Патент USA US2114448код для вставки
April 19, 1938. Q. E. KOEHLER ET‘ AL~ 2,114,448 TAP Filed Nov. 10,1956 _ Patented Apr. 19, 1938 2,114,443 UNITED fsrAres PATENT. rice _, 2,114,448 TAP "(Oscar E. Koehler and Earl R. Koonz, Green?eld, ' Mass., assignors to Green?eld‘ Tap and Die Corporation, Green?eld, Mass, a corporation ofMassachusetts . Application November 10, 1936, Serial No. 110,063 1 Claims. - (01. 10-441) This invention relates to taps and more espe cially to taps having relatively wide lands. When holes to be threaded have key-ways or slots, the lands of the tap used obviously must be 5 wide enough to span the key-way or slot, and when the tap is of large diameter, wide lands are necessary to hold it in‘ position and prevent chat tering while the thread is being cut.v It has been found, however, that excessive friction is devel 10 oped in using such taps ‘and various expedients have been proposed for reducing it. ' ' A conventional solution of this problem is to “relieve” the thread by progressively deepening and widening the grooves between'the threads 1 GI from or near the cutting edge to the heel of each tween the cutting edges l8 and the heels l9 and converting the arc of the root of the thread into substantially a chord 20, as shown more clearly inFig;4'. 5‘ 1' " ' . ’ _ , Inv most cases, su?icient “relief” is obtained by merely reducing the width of flat portions 2| of‘ the threads without cutting them away entirely, so that thecrestx 22 of the threads remains ‘con centric and there is no substantial reduction of thread diameter even at the centerpofvthe land re where the_“relief” is‘a maximum. At both the cutting edge and the heel the cross section of thread is unchanged, as' shown in Fig. 5, but at the centerv of the relieved'portion the ?anks of the threads will assume the’ shape indicated by " land. While this procedure is effective in reduc ing the friction, it is found'when'the' rotation of the tap is reversed to remove it from the hole, the dotted line 23. Alternately, the relieved area may be of the that chips often lodge in the “relieved” or re at the root of thejthread is converted into a 20 cessed portions of the lands and are dragged into the threads which have just been cut, thereby impairing or completely destroying the ?nished work. The object of this invention is a tap of simple and inexpensive construction which is capable of cutting a clean thread without excessive friction, and which may be readily removed without in jury to the work. We have found that the friction is minimized 30 by a special reduction of the central portion of the lands, leaving both the heel and the cutting edge at full pitch diameter. This gives the de sired relief and at the same time avoids objec tionable wedging on reversal because chips can ' not enter the “relieved” portion during the re verse motion of the tap. In the drawing, Fig. 1 is a perspective view of a tap according to this invention. 40 Fig. 2 is an enlarged cross-sectional view of the tap showing the “relieved” portion of the lands. Fig. 3 is a plan view of a portion of one of the “relieved” lands. Fig. 4 is a sectional view of the land along the ' root of the threads shown in Fig. 3. Fig. 5 is an end view of the portion of the land shown in Fig. 3, and Figs. 6 and '7 show a “relieved” land of an al ternate construction. 50 The tap of Fig. 1 comprises a shank II with a plurality of threaded lands l2 separated by ?utes l3 and tapered at the end [4 in the usual man ner. The section in Fig. 2 taken at the root i5 of the thread shows the “relieved” portions l6 ex 55 tending over the central parts of the lands be shape shown inll‘ig. '7, in which the convex'arc slightlyconcavev are 24', but asin the previous case‘the'?ats 2| of the thread are preferably not reduced beyond the point where the crests come to a sharp edge 25 of full pitch diameter. In making the tap of this invention, the grind ing wheel is set to grind the lands on the cor rect pitch diameter and is then given a prede 25 termined inward shift cutting into the root cir cle as the wheel approaches and recedes from the center of each successive land so as to relatively reduce the ?anks over the central part of the 30 lands and convert the are at the root of the thread to a chord or to a concave are as the case may be. Or the threads may be ground in usual manner and the grinding wheel passed through the thread in separate operation, giving the de sired cutting action at the centers of the lands. The type of relief shown in Figs. 6 and 7 may be obtained by rotating the tap intermittently and moving the grinding wheel 26 radially of the tap into the groove between the threads to the 40 position shown in Fig. 7 while the tap is at rest. The wheel is then retracted beyond the root cir c-le 21 and the tap is rotated to bring the next land into grinding position. This procedure is repeated until the tap is relieved throughout the full length (or any desired portion) of the thread, it being understood that the wheel is being con tinuously advanced under the control of the lead screw, as in the ordinary grinding operation. Other methods of grinding this chordal type of relief will be obvious and will vary in the shapes of the parts ground away and in the conforma tion of the bottom surface of the groove, the lat ter being either concave as shown in Figs. 4 and 55 2 2,1 14,448 7 or substantially ?at or convex, depending upon the particular method used. The tap of this invention lends itself readily to accurate formation during the grinding of the tap threads, the grinding tool simply being moved both the cutting edge and the heel toward the center of the land. 3. A tap having threaded lands separated by flutes de?ning cutting edges and heels on the lands, and with threads on each land having in termediate portions diminishing in width from both the cutting edge and the heel toward the center of the land while maintaining the apexes of said threads undiminished in height. 4. A tap having threaded lands separated by 10 with relation to the threads to give the desired relief. The resulting construction preserves the full thread formation at each end of the land and at the same time obviates the objectionable fric 10 tional drag and substitutes for this a helpful ?utes de?ning cutting edges and heels on the distribution of the lubricating oil. The central portions of the lands cut away in accordance with lands and with threads on each land diminished this invention provide extended shallow pockets in width at intermediate portions between the cutting edge andthe heel, the grooves between on each side of each thread catching the lubri the threads being deepened adjacent the inter 15 15 cating oil and carrying it and spreading it over mediate thinner portions of the threads. the freshly-cut surfaces of the threads as they 5. A tap having threaded lands separated by are formed by the tap. This relieving of the cen flutes de?ning cutting edges and heels on the tral portions also maintains the strength and ri gidity of the threads and preserves an accurately lands, and with threads on each land having in > termediate portions ground to diminished width 20 20 centered continuous connection between the cut ting and trailing portions so that the full strength from both the cutting edge and the heel toward of the entire thread is available in support of the the center of the land while maintaining the apexes of said threads undiminished in height. cutting edge in each direction.‘ While this invention has been described in con 25 nection with speci?c embodiments, it is not lim ited thereto. Other methods of providing the relief may be used and cam control of the grind ing wheel may be employed to give any desired form to the out including, for instance, a precise 30 ly straight lined chord 20 at the root of the relief. We claim: ' 1. A tap having threaded lands separated by ?utes de?ning cutting edges and heels on the lands, the threads on a portion of each land hav 35 ing crests diminishing in width from both the cutting edge and the heel toward the center of the land. 2. A tap having threaded lands separated by ?utes de?ning cutting edges and heels on the 40 lands, and with threads on each land having in termediate portions diminishing in width from 6. A tap having’threaded lands separated by ?utes de?ning cutting edges and heels on the 25 lands, and with threads on each land ground to diminished width at intermediate portions be tween the cutting' edge and the heel, the grooves between the threads being deepened adjacent the intermediate thinner portions of the threads. 30 7. A tap having threaded lands separated by ?utes de?ning cutting edges and heels on the lands, and with threads on each land ground to diminished width at intermediate portions be tween the cutting edge and the heel, the grooves 35 between the threads being deepened on lines of concave curvature adjacent the intermediate thinner portions of the threads. ‘OSCAR E. KOEHLER. EARL R. KOONZ.