Flat Bottomed Hole

A special grind on a regular bit?

Done that. It worked fine in brass.

Pete Keillor

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| | A special grind on a regular bit?

In the aviation business we called them gunbarrels, but there are special drill bits whose purpose is to use the old hole as a guide to the new one, and there was little to no point on them. Sometimes we had to make our own gunbarrels, but it helped if they were done with bits that didn't have flute reliefs cut out, as they tended to cut into the metal you want to match drill.

Quick and dirty... (if it is a nice, standard size...)

Get a cheap end mill. Take a stone or small file and knock the edge of the sides of the flutes so it will only cut on the end...

Jerry

----------------- You can use an endmill. One of the few times an end mill will work in a Jacobs type chuck.

GmcD