Problem- Arbor not running true

[CNC-Hammer]

Today at work I was presented with an odd problem. The arbor on an Adcock Shipley horizontal mill would run out of true when the nut was tightened ever so slightly. The operator with many years experience was baffled. Everything was clean, mating faces were skimmed where possible and anything clocked before and after tightening the nut but it still occured.

Has anyone experienced this before?

[HuFlungDung]

If all the spacers are clean and parallel, and no chips or galling inside the nut threads, then I would suspect the arbor is bent nearest to the drive taper end.
The arbor nut should only be tightened up with the arbor support bearing in its place near the nut, because it is possible to twist and bend the arbor with the offset torque applied to the nut.

You would have to analyse the bend, to discover where the maximum runout is, both with and without the arbor support. This should give you some idea of where to begin pressing it straight.

[CNC-Hammer]

Well the arbor runs quite well without the tightening. Even with the support on the run out is evident. I do think the problem is near the spindle end however.

[HuFlungDung]

Did you just install a new cutter on the arbor? Did you check the cutter for parallelism around the bore? Maybe it's a dud?

Other than that, there has got to be a bad spacer (out of parallel), perhaps one that got dented by the key. This is possible because Murphy is always watching to see if you checked the spacer rotations and lengths relative to the key length

[Geof]

A tedious approach, if you can take the key out, is mark the direction of runout, losen and rotate a spacer 180 degrees leaving all the others in the same place, retighten and check the runout. If it has shifted orientation the spacer that was rotated could be the cause. Test all spacers by rotating them back to where they were and rotate another.

[CNC-Hammer]

Originally Posted by HuFlungDung Did you just install a new cutter on the arbor? Did you check the cutter for parallelism around the bore? Maybe it's a dud? Other than that, there has got to be a bad spacer (out of parallel), perhaps one that got dented by the key. This is possible because Murphy is always watching to see if you checked the spacer rotations and lengths relative to the key length

The cutter is one that has been used previously and afaik is pretty good.

Spacer lengths and rotations?!?! Are you getting scientific now?