On 9/4/2010 11:01 AM, Morgans wrote:
"J. wrote

This particular bit is clearly marked "Max 870 RPM".

If you know of such a chart online I'd like to see it. All the generics I
find say 500 RPM for hardwood.

I still think that the bit has lost temper, if it was getting as hot as
straw temperature, as you were saying. Straw temp is for making steel soft.

I'd be inclined to agree with you if it wasn't yellow all the way up the
shank. I'd expect some blue somewhere around the edge if it got hot
enough to go yellow all the way up, but there's no blue on it.

Bad for bits. You now must get the bit up a bit hotter than straw and oil
quench it to get hardness back.

Assuming it's an oil-hardening steel.

Another question, about how you sharpened it. I hope this is not insulting,
but I have seen bits sharpened very wrong, before.

The leading edge angle of the cutting edge is critical. If you sharpen the
leading edge, it must be sharpened all of the way up the face, to maintain
the angle of the leading edge of the cutting surface.

Yep. Diamond file places in contact with full face and full face
sharpened. Sharpening Forstners is easy. And it cuts fine in
everything but ash.

The angle of the bit
behind the cutting edge is critical, too. If it does not go upwards rapidly
enough, the bit will not be allowed to cut as thick of a chip as necessary
to cut without burning. The chips coming out of the cut should be thick,
and long, not too unlike a sharp bit cutting steel. It will not be a
curly-cue as steel would be, of course, but the chips should be much thicker
than dust from a circular saw. Even if it is not sharpened correctly, it
will still cut fairly well in softer woods.

What comes out of it is the same quality of chip that I get from a block
plane.