Civil Engineering Reference
In-Depth Information
Fig. 5.1. Some sort of digital readout is essential to accurate working on the milling
machine.
DIAL TEST INDICATORS
Another indispensable piece of equipment is a dial test indicator. This is used
for testing that various milling machine accessories are set up square and
parallel to the machine's table, as well as setting up and checking the actual
workpieces.
There are two main types of dial test indicator: the lever type and the plun-
ger type dial test indicator, which is sometimes known as an elephant's foot
indicator as the working end reminds you of an elephant's foot.
The lever dial indicator usually works both ways; it will indicate a forwards
or backwards movement. Some lever dial indicators indicate movement both
ways while some require you to flick a little lever to change the direction of in-
dication. This type of indicator has a relatively small movement, often a max-
imum of 15 thousandth of an inch (0.4mm) either way. This is not a problem
as you can normally move the stylus to where it needs to be, either by off-
setting the dial test indicator in relation to the zero position or by moving the
stylus, which is usually held in place by friction.
The plunger dial test indicator has a plunger that slides in and out and is
geared internally to a needle that rotates within a dial. The movement of a
plunger dial test indicator is usually about
1
⁄
2
in (12mm) but it can vary right up
to 2in (50mm).
