29
PM-236 v4 -207.indd
Method 2
(continued)
Install the drill rod in a collet or independent 4-jaw chuck with about 5 inches protrud-
ing. Center drilling is not needed.
Adjust the chuck for minimum runout at position ().
Check the runout at (2). Pointer movement when traversing is not a concern at
this stage.
If the drill rod is perfectly aligned with the spindle axis, there should be no differ-
ence in TIR at () and (2).
If there is a significant difference in TIR* from () to (2), try to correct this by loos-
ening, then re-tightening the chuck/collet, while levering the outer end of the rod
(gentle tapping with a non-marring hammer can also be helpful). When the runout
at (2) has been minimized, re-check at (), then repeat at (2), etc.
When (and only when) the TIR at both locations is the same, or very close, can it
be said that the rod is concentric with the spindle.
Compare dial indications when traversing from () to (2). Ideally, there will no
change, Figure E.
*
Factors that may affect runout:
Straightness and roundness of the drill rod;
Chuck installation (check for cleanliness and tightness); "Pointing accuracy" of the
chuck (the gripping surfaces of chuck jaws may not be parallel with the axis of the
chuck and spindle — especially likely if the chuck is worn).
Method 3 - Morse Taper Test Bar
This is a catalog-only item available from many suppliers (depending on the source
it may be named differently). The test bar in Figure F has a tapered shank to fit the
spindle, and a parallel portion several inches long. The diameter of the parallel por-
tion is unimportant. What matters more is its finish and lack of taper— check before
installing. Whatever taper there may be can be allowed for in the alignment test, as
Figure E. Runout should be less than 0.005" TIR.
.
2.
3.
4.
5.
6.
Figure E
Perfect alignment:
zero indicator change be-
tween locations 1and 2
Figure F
Morse taper test bar
