Instruction Manual
Section Five
fixture lift Cam (No. 13) and reassemble the fixture Spindle Assembly
as described in l-F. This procedure will allow the fixture Draw Tube,
Collet, and Collet Adapter (all of the moving inner spindle parts) to
rotate freely together in a clockwise or counterclockwise manner. Lock
Screw (No. 25) should be tight so that the outer spindle (No. 18) does
not move. Loosen the thrust collar (No. 19) just enough so that the inner
spindle assembly is easily rotated.
3. Raise the Wheelhead so that the bottom of the wheel is just above one of
the tap gullets and centered over it in its mounted horizontal position
(e.g., see Photo 56). By moving the machine Crossfeed and rotating the
fixture movable spindle, place the wheel radius concentric with and tangent
to the gullet radius. Take care not to allow the tooth face to strike the
side of the straight wheel as this will destroy the radial rake on the face
of the tooth,
4. Since the toothrest position and its use in this set-up are similar to those
used in grinding a form relieved cutter, consult Chapter 9, Parts I and III
in this section for the general instructions relating to this sharpening pro
cess. Photo 56 shows the general position of the fixture and tap relative
to the wheel. The toothrest, placed on the table, indexes on the back
side of the tooth whose flute is being ground. If the tap is spiral, it is
mounted in the B942 fixture and the toothrest is fastened on the wheel-
head, as in Photo 39 of Chapter 9. Once the position of the tap gullet
relative to the wheel has been established, set the micrometer toothrest
to hold the flute against the stationary wheel. Do not move the Crossfeed
after this locating process has been completed as the proper rake angle
for the tap has now been set.
B. Grind the flutes in succession Grinding is accomplished by moving the fix
ture and tap relative to the wheel with the table traverse handwheel, while
at the same time holding the tap flute firmly against the toothrest blade
with the fixture handwheel.
1. After a trial light cut on the first flute, inspect the tap to see if the grind
is uniform along the length of the tap and to see that the original rake
is being maintained. Make necessary corrections, and then select a flute
gullet about 180 degrees opposite to the one just ground to see if the tap
is running true.
2. After the first light cut on all the flutes, move the tap away from the
wheel and rotate the tap in its cutting direction (AWAY FROM THE
TOOTHREST). Next, move the micrometer toothrest a slight amount in.
order to advance the flute face toward the wheel. Now move the tap
flute back against the toothrest blade. The index feed for the flutes per
pass should be no more than .001 inch on the toothrest micrometer. Heavy
cuts can set up a burr between the cutting teeth and reduce the strength
of the cutting edges.
C. Spiral Taps:
1. As stated previously, spiral tap faces must be ground with the use of a
B942 workhead or similar workhead with anti-friction bearings. Large
taps will require the use of a special long toothrest guide (SUCH AS THE
B670RB) as well as the use of the B647B Driver and a left side tailstock.
2. The grinding procedure is the same as described for hobs in Chapter 9
but modified by steps A and B above.
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