Milling: creating a smooth end finish in a slot

[Rob Meades]

The machine purchased was specifically stiffened for cutting brass; at least, that's what they told me, there was an extra stiffening bar, out of sight up-top in the picture of the machine above, for this purpose. I have a feeling that the mess you see on that last picture is because the tool had degraded by that point and hence was rubbing. If the machine were too sloppy, I'd have thought the same mess would appear early on as late on (see right-hand side of middle picture versus left-hand side)? Maybe a better question would be: could lack of machine rigidity somehow cause damage to the cutting edges of the bit?

It is worth noting that I'm cutting a very long continuous slot here as this is a maze that I'm cutting.

Plunge rate is 0.3 mm/sec. Not sure about spindle run-out: how would I go about checking it?