802 BELL SYSTEM TECHNICAL JOURNAL 



which occurs as the reference mark on the gage stem disappears into the sleeve. 

 The object of the adjustment is to see that the elevation of the specimen to pick 

 up the minor load shall not be carried so far as to cause even a partial application 

 of the major load, which to make a proper test, must be applied only through the 

 release mechanism." 



'To Make the Index Lever Adjustment, if Necessary. — When the test piece is 

 elevated until it starts to pick up the major load, loosen the lock nut of the screw 

 through the index lever which carries at its lower end a small steel plate engaging 

 the ball on the penetrator shaft while using a small screw-driver to firmly hold the 

 screw until after the nut is loose. Then turn the screw very slightly and note 

 result on position of gage pointer which should be at B-60 to B-70 before reclamping 

 the screw with its lock nut." 



(c) Protection Against Vibration. — If the bench or table on which the Rockwell 

 tester is mounted is subject to vibration, such as felt in the vicinity of other machines, 

 the tester should be mounted on a metal plate on sponge rubber at least 1 in. thick 

 or on any type of mounting that will effectually eliminate vibration from the machine. 

 Otherwise the pointer will penetrate farther into the material than when such 

 vibrations are absent. 



Cushioning of Latch. — -If, when the operating handle is being returned to its 

 normal position, the latch operates with such a snap as to noticeably change the 

 position of the dial pointer, felt or rubber washers should be placed under the trip 

 button in order to cushion this blow. If this snap is severe, difference in reading 

 of several hardness numbers may result. 



Testing Methods 



3. The anvil used shall have a polished bearing surface for the material of about 

 ^ in. in diameter. It shall be hard enough so that no visible indentation is made 

 when the thinnest material is tested. 



Before using the machine it shall be operated several times on a piece of scrap 

 material in order to firmly settle the penetrator, anvil and moving parts of the 

 machine. This should be done every day before the machine is used. 



Make a reading on at least one of the standard test blocks. This need not be 

 done every day if it has been found that the machine does not change. 



The Rockwell ball should be replaced by a new one occasionally and the operator 

 should be on the lookout for any permanent deformation of the ball which will 

 ordinarily be indicated by high readings on the standard test blocks. 



When applying the minor load, the capstan screw should be turned up so that 

 the pointer stops at "O" with a maximum variation of ± five divisions. The 

 last movement of this screw must always be in such a direction as to elevate the 

 specimen. 



In applying the major load the operating handle shall be allowed to revolve 

 without interference until the major load is completely applied. This may be 

 observed in two ways, (1) when the pointer suddenly slows down, or (2) watching 

 the weight arm to see that it is completely free from the control of the dash pot. 

 When the major load has thus been completely applied, the operating handle shall 

 be immediately brought back to the latched position without waiting for it to com- 

 plete its revolution. This should be accomplished in less than two seconds after 

 the major load is completely applied. 



The test specimen shall be well supported to prevent errors due to the overhang 

 of the specimen. 



All tests shall be made upon one thickness of the material. 



APPENDIX II 



STANDARD TEST PROCEDURE FOR TENSION TESTING OF 

 THIN SHEET METALS 



General 



1. (a) These specifications cover general methods for testing the tensile strength 

 of thin sheet, strip and flat wire materials for use in the manufacture of telephone 

 apparatus. They shall form part of individual specifications covering sheet metals 

 for specific purposes whenever so provided in the individual specifications. 



