USING PRECISION GAGE BLOCKS - Continued
Shift the blocks. If the blocks are clean, they
will begin to take hold.
Slide the two blocks together, using a slight
pressure and a rotary motion.
Shift gage blocks so that their sides are in line.
Any combination of gage blocks may be stacked
together in this manner. The combination will
be as solid as a single block.
The adhesive force that binds two gage
blocks together is a combination of molecular
attraction and the suction cup action due to
the film of oil or moisture on the surfaces
wrung together. Separate gage blocks by
sliding them apart, using the same movement
as when wringing them together.
Do not leave blocks wrung together for long
periods of time since surfaces in contact will
tend to corrode.
FACTORS TO CONSIDER WHEN USING GAGE BLOCKS
Ordinary changes in temperature have a sizable effect
on measurements made with precision gage blocks.
The standard measuring temperature is 680F, which is
just a little lower than the average temperature in most
shops. Since the room temperature affects the work as
well as the block, the expansion in the work will be
matched in most cases by a similar expansion in the
block, The coefficient of linear expansion of several
metals and blocks is listed below:
Millionths of an inch
5.5 to 7.2 per degree F
5.5 to 6.7
6.36 to 7.0
Handle blocks only when they must be moved and hold
them between the tips of your fingers so that the area of
contact is small. Hold them for short periods of time
Avoid conducting body heat into the
block by careless handling. Body
heat may raise the temperature of the
block, causing a serious error in a
measurement, particularly if a long
stack of blocks is being handled.
When using gage blocks consider the source of error
resulting from temperature. Metals other than iron and
steel (such as aluminum) have a much different
coefficient of linear expansion which will result in a
difference between the room temperature measurement
and the standard measuring temperature measurement.
Careless handling of gage blocks may produce an error
of several millionths of an inch and this error increases
proportionally with the dimension of the block.
The temperature of the work may be either lower or
higher than the room temperature as a result of a
machining operation and this difference may be
sufficient to cause a sizable error.
Theoretically, the measuring pressure should increase
proportionally with the area of contact. For practical
purposes, it is better to use a standard measuring
pressure. The most commonly used pressure is 1/2 to 2
Gage blocks are used in the layout and in checking the
accuracy of tools, dies, and fixtures. They are also used
in machine setups and in checking parts in process of
manufacture and finished parts.
Gage blocks are commonly used in setting adjustable
inspection gages. Gage blocks are used to verify the
accuracy and wear of ring and snap gages and many
other special-purpose gages. The classification of
blocks depends largely on the accuracy required.
Typical classification is shown on the following page.