Just throwing a little fuel on the fire... I have a very old traversing
head shaper where the head mechanism slides via the sliding key in the
shaft method. It's worked for over 100 years with some fairly high
pressures on a 1" shaft and 1/4" gib key. Yes, there is a bit of slop due
to the sliding fit of the key but neither the key nor the shaft keyway
have any specific bend or mushrooming or shearing from the thrust. It
works, although not if you want high precision.

Koz

As good precision as you get on a chain drive, it stretches anyway. I'll
bet all those shaper parts are hard, aren't they?