Posted by Bill Simpson on December 03, 1999 at 12:40:45:
In Reply to: PROPER HOBB SHIFTING PROCEDURE posted by JASON on November 28, 1999 at 23:17:58:
Hob shifting on some hobs is optionally automatic. Most, perhaps, must be manually shifted.
Hob shifting means to change the axial position of the hob cutter with respect to the workpiece. Usually you start a fresh cutter so that the end of the hob is near or just past the centerline of the workpiece. When the hob shows the slightest wear (light reflects off of the tip of the cutting edge), the hob is shifted to position a new tooth on center with the workpiece.
Barber Coleman makes hob sharpening machines which control angles and amount to remove. I certainly wouldn't try grinding acutter by hand.
If you are patient and careful, you could make an arbor fixture for a table grinder, and use a stop blade to position the gash. But it is so easy to ruin an expensive hob if you don't use a hob sharpener. In any event, take light grinding passes to avoid burning and softening the material.
Normally, you want to take the cutter out of service when light reflects off the top (gear root) cutting edges. This requires the least removal of material, which increases hob life.
Never run the hob until it shows wear along the top relieved surface behind the cutting edge. By that time the hob needs too much material removed, and the gears that were made near the end probably have excessive profile errors.
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