LATHE OPERATIONS - OD1645 - LESSON 1/TASK 3
The procedure used in checking the accuracy of the thread is to first select
the proper micrometer, then calculate or select from a table of threads, the
correct pitch diameter of the screw.
Lastly, fit the thread into the
micrometer and take the reading.
(3) The ring gage (female)(figure 48 on the following page) is screwed
onto the thread after it is cut. It checks the completed thread against a
standard mating part. By means of a ring gage, the oversize and undersize
sections of a thread can be found.
Ring gages are made in a variety of
sizes and fits. The gage must be carefully chosen to control the desired
limits for each thread as determined by the design engineer. Overly close
limits mean high manufacturing costs, while overly wide limits cause
assembly failures. Gages should be selected in accord with the class of fit
for which they are used. For example: if a blueprint calls for 9/16-12UNC-2
thread, it means that the ring gage needed will have a major diameter of
9/16 inch, with 12 threads per inch of the Unified National coarse type, and
it should have a class 2 fit.