Jim Wilkins wrote:

Do you feel that there is an incremental benefit in this method
rather than just making 8 passes of 0.075" from the initial hole
increasing the depth by
0.050" each time?
-

Both work, to me the quill feed with clip-on depth stop is faster and
easier than cranking the table, and only the end dulls so I can
resharpen the endmill without reducing its diameter. I usually advance
0.1" per plunge for a 1/4" endmill and 0.2" for 1/2", or less if the
end mill deflects too much. Generally the slot cleans up with one
final full-depth pass, unless it's a bearing surface like a dovetail,
then I experiment to find a feed rate and cut depth that give a good
finish before cutting to the final size.

That's 0.1" not 0.01" like Roger suggested? 'Cos my slots are only 0.075" at
the most.

Just so I understand your method:
1) Drill undersize
2) Plunge full size full thickness.
3) Move (in my case) 0.075" + plunge again.
4) Run the mill back to the original position to clean up the "tits".
5) Presumably run the mill back again over the same path to allow for the
differences in the type of milling on either side of the slot.

That has a nice ring of simplicity to it suited to my caveman style even
though Roger mentioned a possible issue with 4) and 5) making the slot too
wide.

For reference, last week I milled DB9 connector slots in thin plastic
boxes with a 1/4" carbide end mill on a Bridgeport and saw sideways
deflection on the first pass.

You mean the mill deflected or the boxes?

--
Michael Koblic
Campbell River, BC