I ran these numbers through my G-Wizard feeds and speeds calculator and came up with the following:
For a 1/4" carbide 2 flute in aluminum, assuming a max spindle rpm of 4000 (not sure what it is on those siegs), a full width slot would be cut at 16 IPM. However, if you drop back to a light cut (probably better for a light mill anyway) and use High Speed Machining techniques (radial chip thinning is the buzzword), you can cut a 0.010" depth of cut at 80 IPM.
There are parts in between, of course, but anytime you cut less than 1/2 the diameter of the cutter, you can take advantage of chip thinning and just increase the feedrate. For example, a 40 thou depth of cut can run 40 IPM.
The trick is knowing how much. Those calculations are what G-Wizard does.
If you want to try it, go here:
http://www.cnccookbook.com/CCGWizard.html
Chip thinning is cool stuff. I was cutting some steel at 35 IPM
the other day and it was smooth as silk on my IH mill. Very quiet, nothing got too hot, and life was good. I would not have suspected I could go that fast as without the chip thinning calculation, the suggested speed would be single digit IPM.
Cheers,
BW