MAINTENANCE • MACHINE TOOL SPINDLES
After closure cap R is securely fastened to the housing, rear slinger D is placed in position against the inner-ring face of the ball bearing, and locknut S, having a left-hand thread, is screwed on the shaft with a spanner wrench handle with two sharp raps of a light hammer. The procedure is repeated from the opposite side by relocating the spanner wrench on the locknut 180 from the first position. The clearance between the closure cap R and the rear slinger D is checked with a feeler gage to make sure that no interference exists between the two parts.
Front locknut J is loosened counterclockwise about four turns and indicator readings taken at the wheel-end of the shaft, Figure 6,. If these readings correspond to the nose runout or eccentricity previously obtained when the shaft was inspected on parallel V-blocks before assembly, no inaccura- cies have been introduced through installation of the bearing. Following the check, the front locknut J is screwed on the shaft until the face of the front slinger C comes to bear on the inner ring face of the ball bearing. This locknut is set with a spanner wrench to tighten the bearing inner rings together and against the shaft shoulder, Figure 7. Tightening is done evenly and securely by striking the wrench handle with two sharp raps of a light hammer and repeating this operation on the other side of the locknut, 180 from the first position. Approximately the same force should be used in tightening the locknut every time it is tightened. This is important, especially during the trial and error scraping process.
Figure 6 – Checking Nose-End Runout
Once these bearings are locked by the locknut, they become a preloaded pair in a fixed position, and the spindle is checked for possible runout. Should runout now exist in the assembly, it can be attributed directly to the relation between the threads and the locking face of the locknut. If the shaft shows a runout of 0.0001 inch or more, it can be assumed that the trouble lies in the locknut contact with the outward face of the front slinger. If the locknut face is tightened against the bearing inner face without the locknut face being square with the threaded bore of the shaft, the shaft may be forced to bend. This shaft bending will cause a radial eccentricity (runout) as measured on the shaft. Scraping of the high points on the locknut face will eliminate this out-of-squareness condition and provide optimum running accuracy.
Figure 7 – Tightening with Spanner Wrench
Scraping Locknut to Eliminate Runout
To determine where to scrape, first check with an indicator over the front end of the shaft at point X, Figure 1, until the highest reading is noted. This shows that the tip of the indicator point is directly over the vertical diameter of the shaft. Stopping at the highest reading on the indicator, the shaft is slowly rotated from the opposite end of the spindle which, in this case, would be the drive or rear end. Stop at the lowest reading on the indicator dial and with a red pencil or metal-marking pencil scribe a line longitudinally along the shaft and on the outside diameter of the locknut J directly in line with the low reading.
MAINTENANCE MACHINE TOOL SPINDLES