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The only parts of the cutter that really cut are: the top plate edge, the corner (or 'point'), and the upper part of the side plate edge.
The gullet does not cut, but helps to carry away the chips.
Sometimes, sharpening guides only position the file to hit those important areas, and the gullets get neglected. This can result in a negative slope to the cutter, instead of the familiar 'C' profile, and the tooth will not cut well, even with sharp edges. Below, is a an extreme example:
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Periodically cleaning out the gullet, to restore the original profile will improve performance. I do this with a file (any diameter) after sharpening the edges, or with the grinder wheel, again, after grinding the edges.
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'Buckin' Billy Ray' has really emphasizes '
get the gullet!" in some of his YouTube videos. If you keep up with them as you sharpen, just like keeping up with the depth gauges, it's not a big deal.