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H A R T N E S S S C R E W THRAD COMPARATOR
wrench, the metal is forced to flow SO that we get
practically a perfect fit. This is due to the accommo-
dating and friendly characteristic of the metal to flow
under stress.
While the flow of metal under stress tends to
equalize the distribution of burden over the whole
length of engagement of the threaded parts, it cannot
make up for all the large inequalities that are found
in errors of lead.
We know that under the stress of the wrench the
threads of mating parts are made to conform to each
other at the time they are first screwed up, and we also
know that, if the original thread forms were too far
from true lead and general required characteristics,
the burden comes heaviest on a few of the threads
at one end of the engaging surface. These threads are
then overstressed, and to the extent that this improves
the fit it is friendly, but the friendly role ceases and the
trouble begins, if, after a screw has been set up, the flow
continues, especially when the stress of work is added
to the wrench stress. For then there is a gradual
yielding. This continued flow results in a change
of position of an adjusting screw or a loosening of a
fastening screw.
It is this obscure yielding that is SO troublesome
in the operation of machinery. It has always been the
bane of the machine user, whether he has been one who
risked his life in the use of the machine or his success
in his work or his business.
In order to minimize this trouble we must adopt
methods of measurement of screw threads in process
of production and in inspection which will tell us the
essential facts. Methods that show the resultant
effect of all the variants on the essential question of
dependability.
II
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": "H A R T N E S S S C R E W THRAD COMPARATOR\nwrench, the metal is forced to flow SO that we get\npractically a perfect fit. This is due to the accommo-\ndating and friendly characteristic of the metal to flow\nunder stress.\nWhile the flow of metal under stress tends to\nequalize the distribution of burden over the whole\nlength of engagement of the threaded parts, it cannot\nmake up for all the large inequalities that are found\nin errors of lead.\nWe know that under the stress of the wrench the\nthreads of mating parts are made to conform to each\nother at the time they are first screwed up, and we also\nknow that, if the original thread forms were too far\nfrom true lead and general required characteristics,\nthe burden comes heaviest on a few of the threads\nat one end of the engaging surface. These threads are\nthen overstressed, and to the extent that this improves\nthe fit it is friendly, but the friendly role ceases and the\ntrouble begins, if, after a screw has been set up, the flow\ncontinues, especially when the stress of work is added\nto the wrench stress. For then there is a gradual\nyielding. This continued flow results in a change\nof position of an adjusting screw or a loosening of a\nfastening screw.\nIt is this obscure yielding that is SO troublesome\nin the operation of machinery. It has always been the\nbane of the machine user, whether he has been one who\nrisked his life in the use of the machine or his success\nin his work or his business.\nIn order to minimize this trouble we must adopt\nmethods of measurement of screw threads in process\nof production and in inspection which will tell us the\nessential facts. Methods that show the resultant\neffect of all the variants on the essential question of\ndependability.\nII"
}