Ignoramus17758 fired this volley in
:

In steel, however, this little 1/8" endmill works for a while, then
breaks after 1/2 hour.

Ig, you can probably hear what the problem is.

When the bit's tip starts to deflect and "orbit" about center, rather
than cutting true, you'll hear those little bits start to "sing" as they
make a cut. When you hear that "zzzziiiiiiinnnnnnnnnggg" sound, they're
chattering at enough amplitude to rapidly fatigue the metal.

I know you want to get familiar with small detail work... well... small
detail work involves hogging out all the excess stock you can with drills
and larger bits, then using lighter cuts for the finishing.

Tiny bits were never intended to remove large volumes of stock.

LLoyd