Reply by paratrooper34

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Posted on Forstner bits

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915 posts in 2973 days

#1 posted 02-22-2013 04:45 PM

Monte, I agree with Kazooman, the second video shows how NOT to sharpen a forstner bit. When you sharpen these types of bits (including the self-feed types), you only sharpen the flats on the angled part of the bit, just as seen in the first video. When you sharpen the flats on the bottom, you risk changing the geometry of the bit. As you see in the second video, he sharpens the area on the inside perimeter of the bit, but the rotary tool does not sharpen all the way to the edge. This leaves a small portion of that area slightly longer. When you move to sharpen the flats on the bottom, you effectively change the depth of that area in relation to the small unsharpened portions on the perimeter. That will then leave you with a bit that will not cut because the small portions that are deeper on the perimeter will not allow the cutting surface on the flats to actually reach the wood. If you only (correctly) sharpen the angled area, you will not change the depth of the bit.

Hope that made sense. Good Luck!

-- Mike

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