I am not too sure about your opinion! Wood has both advantages and disdvantages compared to metal. However wear can be pretty ggod. Consider wooden clocks; these can run decades long, twenty-four hours per day. There have also been quite heavy machines employing wooden gears, with great success. Correctly dimensioned and constructed they should work just fine in an all-wood camera! (I think wind mils have used wooden gears in grainery mills and I believe I have read about wooden gears in old bridges.)
As for dimesional stability, wooden pendulum rods yield better time-keeping than SIMPLE metal pendulum rods unless you go to an exotic metal like Invar. This is because wood exhibits a low thermal expansion coefficient compared to metal and the precision of time-keeping depends mostly on stability of the length of the pendulum (Unfortunately, wood has a considerably worse stability perpendicular to the direction of the grain.) In reality, this is almost certainly all academic at the level of the stability of wood in either direction in this application . Wood is good enough! What I would consider is the strength issue. In some directions wood compares favorably with steel on a weight to strength basis; of course, the dimension of the wood must be greater because its density is lower and the parts of an all wooden clock will probably be somewhat larger than metal conterparts. I would consider the kind of wood somewhat carefully. My best guess is a strong yet fine-grained type would be best. Maybe birch or maple are good and there is high quality plywood made from either one or the other of these available commercially. Perhaps better would be a home-made, multi-ply rack. For example, if I were trying it I would select a good wood which can be bought as veneer. I would glue 7 layers with the center layer having its grain along the long dimension of the rack.Then on each side of this there would be a layer with the grain tilted 20 degrees from being perpendicular to the center layer. Then another pair of layers with grain along the long direction followed by a pair of layers with the grain tilted 20 degrees in the opposite direction from perpendicular. Maybe cap this all off with even two more layers along the long axis if the package has not become too thick. For the pinion, my first guess would be a lantern pinion with plywood end caps. I would try to impregnate the wood well in order to improve its durability and appearance. There may be better layouts for the layers than what I propose and I would be pleased to read about them here! Bob -----Urspr�ngliche Nachricht----- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Auftrag von Bob Fowler Gesendet: Donnerstag, 10. Juni 2004 03:58 An: E-mail discussion about homemade cameras Betreff: Re: [Cameramakers] racks and pinions --- James Mitchell <[EMAIL PROTECTED]> wrote: > Hello! > > I'm designing a camera made solely from wood, no > screws, bolts, or anything else (the lens, > film-holders and bellows being the three exceptions > to > the all-wood criterion). To this end, I'm thinking > on > the focussing mechanism. Simple friction might be > enough to maintain a given focus (it'll be a large > camera), but I'm wondering if a rack & pinion might > be > better. Has anyone on this list ever cut gears from > wood before? Any advice on the matter would be > greatly appreciated. > > thanks, > > James IMO, a wood rack and pinion would be a bad idea. The wood just won't wear as well as metal. Wood is also not very dimensionally stable and I would think that changes in humidity will cause all sorts of problems... ===== Bob Fowler [EMAIL PROTECTED] __________________________________ Do you Yahoo!? Friends. Fun. Try the all-new Yahoo! Messenger. http://messenger.yahoo.com/ _______________________________________________ Cameramakers mailing list [EMAIL PROTECTED] http://rosebud.opusis.com/mailman/listinfo/cameramakers _______________________________________________ Cameramakers mailing list [EMAIL PROTECTED] http://rosebud.opusis.com/mailman/listinfo/cameramakers
