US 2328629 A
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Patentecl Sept. 7, 1943 Fra nk A. Eich, Melrose, Mass., am! Frank E. Higg1ns, 1'laistow, N. H. assignors to United Shoe Machmery Corporation, Flemington, N. J., a corpora.tion of New Jersey Original application July 29, 1940, Seria1 N0.
- 348,090. Divided und this 4, 1941, Seria.l N0. 373,156
Heretofore, it has been diflicult rapidly and easily to drill hard wood, such as maple. with a twist drill of the usual type because the dril1 would not readily penetrate the work but would become overheated, which would draw its temper, and burn the wood. Accordingly, it has been necessary to use for th is work a drill which has a sharp pyramidal center point and small circumferential lips which cut and define the outer Wall 01' the bottom of the drilled hole before the chips are shaved of1 and removed from that part of the hole by the body of the drill. While such drills are suitable for this work, they must be kept sharp by frequent and difficulthand grinding in order to maintain them in proper working condition.
It is an object of the present invention 120 provide a multi-fluted, and preferably a, doublefiuted, twist dri1l with a point somewhat similar to the usual form of twist drill point but which is especially shaped to penetrate hard wood without exoessive heating. Such a drill may be sharpened conveniently and accurately on a grinding machine which has been specially developed for the purp0se by the present inventors, which machine is described and claimed in an application for Letters Patent of the United States, Seria1 N0. 348,090, filed July 29, 1940, of which application the present application is a division.
The various features of the dril1 consist of end surfaces cf novel shape arranged to meet in a nove1 manner to form cutting edges and cleararmes suitable for the intended c1ass of work.
One of these features eliminates the usual chisel edge tha'b is regularly formal across the web of a dril1 at 90 to its axis. 'Ihis is especially important as such an edge impedes the penetration Of the dri1l and sorapes er tears the fibres of the wood in the center of the hole being drilled. For such an edge, there is substituted one which is in two portions, each of which makes an angle of 1ess than 90 to the axis of the drill, and together provide an edged web which is inclined to the surface being drilled and easily penetrates the work. v
The end of the dri11 is diametrically symmetrical and consists of four irregularly shapeddiscontinuous faces meeting in a common point a.t substantially the geometric center of the drill.
Referring to the drawing,
.Fig. 1 is an enlarged erid view of the drill of the present invention;
Fig. 2 is an enlarged e1evation of the dr111 100king in the direction of the arrow A in Fig. 1; a.nd
application January Fig. 3 is an enlarged view 0fthe drill, looking in the directlon cf the arrow Bin F1g. 1.
As illustrated, the preferred form of drill o! the present invention is a right-hand, doublefiuted twist dri1l M so that. when operating to.
dri1l a hole, it rotates in the direction of the arrow in Fig. 1. It is provided with a nove1 end which makes it possible to drill hard wand et high .speed without drawing the temper of the drill or burning the wood. In Fig. 1 the fiutes for slight clearance) in the surface of a cone 013 approximately included angle (see Flg. 3) and the wider concave clearance surfaces 20 and 20'. The surfaces 20 and 20' are locatad behind the1r respective lands and extend to substantially the geometric center of the drill, cutting into the web of the drill. Each 1and and the concave clearance surface in front of lt meet to form a cutting ede on the web at one side of the center of the dri1l (i. e., I8' meeting with 20 and 18 with 20'), as indicated at 22 and 22' on what will be termed the forward edf;e of each 1and. The two parts of the cutting edg'e thus formed appear, in end view, to extend across the web of the drill in substantially -a straight line.
The remaining portion of each cutting edge as indicated at 24 and 24', continues in a. curve a1: a. considerable angle to the Just-described portions 22 and 22', until it ends at the circumference of the drill. 'I'hls part of each edge is formed by the meeting of the remalning portion of the forward edge of each 1and and the flute immediately in front of the same (1. e. 18 w1th I6 a.nd I8 with Hi). The straight and curved portlons of each edge together recede (1. e., extend. clockwise in Fig. 1) from the center of the drill substantially before reaching its circumference. In other words the direction of the edge, when seen in end view, varies through substantially 90 from the center to the perlphen? of the dr1ll.
Ea.ch concave clearance surface provldes a. pa.th for guiding the chips to the adjacent flute, through which they pass from the work.
It should be noted tha.t each concave clearance surface extends substantiallxr to the center of the drill, each such surface cutting away a portlon of the web but so related that suflicient metal remains on the web to support ea.ch entt1ng edge. The short or central portlons 22 und 22' o! the cuttlng edge. l. e., those on the web. lle in a. substantlalJy-contlnuous axlal plane. (However, the ed8e cannqt lle exactly in such a plane es 1tis practlcally imposslble to ha.ve the edges meet in exa.ct allnement at an exa.ct polnt at the geometrlc center of the drlll, elthough In fact. each edze is ofiset from the center by only a. few thousandths o! an inch et the most. 'I'hls oflset ma.y be consldered in. efl!ect es a. sllght web 01 thls dimenslon. Accordingly, although the drlll o! the present invention possesses e, web havlng the strerigth 015 the usual drlll, 112 posses'ses only a slight web at the pe11etratin p01nt whose thickness is practically nfl.)
When viewed a1: rlsht angles to thls axla.l plane.
these edze portlons slant away from the centerof the drll1 to leave a polnt. The rema.lning portlons 24 and 24' 01 the two cuttlng edges are tormed on the forward edge 015 euch land und. therefore, thls portlon of each cuttlng edge is much steeper than the portlon l.ving on the web because lt lies in the 60 cone 015 Fig. 3. It is therefore evident that all parts of ea.ch cutting edge slam; or taper from the periphery to the axls of the drill to form a polnt; and because of this construction the drill will easlly penetrate ha.rd 01' other wood. In other words, the drlll does not have the usual chlsel edge that lies at rlght angles to the axis o1 the drill und which,
concave clearance surface behind the land und wlthln sa.id cone, all cf sa.ld surfacea 01 all ot. the llps meetlng at substantlally the geometrlc center o! the drlll.
2. A double-lipped twlst drlll, ea.ch l1p havlng two irregularly-shaped dlscontinuous surfaces, one cf which :ls a narrow land, and the other 01 whlch -ls a wider conca.ve clearance surlace behlnd the land, all 01' sald surfaces meetlng at substantlally the geometrlc center of the drlll.
3. A. double-llpped twlst drlll, each lip havin: two lrregularly-shaped dlscontlnuous surfaees. one ot whlch ls a land, und the other 01 whlch ls e. concave clearance surface behlnd the land, both o! seid surfaces meetlng at substantlally the geometrle center cf the drll1 und the land lylnz in the surfs.ce 015 a cone havlng an lncluded angle of substantlally 4. A twlst drill heving a plurallty of simllar llps spaced equally around the axis 01 the drlll, the llps haVing cuttlng edges whlch taper from the periphery ofthe drill to the axis to Iorm a point, a major portion o! euch edge belng curved in end view a.nd a minor portion belng stralght, and seid straight portlons me eting at sa1d point.
5. A twlst drlll having a plurallty o1 similar lips spaced equally around the axis cf the drlll. 4
the lips ha.ving cutting edges which taper trom the periphery of the drll1 to the a.xl to form a polnt. a major portion 01 euch edge being curved ln'end view and a, minor portlon beim; straight, seid straight pqrtions meeting ab seid point, and the dlrection of each edge, when seen in end vlew, varylng through substantially from the center to the perlphery of the drill.
FRANK A. EICH. FRANK E. HIGGINS.