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View Full Version : Using involute gear cutters in wood



keelan
12-18-2009, 03:38 PM
This is mostly a mental excercise; I scratched out a drawing for a jig to generate involute gear tooth profiles for wooden gears (I am aware of Matthias Wandel's stuff on woodgears.ca; but I don't like scroll-sawing out gears). The design would require what appears to be a non-existent router bit with a profile of a rack tooth. An alternative would be to use a #1 involute cutter mill, and to adapt it to cut wood. Given that the cutting edges are all wrong for working in wood, what cutter life and quality of 'finish' would I get working in something like baltic birch plywood?

Mark Hockett
12-18-2009, 03:51 PM
I made all the gears for wooden gear clock for a friend using involute cutters. I sandwiched the gear blanks between some sacrificial wood to prevent tear out and it worked great.

DR
12-18-2009, 05:03 PM
Provided the blank is held rigidly, wood cutters work okay in a mill. Even with the relatively low cutting speeds of typical mills and wrong cutter geometry.

kf2qd
12-18-2009, 05:28 PM
Because of the light cutting forces you could cut a gear in wood using a straight router bit. It takes multiple passes to cut cut all the non-tooth shaped particles, but it requires only a straight router bit small enough to fit down the tooth and a decent indexer. Forces are light so work holding doesn't need to be elaborate...

After all - a curve is just a sequence of sufficiently close straight lines...

waumbek
12-19-2009, 08:32 AM
I'm working on an orrery with wooden gears and plan to laminate a number of .0625 veneers together with epoxy (the grain of each veneer rotated 30 degrees of so) and then sandwich the blank between sacrificial pieces for cutting as mentioned. The composite material will look just like wood but might actually last. Only other way to make decent wooden gears IMHO would be to glue up pie shaped blanks so none of the teeth have short grain.

cheers, Charles Morrill

fasto
12-19-2009, 01:41 PM
I made a toy for my nephew last Christmas with a bunch of wooden gears that could be meshed & compounded and so on. I took a couple pix:
Cutting the gears on the horizontal mill.
http://i451.photobucket.com/albums/qq232/fasto_tt/Gears/th_gears2.jpg (http://s451.photobucket.com/albums/qq232/fasto_tt/Gears/?action=view&current=gears2.jpg)
Video:
http://i451.photobucket.com/albums/qq232/fasto_tt/Gears/th_MakeWoodenGearSm.jpg (http://s451.photobucket.com/albums/qq232/fasto_tt/Gears/?action=view&current=MakeWoodenGearSm.flv)
Finished gears, still on the arbor
http://i451.photobucket.com/albums/qq232/fasto_tt/Gears/th_gears3.jpg (http://s451.photobucket.com/albums/qq232/fasto_tt/Gears/?action=view&current=gears3.jpg)
Pair of 20-tooth gears. The gears are 8DP, 14.5PA.
http://i451.photobucket.com/albums/qq232/fasto_tt/Gears/th_gears4.jpg (http://s451.photobucket.com/albums/qq232/fasto_tt/Gears/?action=view&current=gears4.jpg)
I used particleboard because it was inexpensive and I thought it'd hold up well. It wasn't the best choice because they really skimp on the glue in it now. I ended up "painting" the gears with a thin 2-part epoxy to keep them from crumbling.