I don't use a router often but recently I dusted both of mine off and
got a surprise. I was using a 1-1/4-inch x 1/4-inch shank flush trim
bit and I thought my router was broken.


But after some routing and closer inspection I found that the bit just
isn't stiff enough at top speed to remain straight. It is easy to see
it and when I tried to use it it was easy to feel it and hear it. It
caused the whole router to vibrate and caused a lot of chatter. I tried
in the other router and the same thing but to a lesser amount. I've got
a bit that has a 1/2-inch shank and finished what I needed.

Two things occurred to me.

1 the bit has two bearings and they both need to rest on the material
i wasn't doing that because the bit's longer than the material's
thick But even so a router bit needs to remain straight and stiff
and this doesn't at ~23,000/rpm

2 1/4-inch shank is not the way to go for a flush trim bit, needs
to be a 1/2-inch shank to maintain proper stiffness and avoid
the horrible deflection.


maybe it'd be ok at lower rpm but both routers are full on or
off