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PM 728V-T v2 2020-10
Copyright © 2020 Quality Machine Tools, LLC
VISE KEYS
Most precision vises come with key slots on the underside ma-
chined exactly parallel to the fixed jaw. Key slots, Figure 3-21,
can be a great time saver. Properly installed they allow the
vise to be removed and replaced routinely, accurately enough
for general machining
without the need for indicating every
time.
Most 4” vises have either 14 mm or 16 mm slots, calling for
shop-made T-shape adapter keys as Figure 3-22. It is well
worth the effort to make these precisely. Aim for a snug fit in
both vise and table, but not so tight that it takes more than a
small amount of effort to lift the vise clear. Case hardening is
recommended, with final fitting using a fine stone or diamond
stone.
INSTALLING & INDICATING A VISE
For routine milling operations the workpiece is held in a preci-
sion vise. For the PM-728V-T a 4” vise is most suitable.
“Indicating” means checking the alignment of the fixed (back)
vise jaw relative to the axis of table motion.
Install the T-bolts and align the vise by eye. With one of the
clamp nuts snug, but not tight, tighten the other one just short
of fully-tight (but tight enough so the vise won’t budge without
a definite tap from a dead-blow mallet).
A typical setup for indicating is shown in Figure 3-20. There is
no spindle lock, but you need to
make sure that the spindle
does not rotate
throughout the procedure — it helps if the low
spindle speed is selected.
Set the indicator tip against the upper edge of a precision ref-
erence bar or, if not available, use the front face of the fixed
jaw of the vise instead (check for dings, hone if necessary).
Adjust the Y-axis to pre-load the indicator to mid range at the
tightly-clamped side of the vise, then lock the Y-axis.
Note the indicator reading, then watch the indicator as you
traverse the table slowly toward the loosely clamped side —
watch for any sign of spindle rotation
. Ideally, there should
be no discrepancy between the indicator readings at the two
ends — unlikely at the first attempt. Return the table to the
starting point, then repeat the process, tapping the vise in as
you go. Repeat the process as often as necessary for the de-
sired accuracy, progressively tightening the “looser” nut. Now
fully tighten both nuts, and re-check again (tightening a nut
can itself introduce significant error). An established routine
like this – tight to loose – can save a lot of time.
Most users aim for an end-to-end difference of not more than
± 0.001” over the width of the vise jaw.
Figure 3-22
Shop-made vise key
Dimensions in millimeters
Figure 3-21
Vise keys installed on X-axis
On most vises the keys can also be installed on the long axis.
Figure 3-20
Indicating the vise
The tip of a standard dial indicator, arrowed, rides along the side face
of a ground reference bar (or the front face of the back jaw).
