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Why doesn't my D bit cut?

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RotarySMP:
I got the half height nearly perfect. 10.98mm diameter cut and honed to 5.48mm There is 7° of clearance angle below the cutting edge, I was running in Backgear at around 250RPM but it didn't want to cut, just pushed away. The hardening must be okay, as the corner is still sharp.

Mark

DavidA:
Mark, that tool you circled in the picture looks as it it is for forming a flat bottom to a blind hole, or maybe for forming a flat 'ledge', maybe to clean up a counter bore for use with capscrews. Not for reaming. It doesn't appear to have any sloping 'lead' to shave the metal at the diameter.

Dave.

BaronJ:
Hello Mark,

From the info you have given you are trying to cut too much material away.  A "D" bit is more like a reamer and 0.6 mm is far too much. A tenth of a mm (4 thou ) would be more reasonable.  Particularly in a harder material like stainless.

SwarfnStuff:
Mark,
      I agree that you are possibly expecting a bit much of a "D" bit, however, here is one of the type I was thinking of doing much more.     
      It is being used to do the bore of a model canon 1/2" and 10" or so in depth. Took my friend ages at 2.5mm per peck, clean and go again - 2.5hr if I recall.
      He gave it a short starting hole of the correct diameter and the D bit did the rest. As you can see from the pic complete with chips it is much as I described with the off side keeping things from wandering. The barrel was brass, the bit of drill rod / silver steel and hardened after grinding and honing appropriate reliefs.
John B

RotarySMP:
I appreciate all your responses. Wasn't able to try fixing it yesterday, but should get back to it this weekend.
Mark

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