Posted by BillS on November 28, 2006 at 18:02:50:
In Reply to: Cutting tool for Hypoid Gear posted by samir on November 28, 2006 at 12:33:33:
A hypoid set is a spiral bevel gear set with non-intersecting axes. The amount of displacement measured on a line perpendicular to both gear and pinion axes is called Offset. Machines capable of being set to an offset can cut hypoid members. The other equipment involved is a hypoid tester.
The amount of Offset can affect the spiral angle of each member but the change in spiral angle is applied mostly to the pinion as an increase in angle. The pinion can look similar to a multi-start worm depending on ratio and angle.
Design considerations play a major role in spiral angle selection to keep wear and strength ratings of both members nearly equal. Blank angle dimensions also change with "hypoidiness".
Of course, the summary calculations for a hypoid set take into account the offset so the machine settings would differ from those calculated for an intersecting set with the same pitch, ratio, etc. In other words, you don't simply start with settings for a spiral pair and add offset to the machine.
Differences in load and coast PA aside, the effect on a tooling choice is not so much that the set is hypoid INSTEAD of spiral, but is influenced primarily by the resulting change in spiral angle and blank dimensions (e.g. pinion FW). This affects the effective pitch, and inner and outer point width of the tool especially for the pinion.
I hope someone else wants to share thoughts on this subject. If I've made errors please correct me.
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