TM 9-4910-579-14&P
MICROMETER SPINDLE LOCK ADJUSTMENT
In setting the boring tool for size, the micrometer is automatically held against a stop in the boring head by spring
pressure on a ball which enters a groove in the micrometer spindle. The spring pressure on the ball is adjustable by
means of a setscrew in the side of the boring head. See Figure 9.
In setting the tool holder in the boring head, the spring pressure on the ball must overcome the spring pressure of
the plunger in the tool holder so as to hold the tool holder in the proper position while being locked in the boring
head. The spring pressure in the tool holder will vary according to the position of the plunger in the tool holder.
If the setscrew for adjusting the pressure on the ball is backed out too far, it is possible the end of the micrometer
spindle will not be held against the stop in the back of the head. This will cause the machine to bore oversize at
times and make it impossible to secure uniformity of bore sizes.
Whenever difficulty is encountered in sizes or uniformity of bore sizes, this adjustment should be checked. The
setscrew should be screwed in until it stops, and should then be backed out one-half turn. There should be a
distinct click when the ball enters the groove of the micrometer spindle and thrusts the end of the spindle against
the stop in the boring head.
This machine is equipped with a special adjustable micrometer stopscrew in the back of the boring head. See Page
-15 - Figure 9. This stopscrew should not be moved to correct micrometer setting and adjusting as moving it in any
way will require a readjustment of the micrometer as discussed in a preceding paragraph. Page - 16 - Under
Heading IMPORTANT .
The preceding paragraph explained the principle of the ball and spring pressure applied to the groove in the
micrometer stem. This special stopscrew is adjusted so the ball that applies pressure to the groove in the
micrometer stem just breaks over the edge of the groove and holds the micrometer tight against this stopscrew. If
at any time it is necessary to change micrometers or if the mike screw develops end play in the boring head, this
screw can be reset to position the ball properly at the edge of the groove on the stem so the micrometer will snap
into the boring head and be held firmly without end play. Whenever a readjustment of this screw is necessary, it is
extremely important that the bar be set up on a scrap block and the micrometer again be reset as explained in the
paragraph under the heading IMPORTANT Page - 16 -.
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