WO1996004091A1

WO1996004091A1 - Self-chamfering drill bit

Info

Publication number: WO1996004091A1
Application number: PCT/CA1994/000429
Authority: WO
Inventors: Karl P. Schneider
Original assignee: Schneider Karl P
Priority date: 1994-08-05
Filing date: 1994-08-05
Publication date: 1996-02-15
Also published as: CA2196865C; CA2196865A1; AU7380494A

Abstract

A self-chamfering drill bit is disclosed having a shank (12) with a longitudinal groove (28) formed therein. A resilient, cantilevered insert (36) is located in the groove. The insert has a radially projecting cutting tip (44) formed thereon. The cutting tip has forward and rearward bevelled cutting edges (46, 48) formed thereon, so that as the drill advances to make a hole in a workpiece (60), the cutting tip forward bevelled cutting edge chamfers the front side of the hole. The cutting tip then retracts into the groove as it passes through the workpiece, and as the cutting tip emerges from the backside of the workpiece, the cutting tip rearward bevelled cutting edge automatically chamfers the backside of the hole being made in the workpiece.

Description

SELF-CHAMFERING DRILL BIT

TECHNICAL FIELDt

This invention relates to drill bits, and in particular, to drill bits that automatically chamfer a hole being drilled by the drill bit.

BACKGROUND ART;

It is often desirable where holes are drilled or formed in workpieces to countersink or chamfer the peripheral edge of the hole. Usually the hole is drilled and then a separate countersink is used to form the chamfer. Drill bits have been made in the past, however, where the countersink has been made an integral part of the drill bit. The countersink being spaced rearwardly or longitudinally back from the tip of the drill bit.

In some applications, where holes are drilled right through a workpiece, it is desirable to countersink the hole on both sides of the workpiece. Where a separate drill and countersink is used, three operations are necessary to complete the task. First, the hole is drilled, and then a second and third operation is necessary to countersink the hole on either side of the workpiece. If a combined drill and countersink is used, it is still necessary to perform two operations. First, the hole is drilled and countersunk on one side, and then the hole on the opposite side of the workpiece has to be countersunk in a separate operation.

DISCLOSURE OF THE INVENTION; The present invention is a self-chamfering drill bit that drills a hole and chamfers it on both sides of the workpiece with a single pass of the drill bit into and out of the workpiece.

According to one aspect of the invention, there is provided a εelf-chamfering drill bit comprising a shank having a forward, distal end portion including a pair of opposed, radially disposed cutting edges. The shank defines a longitudinal groove extending rearwardly from the distal end portion. The groove has a floor. A longitudinal insert is located in the groove. The insert has a forward end portion located adjacent to the shank distal end portion and spaced from the groove floor in its normal position. The insert also has a rearward end portion attached to the floor, so that the insert forward end portion can deflect radially inwardly from its normal position into the groove. A cutting tip is mounted on the insert forward end portion to project radially, outwardly from a shank and retract into the shank groove upon inward deflection of the insert. The tip has forward and rearward bevel cutting edges. Also, bias means is provided for returning insert to its normal position after being deflected radially inwardly.

BRIEF DESCRIPTION OF THE DRAWINGS;

Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is an elevational view of a preferred embodiment of a self-chamfering drill bit according to the present invention;

Figure 2 is an enlarged, exploded, perspective view of the drill bit shown in Figure 1; Figure 3 is an enlarged sectional view of a portion of the drill bit of Figure 1 taken along lines 3-3 of Figure

1?

Figure 4 is an elevational view of the drill bit of

Figure 1 shown entering a workpiece; Figure 5 is a view similar to Figure 4 showing the drill chamfering the hole on the front side of the workpiece;

Figure 6 is a view similar to Figures 4 and 5 showing the drill chamfering insert retracted into the drill shank as it passes through the workpiece;

Figure 7 is a view similar to Figures 4 to 6 showing the drill chamfering insert emerging from the backside of the workpiece and starting to form the chamfer on the backside of the hole;

Figure 8 is a view similar to Figures 4 to 7 showing the drill passed all the way through the workpiece with the chamfering insert in its normal position as shown in Figure 4; and

Figure 9 is a sectional view of a hole in a workpiece chamfered on both sides after the drill bit has been removed from the workpiece.

