That makes no sense to me. If the motor was never loaded the bearings are
probably just fine. 30 minutes of cutting wood will generate a lot of
friction and friction generates heat and the heat will travel the path of
least resistance. That would be down the shaft and into the collet nut that
makes a good heatsink.

Did you grab the housing? Was it warmer near the top or was the collet nut
hotter than the motor housing? How hot was the bit?
Ed

The aluminium router base was warm to the touch, but aluminium is a
very good conductor and will draw heat from the collet anyway. The
bit was warm of course, but cooler than the collet nut. The nut
wasn't sizzling, but was too hot to hold onto. The bit was brand new,
and the pilot bearing on the bit has not siezed. From the very light
feed pressure required and the quality of the cut, I know the bit is
plenty sharp. I suspect the shaft bearing next to the collet is
failing, but I wanted to see if this kind of heat build up is normal
before I get too excited.

DonkeyHody
" We should be careful to get out of an experience only the wisdom
that is in it - and stop there; lest we be like the cat that sits down
on a hot stove-lid. She will never sit down on a hot stove-lid
again---and that is well; but also she will never sit down on a cold
one anymore." - Mark Twain