Maybe I can help. Tell me a few things:
1) machine type and spindle speeds possible?
2) stock material and size? Aluminum, stainless, cold roll steel, tool steel, ect.
3) size of finshed parts?
4) total depth of cuts?
5) is there coolant, air, or air mist available?
6) tell what type of cutter you plan on using if any? ie Carbide, HHS, number of flutes, coatings, LOC on the endmill?
I've cut most materials and with endmills from .006 diam. and up. 1/32 wide slots in p20 1/2 inch deep. You can cut almost any materials with the right cutters, machine, feeds and spindle speeds.
General rules are:
Ridgidly held stock.
Stiff machine (yes this is very important with small tools)
very good control of feeds and speeds
chip load and DOC... example .020 carbide talin coated 3 flt. 10% to 30% depth of cut, chip load about .0002 to .0003 per tooth in 303 ss or mild steel. Thats 5.6 in/min at 7500rpm and a depth of cut of around .006 to .007. Rate your cutter wear by the burr, if you can scrape it off with your finger nail it is still sharp. if not... it's about to break.
Robb Jack cutting tools had a good chart in their catalog, maybe you can find that info on the web.
I'll give some starting info...just answer my questions.