screw driving shaft, bearings, and the leadscrew can then
(4) Air operated carriage fronts and also collet chucks
be withdrawn as a unit, Figure 5. Shown on the end of
are centered with the die head's center of rotation as
the leadscrew shaft in Figure 5, the bearing thrust plate is
easily removed by removing four screws.
(5) The taper pins which join the leadscrew to its
coupling are removed. The leadscrew is turned end for
end and the new pin holes are drilled and reamed to join
the coupling with the end previously supported by the
outboard bearing. Drill and ream the leadscrew and its
coupling as a unit at the point 1800 from the existing
holes in the coupling. Also, have the pins enter the unit
from opposite sides to distribute the torque load evenly.
(6) A careful check for burrs should be made on the
lead-screw end removed from the coupling to assure that
it will operate freely upon insertion in the outboard
(7) When drilling the coupling and
new leadscrew end,
care should be taken that cuttings and other foreign
(1) Excessive horizontal and vertical clearance between
the carriage and bed ways may be corrected by removing
shims from the carriage gibs. A single gib #186, Figure
f. Leadscrew Nut Replacement
20, Page 20, is located on the left hand side of the
(1) After extensive usage, the leadscrew nut segments
carriage to remove horizontal clearance. Two gibs #187,
described above will require replacement to maintain lead
Figure 20, Page 20, are located on the underside of the
carnage to eliminate vertical clearance.
(2) To replace the nut segments, it Is recommended that
(2) In the event that reshimming does not correct
the carriage be removed from the machine. This can be
excessive clearance, rescrape the mating surfaces of the
accomplished by removing the outboard leadscrew
carriage gibs and, reshim the assembly accordingly.
bearing and moving the carriage rearward until it is
disengaged from the bed ways. On 12C, 16C and 20C
a. Carriage Fronts
machines, it is recommended that the carriage front or
(1) To produce concentric threads, the carriage fronts or
vises be removed before attempting to lift the carriage.
vises, #168, Figure 13, Page 15, must be centered with
To do this simply loosen two clamping bolts A , Figure 6.
the die head's center of rotation. The carriage fronts are
properly centered prior to shipment, however, they may
need to be recentered due to heavy usage, when grips
are replaced, turned, sharpened, or when the carriage is
reshimmed as described in the foregoing section.
(2) To determine off-centerness, place a piece of ground
cylindrical stock in the grips. Attach a dial indicator to the
die head by removing the chaser clamp screw nearest
the bore of the head and insert the dial indicator as
shown in Figure 6. Rotate the die head with the indicator
in contact with the stock. This will show the off center
relationship of the carriage front to the die head Total
allowable off center tolerance is 001".
(3) To recenter the carriage front, loosen the two
clamping bolts A, Figure 6, which secure the fronts to the
carriage. Rotate the four adjusting screws B, until the
fronts are centered. Adjustments for both right and left
hand carnage fronts on a double spindle machine are
made In the same manner.