Bevel Gears

Bevel gears cut on a milling machine are always a compromise. Only a bevel gear cutting machine can cut the proper tooth profile on a bevel gear. That said it is possible to cut a decent working bevel gear on a milling machine. Milling machine made bevel gears are not suitable for high speed use, they are noisy.

The bevel gears you can buy are tapered tooth depth and require a different cutter than for spur gears. These cutters are similar to normal spur gear cutters but make a thinner cut. There is also a parallel tooth depth method of making bevel gears that use a standard spur gear cutter and this type of bevel gear is what "Shopcalc" will calculate.

While it is normal for the shafts of bevel gears to intersect at 90 degrees the intersection angle can be smaller or larger. As the shaft intersection angle gets past 90 degrees and influenced by the pinion to gear teeth ratio there is a tendency for the teeth on the gear to be internal. Trying to cut an internal gear with a milling cutter is not a a good idea.

The calculated face width is a guide and calculated exactly so will give funny sizes. Round the value to a convenient size and enter that in the input box so that OD can be calculated.

Here is the caveat, The number of holes to index to each tooth must be divisible by 4 so not every tooth count is possible. Before doing the bevel gear calculations go to "Dividing head" and select your particular dividing head as the tooth count will be based on your dividing heads hole (index) plates.

The minimum number of teeth on this type of bevel ear is 12 teeth.

Method

assuming that a vertical mill is being used.
1)
 
Angle the dividing head on the milling table to the face angle of the bevel gear you will be cutting.
 
2)
 
Center the gear tooth cutter to a center in the dividing head spindle, by eye if your eyes and judgment are good.
 
3)
 
Adjust you milling table so the cutter just touches the face and zero the dial. Now set your depth of cut to the tooth whole depth by moving the table.
 
4)
 
Some people like to now cut the teeth without any offset as it supposedly gives a better overall finish, skip this step if you want.
 
5)
 
Offsetting for the first finishing cut. Raise the mill spindle by 1/4 of the circular pitch. If you have roughed the teeth in step 4 you must also rotate the dividing head by 1/4 of the holes per index so that the lower side of the roughed tooth rotates toward the cutter. Now cut every tooth, indexing between teeth using the normal number of holes for each index.
 
6) Offsetting for the first second finishing cut. Lower the mill spindle by 1/2 of circular pitch and rotate the dividing head by 1/2 of the holes per index so that the upper side of the tooth rotates toward the cutter. Now cut every tooth, indexing between teeth using the normal number of holes for each index.

When raising or lowering the mill spindle or making the offsets on the dividing head, watch out for backlash or ruin your bevel gear.