to an old fashioned sketch pad to put some thoughts down on paper. When you bend wood over a form, hot pipe or any other object of your imagination, the inside of the wood fibers are in compression while the outside of the wood fibers are in tension. This Pernambuco wood ALWAYS fractured on the outside of the bend which was in tension so I imagined I needed more pressure on the outside of the wood. The wood was also becoming very brittle in my previous bending attempts. I had to find a way to add more pressure to the outside of the wood while reducing the heat induced embrittlement in the wood in the heat effected bending zone.
Bending wood over a heating blanket poses some problems because the entire piece of wood is being heated at once, which works well for the majority of woods, but not in my case. I needed a way to control the heat in a smaller and more localized area. Bending wood over a smaller hot pipe allows one to apply heat in a much smaller localized area but its difficult to apply an even and higher force to the outside of the wood. I had my best results bending over a hot pipe but I couldn't apply enough force to the wood. The Pernambuco would get to the yield point and begin to bend and then it would just snap whenever IT decided to.
Finally the light bulb went off and I came up with a design that would allow me to position the wood vertically, apply heat only where I needed the wood to yield during the bend and also allow the rising heat and steam to preheat the wood ahead of my bend, without drying or over heating the wood. This is what I came up with on paper and later built a prototype in the shop Sunday afternoon.
It uses heavy springs at both ends of the stainless steel outer bending slat which provides plenty of outer force on the wood and a constant and controlled downward pressure on the wood fibers during bending. I bent the wood over a smaller silicone heating blanket but the blanket only comes into contact with the wood when its being coaxed around the form. I am happy to report that it worked like a charm on my first beinding attempt.
Don't worry, this is not blood! Pernambuco bleeds color when water is applied to it...
Success! ... FINALLY!
Thanks again to those of you who sent words of encouragement and prayers our way. They were certainly appreciated!