Excessive spindle run-out

[summat]

I've recently bought a rather modified StarMill, originally with ATC but this was removed prior to me, and converted to Mach3. As part of the modification the previous owner rebuilt the bearings.

I've measured the run-out at the tool-tip and I'm getting 0.2mm( ), and even at the spindle holder I'm getting 0.05mm. (piccy attached, I hope).


Here's the thing, though - the spindle is quite rigid in the bearings - if I apply force in any axis there's no real play. As I revolve the spindle by hand, the "high" point on the DTI is coincident with the rotational angle of the spindle, and this translates to the offset at the tool-tip.

[Edit]... and for completeness, dialing the spindle above the bearing, the high point is 180 degrees opposed, so it is rotating around the bearing mount. [/Edit]

Now, my brain isn't geared for analysing three dimensions, but it would appear to me that rather than being necessarily a bearing issue, this is more likely an issue with how the spindle is sitting in the bearings (e.g. conceptually - a bit of swarf between two machined surfaces). Is this likely?, or am I relieving myself into the wind? ( ).

Any suggestions of where to start? (I'm minded to remove the lock-nut on top of the spindle pulley and see where that takes me - is that a silly idea?)

Any advice gratefully received.

Mike

[Martin]

Just tighten the tab nut a couple of tabs

[summat]

@Martin, cheers for replying - I've ordered a 58mm C-Spanner to give this a try. Any clue as to how tight this nut should be? 4 white-knuckles?

[TDIPower]

I think you will find 3 white knuckles and a grunt but you could push it to 4.

Pete