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Copyright © October 2017 Quality Machine Tools, LLC
PM-1440E-LB 11-13-17 V1
CROSS-SLIDE & COMPOUND BACKLASH
When alternating between clockwise and counter clockwise
rotation, the cross-slide handwheel may move freely a few de-
grees but the cross-slide table stays put. There may also be
similar lost motion in the compound. The acceptable amount
depends on the user, but 0.005” is generally a good compro-
mise. Smaller numbers are possible, but overdoing it can lead
to premature wear of leadscrew and nut.
Lost motion is due to two factors: 1. End-float (in/out move
-
ment of the handwheel) caused by insufficiently tight coupling
of the leadscrew and thrust bearings. 2. Wear in the leadscrew
nut.
Factor #1 is correctable in both the cross-slide and compound.
Leadscrew handwheels on the PM-1440E-LB — cross-slide,
compound and tailstock — are attached in a similar way, Fig-
ure 4-13. The handwheel is locked to the leadscrew shaft by
a key (not shown). It is held in place by a flange screw in a
threaded well at the outer end of the leadscrew shaft. An in-
ternal locking set screw, bottomed in the well, prevents loos-
ening of the flange screw. To correct backlash due to loose
coupling between leadscrew and thrust bearings, back out the
set screw a turn or two, then tighten the flange screw using
a pin vise or needle-nose pliers. Do not tighten to the point
where the thrust bearings are over-compressed, resulting in
uneven motion. Back off for smooth rotation, with no appre
-
ciable end-float. Re-tighten the set screw. This tends to back
out the handwheel a small amount, so check end-float again.
Factor #2 is correctable in the cross-slide by compressing
the leadscrew nut, Figure 4-14. Remove the compound from
the cross-slide, then remove the socket head screw secur-
ing the cross-slide to the leadscrew nut. Turn the cross-slide
handwheel clockwise to drive the nut backward until it can be
worked on at the back. Ii not already installed, insert an M6 x
1 socket head screw, approximately 15 mm long, then tighten
the screw as necessary. Don't overdo this — a 45 degree turn
of the screw represents a backlash take-up of about 0.005".
The compound leadscrew nut is not adjustable.
Figure 4-13A
Handwheel attachment schematic
Figure 4-14
Cross-slide leadscrew nut
(representative)
Figure 4-13B
Handwheel attachment
