I've got the Keilwerth video on VHS tape and it's very interesting.
I also have a Keilwerth SX90R tenor and alto which Steve Howard has looked at and showed me how not all the tone hole rims are flat. Now, this doesn't particularly bother me as the horns play OK, but it is a definite fact - I can see light when a flat surface is held against some of the tone holes. It seems to be especially the larger tone holes that are not flat.
I think that the Keilwerth video gives a clue as to how there manufacturing process could lead to warping. The tone holes are formed by drawing and then machined flat. Later on, separate rounded rims are fixed to the tone holes by soldering. It seems to me that the act of soldering might lead to warping of the previously flat tone holes, because the body and tone hole chimney is heated and any stresses left in the metal could cause it to move/warp. And I think that this effect would be most pronounced on the bigger tone holes, down on the bell and bow, where the metal thickness is smaller compared with the size of the hole.
There is no further machining to flattening the Keilwerth tone holes after the rims are soldered on.
Manufacture of true 'rolled tone holes' doesn't involve any soldering or heating, so there would be no reason for the tone holes to warp.
What do you think ?
Rhys
))
