![]() ![]() I think you have the approach needed to decide if this will work, but you need to remember that when hobbing the error will accumulate on each revolution of the gear being cut so you need to make some estimate of how many revolutions it will make in the process. The limitation of this technique is the cut teeth hae to be picked up for successive cuts. Modern gearless hobbers are not plagued by such necessities. This problem has been fodder for machine shop apprentice texts in days of yore. ![]() The cosine of the helix angle is used as a constant in the lead/feed formulae. Similarly helical gears can be cut in hobbers without lead differentials. This is called "lead over feed" in my neck of the woods maybe something else in other places. An index set is selected whose error is precisely compensated by the feed gearing thus resulting in a true zero helix spur gear. Assume you need to cut an oddball tooth count. There is a technique in gear hobbing used where index change gears are limited. Since the feed per rev is part of the picture it would have an effect on the amount of change in the helix angle, As revolutions progress index error would linearly accumulate eventually wiping off the hobbed teeth if there was no feed to advance the hob along the work axis. If the lead error is small enough it may be negligible.Įach increment of index error would advance or retard the blank each revolution. If your machine is hard core accurate the effect of index error would be a change in lead angle of the gear teeth. ![]()
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