Namely in a mill where the gear blank is sitting on a mandrel held by some manner of dividing head and the flycutter is sitting at the center height. You'd use it the same way that you would use the gear cutting set. This will tell you all you need to know about cutting gears with fairly simple equipment.įor change gears on the lathe using a flycutter with a single tooth that is ground from some HSS would work just fine and be a lot less work and expense. I strongly recommend that you read a book called 'Gears and Gear Cutting' by a chap called Ivan Law, I think its available on the net. In practice, for lightly loaded low speed gears with reasonable clearances, like change gears, you can. Strictly they are right, the geometry is different. People will tell you that you can't run 14.5 degree and 20 degree gears together. I suspect that Southbend will have used 14.5 degrees. So, the older the machine the more likely the gears are to be 14.5 degree, later ones, 20 degree. A cutter for 14.5 degrees may not, because thats all there was at the time.
A cutter for 20 degree gears will have this fact marked on it. Before that time, the Pressure Angle was 14.5 degrees, much after it tended to become 20 degrees. Lathe change gears tend to be 14,16,18 or 20DP normally.Ī further complication is that the geometry of involute gears changed around the time of WW2, or a few years later.
I wouldn't have any hesitation about cutting a 50T change gear with a No.2 (55-134) cutter. For lightly loaded relatively low speed gears such as lathe change gears, you can stretch these ranges a little without ill effects. You can see that each cutter is an approximation, but it is one which works.
Each cutter will cut a range of teeth, No8 will cut 12 and 13T, No 5 will cut 21-25T, No 2 55T to 134T and No.1 135T to rack (straight). In order to cut the whole range of gear teeth from about 12 T up to a rack, needs 8 cutters. Just to be clear, there are dozens of DP sizes for involute gears ranging from 1 up 100 or more, the lower the number the bigger the gear tooth profile.
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