[raytor]

Can someone explain to me the feed rate concept for mini mills like the Sherline?
For example, 6061 alu has SFM of 280 - how would this relate for the rpm of the lead screw? Say I was turning it by hand, how fast would I need to turn the feed for a given sized end mill?

[cncwhiz]

Milling cutters need to run at a required "chip load". I run at "IPM", if your tool is a two flute end mill I would run it a .004 to .006 chip load depending on rigidity of the setup. Say your end mill is 1/2 calculated it would run at 2139 rpm at 17 to 25.5 ipm. The formulas for doing this are in the machinists hand book.

[DAB_Design]

Here's some helpful formulas from a quick google search. http://www.manchestertools.com/tech/1_10.asp

You would want the second one down, in the left column.

[Swami]

I have been using a Sherline 5410 for about 6 months.
I always run it at max RPM (2500), and then I also run it at maximum feed for my setup, which is about 330mm/minute. Then I adjust depth of cut until it sounds good.

For T6, that means I normally take between .8-1.1mm cuts for a 3/8" endmill going at 330mm/min and 2500rpm.

I hope that helps,
Swami

[Torsten]

The Surface Speed and Chip loads found in the Machinist Handbock are for
very large and rigit machinery on smaller machines you will have to derate
the values somewhat.
The important thing is the Chipload per tooth, each chip taken acts as a little
Heatsink removing the heat generated durring cutting.
It has to be of sufficient thickness to do this job a much tinner chip would
get much hotter and start melting wich causes it to stick to the cutting edge
and generate even more heat on consecutive cuts.
So when derating the values in the Handbock you want to reduce the chipload
to a value that will still provide a resonable thickness at a reduced feedrate the
Spindle Rpm can be calculated from there.

The most common mistake people make is to use the Surface speed found in
the handbock and simply feed at a much slower rate to suit the ridgidity of
there machine. This results in a very thin chip that will melt and stick.

Reducing your Spindle speed to match your chipload is much better.
Good Luck