BEST MODE FOR CARRYING OUT THE INVENTION;

Referring firstly to Figures 1 and 2, a preferred embodiment of a self-chamfering drill bit is generally indicated by reference numeral 10. Drill bit 10 is a heavy duty drill bit of a type that is used to drill holes in the webs of steel railroad rails to allow these rails to be joined together by having bolts pass through steel plates spanning the joints between the rails on either side of the rail webs. The holes drilled in these rails are typically about 3 centimetres in diameter and 1.6 centimetres deep.

In the case of railway rails, it is necessary to chamfer the holes on either side of the rail webs in order to prevent stress cracks forming around the peripheral edges of the holes. Drill bit 10 allows the holes to be drilled and chamfered on both sides of the web in a single operation, as will be described further below.

Drill bit 10 includes a shank 12 having a forward portion 14 and a rearward portion 16. Rearward portion 16 includes a flat 18 and is adapted to be gripped by a chuck to turn drill bit 10. Forward portion 14 includes a forward, distal end portion 20 including a pair of opposed, radially disposed cutting edges 22 in the form of replaceable carbide inserts. Shank 12 is provided with internal passages 24 for the flow of cutting fluid or coolant, either liquid or air, through drill bit 10. Internal passages 24 communicate with outlets 26 strategically placed to distribute the coolant as needed. It will be apparent to those skilled in the art that many variations can be made in the drill bit as described thus far to suit the size of hole and type of material being drilled. Shank 12 includes a longitudinal groove 28 extending rearwardly from distal end portion 20. Groove 28 has a floor 30 with a raised rearward portion 32 on which is mounted a spring 34 and a longitudinal chamfering insert 36 in a cantilever fashion by means of a cap screw 38 and washer 40.

Insert 36 has a forward end portion 42 located adjacent to the shank distal end portion 20. Forward end portion 42 is spaced from groove floor 30 in its normal position by being mounted as a cantilever on floor rearward portion 32 as indicated in Figure 3.

Forward end portion 42 includes a carbide cutting tip 44 brazed or silver soldered thereto to project radially, outwardly from shank 12 as seen best in Figures 3 and 4 to 8. Cutting tip 44 has a forward bevelled cutting edge 46, a rearward bevelled cutting edge 48 and an intermediate, outer bearing surface 50 located between the forward and rearward bevelled cutting edges 46, 48. Cutting tip 44 bearing surface 50 has a transverse side edge portion 52 located between the forward and rearward bevelled cutting edges 46, 48. This side edge portion 52 is rounded or chamfered as seen best in Figure 3, the purpose of which will be described further below.

As seen best in Figure 2, the forward end portion 42 of insert 36 is bevelled and insert 36 has a transversely enlarged rearward end portion 54 having a hole 56 to accommodate cap screw 38. When the rearward end portion 54 is attached to floor rearward portion 32, the insert forward end portion 42 and cutting tip 44 can deflect radially inwardly from their normal positions into groove 28. In fact, cutting tip 44 retracts into groove 28 upon inward deflection of insert 36 until bearing surface 50 is flush with the outer surface of shank distal end portion 20, as seen best in Figure 6. Insert 36 is narrower than longitudinal groove 28 and off-set to one side of groove 28 as indicated in Figures 1 and 3 to allow cuttings to be flushed out from underneath the cantilevered insert 36 and spring 34 and for this purpose, one of the coolant outlets 26 communicates with groove 28. Insert 36 is formed of A.I.S.I. or S.A.E. 4140 alloy steel heat treated to a hardness of 46 to 47 Rockwell C.

Spring 34 is a rectangular plate spring attached to floor rearward portion 32 by cap screw 38 passing through a hole 58 in the rearward end of spring 34. Spring 34 extends below insert 36 in a cantilever fashion parallel to and in contact with insert 36. Spring 34 is formed of tempered spring steel having a hardness of between 48 and 51 Rockwell C. Spring 34 and to some extent insert 36 form bias means for returning insert 36 to its normal position as indicated in Figures 1, 3 to 5 and 8 after being deflected radially inwardly into groove 28 as indicated in Figure 6. In operation, referring next to Figures 4 through 9, drill bit 10 is shown in Figure 4 starting to enter a workpiece 60 which could be the web of a steel railway rail. As drill bit 10 progresses into workpiece 60, cutting tip 44 engages workpiece 60 and the forward bevelled cutting edge 46 of cutting tip 44 makes a first peripheral chamfer 62 on the hole 64 being drilled in workpiece 60. As drill bit 10 progresses further into workpiece 60, chamfer 62 begins to act as a cam and cutting tip 44 acts as a cam follower causing cutting tip 44 to deflect inwardly down into groove 28 and discontinue the cutting action of cutting tip 44.

