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.

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

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.

With cut chips present in the cutting area, the endmill is frequently
jamming as it's rotating, causing the endmill to try to cut fresh material,
plus the thickness of the chip(s) passing by the flute on the opposite side
of the endmill.
Chip interference can be heard as clicking or crunching sounds as the
endmill is cutting.
Some erratic table movement can probably be detected by placing a finger at
the point where the table dovetails meet.

The two conditions will lead to a wandering cutting path. The limited
rigidity of the minimill may also be a contributing factor.

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.

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.

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.

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.

The type of dispenser bottle I prefer for cutting lube is the wash bottle
with 90 degree spout shown near the bottom of this page (but in a 6oz
version)

http://www.zeph.com/dispensing-bottl...-dispenser.htm

or

http://www.2spi.com/catalog/plasticware/plast4.shtml

These types of squeeze bottles doesn't need to be inverted, and the tip
allows very good visibility of the work area.

--
WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html


"Michael Koblic" wrote in message
...
I need a small slot in my sundial bases. Usually I pre-drill the hole
(either 3/16" or 1/4") and then extend by 0.075" (1/4" hole) or 0.50"
(3/16" hole) the material is 3/8" key stock, galvanized, made in USA. The
mill is a generic X2, the mill bits are Chinese box set.

I have been using the side of the mill doing the full thickness all at
once. The slots have been coming out skewed which was visually obvious
even at these short distances. The wise was checked and is fine (0.001"
over 4" parallel).

Today I decided to experiment. First I did this:

http://www.flickr.com/photos/2768312...n/photostream/

then I progressed to this:

http://www.flickr.com/photos/2768312...n/photostream/

and this:

http://www.flickr.com/photos/2768312...n/photostream/

with the final event documented he

http://www.flickr.com/photos/2768312...n/photostream/


I interpret this that doing the full thickness slot is a bad thing,
presumably the mill is conventionally milling one side of the slot and
climb milling the other with resulting sideways movement. I have not seen
this documented elsewhere so my question is: Do those with the Big Beasts
see the same thing? Is this a reflection on poor rigidity of my mini or is
this a universally bad procedure to do the full thickness at once?

The other question is the mill bit: I think I milled less than 10 slots
with this particular one. Am I unreasonable expecting it to last longer?
Was it my technique or the provenance of the bit? Are there manufacturers
I should look to preferentially for replacement?

Thanks,

--
Michael Koblic
Campbell River, BC