Wild_Bill wrote:
It would seem to me that if the cutting path errors aren't caused by
unintended table movement, then the wandering path is likely to be
caused by flexing of the endmill.

If I had to place my money it would be the column, given the spring-back
phenomenon I described elsewhere.

It's not easy to see the length of the endmill, or just the cutting
section of it, from the photo.

5/8"

Another significant problem that happens when a small endmill is used
to cut the full width of a slot, is chip evacuation, or lack of it.

I woudld have thought the contribution of this would be small over a 0.075"
but perhaps not altogether negligible.

snip


Using a cutting tool lubricant in a squirt bottle, to constantly
flush the chips out of the cut should improve the results, but the
sides of the slot probably still won't be perfectly straight.
The spiral of the flutes will help carry chips away, but only to a
limited degree (less at lower RPMs). Using a medium viscosity cutting
lubricant will help the chips flow outward from the cut.

I tried both RapidTap and squirting a water /oil mixture. I did not see much
difference except for the mess with the squirting.

The other recommendation of drilling the ends of the slot location
with a rigid drill, followed by material removal with a smaller
diameter endmill would likely be the best procedure, especially with
a light duty machine.

Drilling 1/4" holes 0.075" apart is well beyond my skill level.

Flooding a cutting tool lubricant to flush chips away can obviously be
fairly messy, so coming up with a method to recover and contain the
lube might be worthwhile.
A small endmill isn't going to be slinging much lube, but the flooding
action should be constrained to the table area.

The squirt bottle does enough slinging...

It might be possible to retrofit a gutter system around the edge of
the table, or the workpiece clamping methods might need to be
reconsidered, to allow the small parts to be cut with them sitting in
a shallow pan on the table.

Or I could just cut the slot in small passes as it seems to work :-)


--
Michael Koblic
Campbell River, BC