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HARTNESS
SCREW THRED COMPARATOR
SUMMARY
E HAVE shown that the common
G
0
practice of screw thread measure-
ment does not reveal the essential
W
characteristics of the thread. Since
it does not show us the extent of
the thread surface that will be in
contact with a normal mating part,
it neither tells us the dependability of the screw as a
holding means nor its wearing qualities when sub-
jected to frequent adjustment.
The photographs of thread profiles show that the
screw threads are not true to form that the so-called
cutting process is in reality a crushing and extruding
process by which the tooth form of the cutter becomes
a plow on which there adheres a variable pile of metal.
This crushing, pushing, extruding process merely
gets the screw ready for the real finishing process,
which is squeezing the thread into conformation with
its mate-the nut or threaded hole.
The essential work that the die is to accomplish
is to bring the thread into a form that is as near to the
standard as the manufacture processes and the charac-
ter of the service demand.
We know that by taking special care and ample
time we can make nicely formed screws-screws hav-
ing form, surface and lead that appear satisfactory to
the keen, highly developed vision of the experienced
worker-but we also know that a magnification of such
thread frequently reveals undesirable irregularities.
But in ninety per cent of the work the manufac-
turing conditions do not permit such special care, and
we are forced to produce screws that under magnifica-
tion are shown to possess irregularities that make the
38
Document source description
This is a publication about a comparator machine for the inspection of screw threads, with illustrations by Russell W. Porter.
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"ocrText": "HARTNESS\nSCREW THRED COMPARATOR\nSUMMARY\nE HAVE shown that the common\nG\n0\npractice of screw thread measure-\nment does not reveal the essential\nW\ncharacteristics of the thread. Since\nit does not show us the extent of\nthe thread surface that will be in\ncontact with a normal mating part,\nit neither tells us the dependability of the screw as a\nholding means nor its wearing qualities when sub-\njected to frequent adjustment.\nThe photographs of thread profiles show that the\nscrew threads are not true to form that the so-called\ncutting process is in reality a crushing and extruding\nprocess by which the tooth form of the cutter becomes\na plow on which there adheres a variable pile of metal.\nThis crushing, pushing, extruding process merely\ngets the screw ready for the real finishing process,\nwhich is squeezing the thread into conformation with\nits mate-the nut or threaded hole.\nThe essential work that the die is to accomplish\nis to bring the thread into a form that is as near to the\nstandard as the manufacture processes and the charac-\nter of the service demand.\nWe know that by taking special care and ample\ntime we can make nicely formed screws-screws hav-\ning form, surface and lead that appear satisfactory to\nthe keen, highly developed vision of the experienced\nworker-but we also know that a magnification of such\nthread frequently reveals undesirable irregularities.\nBut in ninety per cent of the work the manufac-\nturing conditions do not permit such special care, and\nwe are forced to produce screws that under magnifica-\ntion are shown to possess irregularities that make the\n38"
}