Precision matthews PM-1440GS, Руководство пользователя

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Copyright © 2020 Quality Machine Tools, LLC PM-1440GS v3 2020-10
saddle by hand, then re-engaging, usually by reference to the
threading dial, Figure 3-20.
If the TPI number is divisible by 2 re-engagement can be done
at any line on the threading dial.
For all other TPI numbers every engagement, including the
first , must at the point where a specific line on the thread-
ing dial comes into alignment with the datum mark. If not, the
second and subsequent passes will be out of sync. In some
cases, Figure 3-20, there is a choice of lines for re-engage-
ment, but in every case the process calls for careful timing.
[ NOTE: Disengagement and re-engagement of the split-nut is
not applicable to metric threads].
Typical depths of cut per pass vary from an initial 0.005” or so,
to as little as 0.001”, even less. A finishing pass or two with
increments of only 0.0005” (or none at all) to deal with the
spring-back effect can make all the difference between a too-
tight thread and one that runs perfectly.
Assuming that the compound is set over at between 29 and
Figure 3-20 Threading dial visualization for selected U.S. threads
Minimize wear by swinging the dial indicator assembly away from
the leadscrew when not in use
30 degrees, the total depth of cut is approximately 0.69 times
the thread pitch, P (this equates to a straight-in thread depth of
0.6 times P). There may be a need for a few thousandths more
in-feed than 0.69P, almost certainly not less.
USING THE THREADING DIAL
Referring to Figure 3-20, the general rules are:
1. Divide the TPI value by 2: If this gives a whole number ,
example 10/2 = 5, re-engage at any line on the dial. Spe-
cial case: if the result of dividing by 2 is an even number,
example 12/2, you can re-engage midway between lines.
2. If the TPI value is a whole number not divisible by 2, ex-
ample 7, re-engage on the start line, or any line at right
angles to it. In the table this shows as 1-3-5-7 (but could
be 2-4-6-8, etc.).
3. If the TPI value is fractional, but becomes a whole number
when multiplied by 2, example 4-1/2, re-engage only on
the start line, or its diametrical opposite. In the table this
shows as 1-5-1 (but could be 2-6-2, etc.)
If in doubt, re-engage on the start line!