PRECISION MEASURING AND GAGING - OD1642 - LESSON 1/TASK 2
Material
Millionths of an inch
Steel
5.5 to 7.2 per degree F
Iron
5.5 to 6.7
Phosphor bronze
9.3
Aluminum
12.8
Copper
9.4
Gage blocks
6.36 to 7.0
(e) 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 only.
NOTE
Avoid conducting body heat into the block by careless
handling. Body heat may raise the temperature of the
block, causing serious error in a measurement,
particularly if a long stack of blocks is being
handled.
(f) When using gage blocks, consider the source of error resulting
from the 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 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.
(g) The temperature of the work may be either lower or higher than
the room temperature as a result of a machining operation. This difference
may be sufficient to cause a sizable error.
(h) 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 pounds.
(i) Gage blocks are used in the layout and checking of tools,
dies, and fixtures. They are also used in machine setups, in checking parts
in the process of being manufactured, and finished parts.
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