On Aug 22, 2009, at 11:56 AM, G Cousins wrote: > Jeff, > Yes, bows are dry heated to retain shape. Various woods require > various timings. (duh) > Most modern bow mfg. is in well controlled kilns. Traditional > Brazilwood & Pernambuco woods have a substantially different bend > differential time. > Ribs are wetted (steamed) and different methodologies call for > different techniques. (Think hide glue) Time is the essence. > > I have used Roger's suggestion in some of the harpsichord warping > with varied success. Would have to say that I believe much depends > on the age of the key stick receiving the treatment. Guess is that > moisture content of the wood before during and after the might be > the determining factor for success rates. Does anyone have a > detailed analysis? Maybe Andre or the folks from Kluge. > > BTW Love the jig design Alan (?). Have to make me one. > > Gerry Heat helps set the wood in its new shape. But I think moisture is a big factor. If you start with wet wood (which can mean green, unseasoned), you can usually just use heat. If you start with seasoned wood (meaning virtually anything in a piano, from shanks to keys), where the wood has been carefully dried, adding moisture can help, and can be utterly essential for a relatively large degree of twisting or bending. I suggest anybody just do a bit of experimenting. Put a hammershank in a bowl of water for a while - even as short as ten mintues - and see how much more pliant it is. A wet shank can be easily bent into a bow. Clamped in that shape and allowed to dry, it will hold most of that bend. Clamped and heated, it will hold more. Try to do the same with a dry shank. Use all the heat you want. I think you'll find there is an enormous difference. Try the same with a piece of 1x 2, in a bucket of water. Bow it, twist it. In dry periods here in NM, I find it helps to wipe all the shanks with a wet rag before doing a hammer-squaring job (twisting shanks to get the hammers set at the correct angle). Applying heat alone it takes forever to get the shank to move, Adding moisture speeds it up. If you already have high humidity, your results will probably vary, since your wood's moisture content will already be relatively high. Basket makers, who are bending strips of wood into tight weaves and odd shapes, soak their wood in water until they start working with it. The wood holds its new shape fine (of course, it is held there in part, but if the basket breaks apart, the pieces retain their curves). Trying to do the same with dry wood, you would find it would all split and break. I don't know the science (I've read some, but it didn't stick), but I do know it works. When it comes to keys, it is a question of being able to twist or bend the wood far enough to get it to stay where you want it. I'm sure all of us have experienced broken keys trying to do this. They almost always break at the balance hole (occasionally along an angled grain). So immobilizing the center of the key is the first step. Water then makes the key pliant enough to get it bent into the desired shape. Heat, and drying it, sets the wood and keeps it there. Regards, Fred Sturm University of New Mexico fssturm at unm.edu -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/caut.php/attachments/20090822/95793395/attachment-0001.htm>
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