Thread milling cutterdia / hole ratio
Hi Guys,
I've been considering the purchase of some thread mills, but find myself wondering whether the milled thread geometry is correct, when the cutter has a diameter, for example, of 1/2" and the hole to be threaded is maybe 11/16 (for 3/4" NF). When the cutter diameter is an appreciable fraction of the hole size, there would be quite a bit of cutter sweep across the thread helix, which would tend to change (increase) the included angle of the internal threads somewhat.
This effect is plainly seen when milling helical gear teeth, wherein the gear cutter cuts a groove wider than the cutter on account of the entry/exit ramp of the cutter tooth. For this reason, a machinist actually uses a lower numbered cutter for milling helical gear teeth, than would normally be used for an equivalent spur gear.
Is this ever taken into account for thread mills, do you know?
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