Galling is when small amounts of the material being tested weld
to the gage surface thus causing the gage to grow. There are some
materials, like stainless steel and aluminum, that are more prone
to galling gages. Small amounts of material can be transferred from:
Several conditions may increase abrasion.
Product thread manufactured too close to the maximum material
size. When this happens there is more gage to material contact as
the gage is applied. To avoid this try to keep the product size
near the mean.
No oil on the gage. Be sure that the gage is well lubricated.
By lubricated I mean oiled. I know that the part is covered in cutting
oil. While cutting oil is a cutting lubricant, it is not a gage
lubricant. A gage needs real oil. The thickness of the oil will
not effect the measurement ability of the gage. The oil will just
move out of the way, yet it will protect the surface of the gage
A fat thread will frequently cause the GO gage to fail
the thread. A marginally fat thread will be again close to the maximum
material condition and thus cause abrasion against the gage. A fat
thread is caused by too fast of a feed at the start of the thread
making process. The speed or feed causes either the work piece to
move away from the cutting tool, or the cutting tool to flex away
from the work piece, as the cut is begun. This condition needs to
be guarded against to avoid galling of the gage.
A fine pitch, larger diameter thread is a recipe for abrasion
of the thread gage. The more threads per inch the more revolutions
the gage makes to gain full engagement and thus a longer contact
distance for friction along the helical path of the thread.
The machining process may leave material chips in the threaded hole.
If these chips are not removed they may weld themselves to the gage
surface or get caught in the root of the gage thread. The fix for
this is simply to remove the chips. OK, it is not always simple
to remove them but it must be done to extend the life of the gage.
These are pieces of material still attached to the work piece but
protruding into the machined space left after cutting the thread.
Not removed they may weld themselves to the gage surface. If burrs
are a problem a different style cutting tool, a second pass with
the cutting tool, different speeds or feeds or just a wire brushing
may solve the problem.
Original Posted: 2/28/2008
Last Revised: 9/21/2011
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