As drill bit 10 progresses further into workpiece 60 as indicated in Figure 6, cutting tip 44 is fully forced into groove 28. The bearing surface 50 and especially chamfered side edge portion 52 of cutting tip 44 prevents cutting tip 44 from enlarging or scoring the inside surface of hole 64. When drill bit 10 advances completely through workpiece 60 and cutting tip 44 begins to emerge from hole 64 as indicated in Figure 7, the rearward bevelled cutting edge 48 begins cutting a chamfer 66 on the backside of hole 64. When drill bit 10 passes completely through workpiece 60 as indicated in Figure 8, the drill bit is withdrawn, and as cutting tip 44 again engages workpiece 60, chamfer 66 is completed. However, by stopping drill bit 10 and holding it in the position shown in Figure 7, chamfer 66 could be completely formed, as desired.

The cutting speed and feed of drill bit 10 when drilling through steel typically varies from about 450 to 1200 R.P.M. at a feed rate between 2.5 and 75 centimetres per minute, depending upon the type of coolant used and the size of cuttings or chips produced. It will be appreciated that a skilled person could adjust the cutting speed and feed rate to suit the particular application, as desired.

Having described preferred embodiments, it will be appreciated that various modifications could be made to the preferred embodiments described above. For example, the shape of cutting tip 44 could be changed and the cutting angles of forward and rearward bevelled cutting edges 46, 48 could be altered to change the angle and shape of chamfers 62, 66. The type of carbide used for cutting tip 44 would be chosen to suit the material being drilled. Also, the hardness and materials used for insert 36 and spring 34, as well as the type of spring 34 used, could be varied to suit the material being drilled, especially if softer materials such as aluminum are being drilled. More than one insert 36 could be used in any particular drill bit if necessary or if it is desirable to speed up the drilling operation. Also, the length of insert 36 and spring 34 could be adjusted to suit the size of drill or the material being drilled. Workpieces of all shapes and configurations can be drilled with drill bit 10.

It will be apparent to those skilled in the art that in light of the foregoing disclosure, many alterations and modifications are possible in the practice . of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A self-chambering drill bit comprising: a shank having a forward, distal end portion including a pair of opposed, radially disposed cutting edges; the shank defining a longitudinal groove extending rearwardly from the distal end portion, the groove having a floor; a longitudinal insert located in the groove, the insert having a forward end portion located adjacent to the shank distal end portion and spaced from the groove floor in its normal position, the bit also having a rearward end portion attached to the floor, so that the insert forward end portion can deflect radially inwardly from its normal position into the groove; a cutting tip mounted on the insert forward end portion to project radially, outwardly from the shank and retract into the shank groove upon inward deflection of the insert, the tip having forward and rearward bevelled cutting edges; and bias means for returning the insert to its normal position after being deflected radially inwardly.

2. A self-chamfering drill bit as claimed in claim 1 wherein the insert is formed of 4140 steel heat treated to a hardness of 46 to 47 Rockwell C.

3. A self-chamfering drill bit as claimed in claim 1 wherein the insert is a flat strip releaεably connected to the shank remote from the distal end portion to form a cantilever.

4. A self-chamfering drill bit as claimed in claim 3 wherein the insert is narrower than the longitudinal groove and offset to one side of the groove.

5. A self-chamfering drill bit as claimed in claim 1 wherein the cutting tip is carbide.

6. A εelf-chamfering drill bit as claimed in claim 1 wherein the cutting tip has an intermediate, outer bearing surface located between the forward and rearward bevelled cutting edges.

7. A self-chamfering drill bit as claimed in claim 1 wherein the bias means includes a rectangular plate spring attached to the floor below the insert rearward end portion to extend below the insert, the spring being formed of tempered spring steel having a hardness of between 48 and 51 Rockwell C.

8. A εelf-chamfering drill bit as claimed in claim 3 wherein the bias means includes a rectangular plate spring attached to the floor below the insert rearward end portion to extend below the insert in a cantilever fashion parallel and in contact with the inεert, the spring being formed of tempered spring steel having a hardnesε of between 48 and 51 Rockwell C.

9. A self-chamfering drill bit as claimed in claim 5 wherein the tip has a tranεverse side edge portion located between the forward and rearward bevelled cutting edges, said side edge portion being chamfered.

10. A self-chamfering drill bit as claimed in claim 6 wherein said bearing surface includes a rounded or chamfered leading edge portion.