Tap and a method of tapping

Abstract

The present invention provides a tap ( 10 ) adapted for formation of female screw-threads in a plurality of metal parts. Each female screw-thread is capable of imparting translational motion to a threaded second member engaged therewith, the threaded second member having a matching male screw-thread and the translational motion occurring on relative rotation between the first metal part and the threaded second member. The tap ( 10 ) is fluteless and comprises a threaded portion ( 23 ) with a triangular form thread ( 11 ) with an angle of thread (gamma) in the range 29° - 40 ° and radiussed crests ( 16 ). The present invention also relates to a method of using such a tap.

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       21 . A tap adapted for formation of female screw-threads in a plurality of metal parts, each female screw-thread being capable of imparting translational motion to a threaded second member engaged therewith, the threaded second member having a matching male screw-thread and the translational motion occurring on relative rotation between the first metal part and the threaded second member, the tap being fluteless and comprising a threaded portion with a symmetrical triangular form thread, wherein the symmetrical triangular form thread has an angle of thread in the range 29°-40° and radiussed crests. 
   
   
       22 . A tap as claimed in  claim 21  wherein the angle of thread is 29° to 31°. 
   
   
       23 . A tap as claimed in  claim 22  wherein the angle of thread is 30°. 
   
   
       24 . A tap as claimed in  claim 21  wherein the tap has a chamfered front end. 
   
   
       25 . A tap as claimed in  claim 24  wherein the chamfered front end extends over at least four turns of the thread. 
   
   
       26 . A tap as claimed in  claim 24  wherein the chamfered front end has a chamfer angle in the range 5.5° to 6.5°. 
   
   
       27 . A tap as claimed in  claim 21  which has at least two starts. 
   
   
       28 . A tap as claimed in  claim 21  wherein the thread has a pitch of 0.995 mm to 1.005 mm. 
   
   
       29 . A tap as claimed in  claim 21  comprising additionally lubrication grooves. 
   
   
       30 . A tap as claimed in  claim 21  comprising a shank portion extending rearwardly from the threaded portion and a rearmost portion with a plurality of flat surfaces to enable engagement of the tap by a chuck. 
   
   
       31 . A tap as claimed in  claim 30  in which at least one of the flat surfaces is precision machined in order to precisely set a distance between the front of the tap and at least one end of the flat surface. 
   
   
       32 . A product having a tapped bore with a female screw-thread flow formed using a fluteless tap comprising a threaded portion with a symmetrical triangular form thread, wherein the symmetrical triangular form thread has an angle of thread in the range 29°-40° and radiussed crests. 
   
   
       33 . A method of tapping a product comprising the steps of:
 forming a fluteless tap comprising a threaded portion with a symmetrical triangular form thread, wherein the symmetrical triangular form thread has an angle of thread in the range 29°-40° and radiussed crests; and   flow forming a female screw thread using the fluteless tap.   
   
   
       34 . A method of manufacture of apparatus which has a first metal object with a female screw-thread and a second metal object with a matching male screw-thread, the method comprising the steps of:
 forming a fluteless tap comprising a threaded portion with a symmetrical triangular form thread, wherein the symmetrical triangular form thread has an angle of thread in the range 29°-40° and radiussed crests;   forming in the first metal object a female screw-thread using the fluteless tap;   forming on at least a part of the second metal object a male screw-thread matching the female screw-thread of the first metal object;   engaging the male screw-thread of the second metal object with the female screw-thread of the first metal object; and   rotating one of the first and second metal objects relative to the other in order to occasion translational motion of the second metal object relative to the first metal object.   
   
   
       35 . A tap adapted for formation of female screw-threads in a plurality of metal parts, each female screw-thread being capable of imparting translational motion to a threaded second member engaged therewith, the threaded second member having a matching male screw-thread and the translational motion occurring on relative rotation between the first metal part and the threaded second member, the tap being fluteless and comprising a threaded portion with a symmetrical triangular form thread, wherein the symmetrical triangular form thread has an angle of thread in the range 29°-40° and radiussed crests and the tap has a chamfered front end. 
   
   
       36 . A tap as claimed in  claim 35  wherein the chamfered front end extends over at least four turns of the thread. 
   
   
       37 . A tap adapted for formation of female screw-threads in a plurality of metal parts, each female screw-thread being capable of imparting translational motion to a threaded second member engaged therewith, the threaded second member having a matching male screw-thread and the translational motion occurring on relative rotation between the first metal part and the threaded second member, the tap being fluteless and comprising a threaded portion with a symmetrical triangular form thread and at least two starts, wherein the symmetrical triangular form thread has an angle of thread in the range 29°-40° and radiussed crests.