Need Help!- Burning my brass?!?

[Micro Milling]

I"m not sure whats going on, or if the bit is getting worn. But I noticed that my bit gets very hot. It got so hot it left burnt marks around my brass I was milling, and the brass is maybe max 1/8 inch thick.

What is wierd is that if I mill higher up on the end mill, it seems to cut much easier.

I have a couple of questions I was hoping someone could answer.

When an end-mill starts to wear, does it cause much more heat and cause this blank buring of the brass? I'm milling small peices of brass maybe 1 inch cuts max on a maybe 1/4" end mill.

How long do end-mills last, do they need to be replaced often if your cutting mostly brass?

Since the brass turned a bit black around a couple of cuts, is there a way to remove this black burnt brass? Will polishing get it out, or is it burnt black to the middle?

[packrat]

quote Micro Milling "What is weird is that if I mill higher up on the end mill, it seems to cut much easier." > Thats because your using a sharper area of the cutter<

quote MM "When an end-mill starts to wear, does it cause much more heat and cause this blank buring of the brass?" > Yes. Dull cutter rubs not cut, causing heat in both cutter and part. ? Does that make it a "rubber"?<

quote MM "How long do end-mills last, do they need to be replaced often if your cutting mostly brass? > Depends! On spindle RPM, feed, type of brass. I'm new to the group, but 45 years as tool and die maker, from what I've read here most people use too much spindle speed.<

quote MM "Since the brass turned a bit black around a couple of cuts, is there a way to remove this black burnt brass? Will polishing get it out, or is it burnt black to the middle?"
>It's just oxidation, it will polish off.<

[Mcgyver]

Originally Posted by Micro Milling What is wierd is that if I mill higher up on the end mill, it seems to cut much easier.

you'd expect the bottom to be more worn right? typically it would see more action so what you've observed is to be expected

When an end-mill starts to wear, does it cause much more heat

Yes.

you left out the most important info - cutter dia and speed. Listen to what packrat said - the theoretical speed (which you calculated, right?) is just that; the speed just before the line on the cutter wear chart changes slope. Your cutters will remove more cubic material if run below this and with a decent depth of cut and feed. Leave theoretical speeds to production where tool costs get balance against overhead....different economics apply to the home shop

Also, ideally use a new cutter for brass and keep it for brass. Cutting tools, from endmills to files, don't work as well on brass if they've been used on say steel