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Milling machine spindle runout

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  • #16
    Wells index, as of last spring, wanted $295 for a touch up grind. They will inspect, clean and repack the bearings for $100. If new bearings are required it is $500+ for the bearings. I paid C&M $1k for bearings and a regrind in the quill for my BP CNC series II. I forget the exact runout, but it was over .001". The difference in smoothness was night and day when I got it back. Runout will kill small endmills fast.


    • #17
      OK, as JT said poor quality bearings might well have a non-concentric inner race

      But let's assume that you have reasonably good bearings with a concentric inner race. One indicator that this is in fact the case would be to check for runout on an external nose feature of your spindle. And while you're at it reef on the spindle with the help of something longer you can get a good grip on and check for play.

      If you get runout perhaps check that the nose is actually round by mic'ing the nose across 6 or 8 diameter angles. Perhaps a past crash of some sort bent the spindle or pushed out a portion of the metal at the nose. This could well show up by the spindle nose being slightly egg shaped when mic'ed across a few different angles of diameters.

      If the nose checks out then get a dial or test indicator tip up into the ID at the mouth of the taper.

      If you had some runout on the OD and the mic showed that it is truly round to within a very small degree then mark the high and low points of the runout on the OD. Now check the ID and see if the high and low points of the runout of the ID match the same for the OD. That might tell you more about this as well.

      None of this will true up the bore but hey, it's a start on at least understanding what the condition is of the spindle.
      Chilliwack BC, Canada


      • #18
        Click image for larger version  Name:	_IGP2435.jpg Views:	0 Size:	411.9 KB ID:	2003058 Click image for larger version  Name:	_IGP2434.jpg Views:	0 Size:	426.7 KB ID:	2003059 I bought a new R8 spindle intended for one of the Chinese small mills for about £36, and joined it by threading the parts to the splined top half of the Tom Senior light vertical mill. This was to convert from MT2 to R8. Even with the join, and the bearings being on opposite halves, I managed to get excellent runout. The concentricity between the R8 taper and the bearing seating was effectivly zero, and the mill is better than 0.0002" tir in working condition. If the op's mill is one of the Chinese ones, it might me very worth while getting a complete new spindle and a pair of good quality taper roller bearings, Timken or SKF.
        Last edited by old mart; 06-03-2022, 02:59 PM.