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- Jan 21, 2015
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- 67
If you want to make an involute gear, you'll need an involute gear cutter. Buy a set, or make them according to the formulas in Ivan Law's Gear and Gear Cutting (Workshop Practice Series #17). Basically make a button cutter and use the distance between centers and infeed to make the profile of the gear cutter.
Law gives the values for making a set of 6 cutters from 17-20 teeth to 135-rack for pressure angle of 20 degrees and a set of 9 cutters from 10-11 teeth to 135-rack for pressure angle of 30 degrees.
I did some math that let me look at what theoretically perfect teeth would look like for every tooth count. Here are my findings:
Law's cutter -------------- Values are actually for
135-rack -------------------- 150 teeth
55-134 --------------------- 94 teeth
26-34 ---------------------- 30 teeth
21-25 --------------------- 25 teeth
17-20 -------------------- 23 teeth
Here are the full results for Pressure Angle of 30*
Law's Cutter ------------- Values are actually for
135-rack -------------------- 135 teeth
55-134 ---------------------- 55 teeth
35-54 ---------------------- 35 teeth
26-34 --------------------- 26 teeth
21-25 ---------------------- 21 teeth
17-20 --------------------- 17 teeth
14-16 ---------------------- 14 teeth
12 & 13 -------------------- 12 teeth
10 & 11 -------------------- 10 teeth
Notice that the 20* values start to deviate from ideal as the tooth count goes down. The bold values above show that as you get down there, you have to cut bigger and bigger relative spaces--creating thinner and thinner teeth forms--so the teeth have enough room to "turn" in the spaces since the diameters become quite small.
Also, Law states the tooth should be 0.48 of the circular pitch while the space should be 0.52 to add a little backlash as clearance. I did enough math to find his chart values do indeed include this adjustment.
I was able to make an entire chart with every tooth count (from 6 to 150) for 20*, 30*, and 14.5*. However, if you want to make custom cutters, you'll have to "slide up" the scale some amount for clearance as Law did for his low numbered gears. I don't know how he picked his actual tooth numbers. Anyone know?
I'll post the charts in one of the forums here if someone tells me which one.
Law gives the values for making a set of 6 cutters from 17-20 teeth to 135-rack for pressure angle of 20 degrees and a set of 9 cutters from 10-11 teeth to 135-rack for pressure angle of 30 degrees.
I did some math that let me look at what theoretically perfect teeth would look like for every tooth count. Here are my findings:
Law's cutter -------------- Values are actually for
135-rack -------------------- 150 teeth
55-134 --------------------- 94 teeth
26-34 ---------------------- 30 teeth
21-25 --------------------- 25 teeth
17-20 -------------------- 23 teeth
Here are the full results for Pressure Angle of 30*
Law's Cutter ------------- Values are actually for
135-rack -------------------- 135 teeth
55-134 ---------------------- 55 teeth
35-54 ---------------------- 35 teeth
26-34 --------------------- 26 teeth
21-25 ---------------------- 21 teeth
17-20 --------------------- 17 teeth
14-16 ---------------------- 14 teeth
12 & 13 -------------------- 12 teeth
10 & 11 -------------------- 10 teeth
Notice that the 20* values start to deviate from ideal as the tooth count goes down. The bold values above show that as you get down there, you have to cut bigger and bigger relative spaces--creating thinner and thinner teeth forms--so the teeth have enough room to "turn" in the spaces since the diameters become quite small.
Also, Law states the tooth should be 0.48 of the circular pitch while the space should be 0.52 to add a little backlash as clearance. I did enough math to find his chart values do indeed include this adjustment.
I was able to make an entire chart with every tooth count (from 6 to 150) for 20*, 30*, and 14.5*. However, if you want to make custom cutters, you'll have to "slide up" the scale some amount for clearance as Law did for his low numbered gears. I don't know how he picked his actual tooth numbers. Anyone know?
I'll post the charts in one of the forums here if someone tells me which one.
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