Study of a Tapping Method for Large Size Threads. (3rd Report). Consideration for the Roughness of Thread Surface by Tapping.

This paper describes the roughness of flank surface by tapping for a large size threads with a geometrical analysis and experiments. The behavior of roughness is experimentally studied by the turning test using the imitated cutting edges and every variety of cutting oils and the tapping test using M 42×4.5 tap. The results are as follows. (1) The roughness of flank surface is affected by the depth of cut per one cutting edge in tapping. It becomes small as the cutting depth is finer. (2) There are three effective methods to make the cutting depth thin, that is, to select smaller pitch thread, to make the chamfer angle small by reducing a percentage of thread engagement, and to increase the number of tap grooves. (3) In order to improve the roughness of flank, it is effective to use the lower effervescent oil and the slower tapping speed. (4) The excellence of soy sauce as the cutting oil for tapping was revealed through the cutting test. However, the rate of salt and stink are questionable so that it is necessary to develop a new tapping oil containing the lower effervescent oil. (5) If the cutting edge of a current manufactured tap is sharpened the sweep edge on a whetstone, the roughness of flank surface can be improved.