Posted by Bill S. on October 29, 2000 at 14:05:53:
In Reply to: undercut posted by Kevin D on October 26, 2000 at 12:48:19:
I think the potential for undercut produced by a shaper cutter depends on the number of teeth in the workpiece, and whether the OD of the workpiece is enlarged or not. Undercut begins to occur below a certain number of teeth. Undercut can be prevented, within limits, if the OD is enlarged and the cutter is "held out" by the same amount.
Normally, undercut occurs on the smaller of two meshing members as a result of interference between the tip of the larger member and the root of the smaller member. If undercut were not produced, or the need for it were not reduced as mentioned above, then this interference would prevent rotation of the members.
I think the only reason for reducing undercut is to widen and strengthen the pinion tooth at its root, and this is an important reason.
I think shaper cutters are designed with modified involute shapes and tip protuberances, so the undercut produced probably depends somewhat on cutter design.
A hob cutter is a rack form with well defined design, so the undercut it produces results from the number of teeth in the workpiece, the amount of OD enlargement and the added distance the cutter is "held out" to produce the correct whole depth.
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