Posted by Bill S on April 01, 2001 at 21:35:06:
In Reply to: 615a Fellows Gear Shaper Adjustment posted by Josh Ward on March 31, 2001 at 15:26:14:
How much variation in tooth-to-tooth (TT) spacing are you seeing? If the gear tooth number is an exact multiple of the cutter teeth (or vice versa) then you might suspect cutter tooth-to-tooth spacing variation. Cutter variation might be due to improper cutter sharpening, a few dull teeth, or cutter manufacture. If there is a multiple relationship between cutter and gear, try a different number of cutter teeth.
Usually there are two rotations to a cutting cycle, roughing and finishing. The finishing cut transfers the cutter's profile variations to the gear. A dull edge on one tooth, because of tool rake angle and excessive back force, can affect tooth profile.
Thus a shaper-cut gear can be no better quality than the cutter that makes it, with the following exception:
Using two (or more) rotations after the finishing cut usually averages out cutter variations. This basically defeats the shaper's productive edge over a hob, however.
Another consideration with shapers has to do with overlap at cycle end. A shaper's finish cutting cycle typically removes a slight amount of material from the last (overlapped) teeth, and produces a thinner tooth or two, esp. with harder materials. Try letting the machine cycle several times on a single workpiece before removing it to see if tooth thinning and variation is reduced.
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