I know that there are a bunch of factors, but given average speeds, what seems reasonable for a 1/8 end mill (high speed steel). It looks completely scorched after being used for about 20 hours, mostly in mdf. Maybe how it looks isn’t important since it seems to cut fine still. My last use of it had some flaws but they don’t seem related to the bit. I didn’t expect it to be great or anything, it was cheap, I just don’t know how to determine if it’s worn out.
Heh, that should be Expectancy.
That usually means you are cutting with too high of RPM of too low a feedrate. I am not actually sure how long they last. I usually end up hitting a screw or some other dumb thing before they go bad.
When it is worn out/dull the edges of your cut will start to be worse, and I usually notice it in the top surface first.
Yeah, I started with some really slow cutting on the first few uses but didn’t actually see any scorching until the last few and those were usually when making small details like drilling a hole or making a pocket not much bigger than the bit.
I was up to cutting at 1500 mm/min on the last use, but maybe that’s too slow for MDF which seems very easily milled.
It seems every answer leads to another question. 
I think I’ll follow some advice I read in here somewhere to search for default feeds and speeds by material type and see where that gets me.
Also, a box of ball nose bits showed up in the mail so I have more than just the 1 bit as of today.
Try not to drill holes with ball ends, they don’t like it very much. All my end mills are carbide, so they usually break before getting really dull.