Guide Pad Mounting On A Drill Bit

Abstract

A drill has a guide pad pivotally mounted on it, on that the guide pad may adapt itself to the surface of a hole wherein the drill is being operated.

Description

The present invention relates to a drill having one or more guide pads which support and guide the drill within the drill hole. It is previously known to attach such pads rigidly to the drill and adapt them to match the drill hole, so that there is established a full contact between the outer surface of the pad and the wall of the hole. Now it has been observed that the shape of the drill may change, for instance by elastic deformation or by diameter wear, in such a way that there is established only a partial contact between the pads and the wall of the hole. This results in an increased specific surface pressure from the pads causing undue friction.

The invention provides an improvement in this regard by means of a guide pad which is mounted on a pivot, so that it can rock and adapt itself to the surface of the hole, thereby securing a full surface contact.

The invention is closer described in the following specification with appended drawings, showing:

FIG. 1, a side view of a drill according to the invention.

FIG. 2, an end view of the same drill.

FIG. 3, a guide pad on the same drill.

FIG. 4, a cross section on the line 4--4 in FIG. 3.

FIG. 5, a side view of another embodiment of the invention.

FIG. 6, an end view of the drill in FIG. 5.

FIG. 7, a side view of a third embodiment of the invention.

FIG. 8, an end view of the drill in FIG. 7.

The drill 10 shown in FIGS. 1 and 2 is a metal drill having a number of cutting inserts 11 clamped in supports 13 by clamps 12 of which all except one have been omitted in FIG. 2. The supports 13 are attached to the drill in a suitable way, e.g., by screws or by brazing.

For supporting and guiding the drill in the hole are provided two guide pads 20, suitably of sintered carbide. The pads are mounted on a pivot so that they can rock around both a longitudinal and a transverse axis. The pivoting around a longitudinal axis is obtained by means of a support 21 with a cylindrical sliding surface 22, which rests on a matching surface 23 in a depression in the drill. The periphery surface 25 of the support 21 is approximately flush with the periphery surface of the drill. The support is fastened with a screw 26 (FIG. 1) and a resilient washer 27 permitting rocking of the support.

The pivot axis 24 lies outside the pad in order that when the drill rotates the friction on the pad will urge the leading edge 28 of the pad away from the edge of the hole. This lessens the friction and facilitates the entering of the lubricant between the pad and the wall. By a suitable position of the centre 24 the surface pressure can be properly distributed with regard to the hydrodynamic effect of the lubricant.

The pivoting on a transverse axis is obtained by a support 30 having a cylindrical surface 31 sliding along a matching surface 32 in the support 21. The pad is held by a tubular pin 34 within a bore through both supports 21 and 30. As the axis of the pin lies outside the pivot centre 33, the rocking requires bending of the pin. This is made possible by an annular space 35 extending along a part of the pin 34.

The pivot mounting around two perpendicular axii provided by the above described two cylindrical sliding joints may be obtained by a single spherical joint.

FIGS. 5 and 6 show a modified embodiment of the invention in which the pad unit 40 is symmetrical. It carries two sintered carbide pads 41 on each side of a fastening screw 42, under the head of which there is a helical spring 43 permitting the rocking around a longitudinal axis. This embodiment comprises no rocking on a transverse axis. The advantage of the symmetrical pad is that the pad can be turned half a turn when it has been worn out on the side having the greatest pressure.

FIGS. 7 and 8 show another symmetrical pad unit 50 having four pad inserts 51 on a drill for counterboring (reaming), i.e. for enlarging the internal diameter of holes. The specific advantage is that the great area of the pads makes the tool suitable for reaming the inner diameter of tubes with a thin wall that would be damaged by the pressure from smaller guide pads.

Claims

I claim:

1. Drill for drilling in metal having a guide pad adapted to slide with frictional contact along the wall of the drill hole, in which the guide pad is pivotally rockable on at least one axis having the same general direction as the sliding surface of the guide pad and situated at a fixed distance from the drill axis.

2. Drill as defined in claim 1, in which the guide pad is mounted on a sliding bearing with a curved sliding bearing surface.

3. Drill as defined in claim 1 in which the pivot comprises a cylindrical sliding bearing with a longitudinal axis.

4. Drill as defined in claim 3, in which the pivot comprises a second cylindrical sliding bearing with a transverse axis.

5. Drill as defined in claim 1 in which the pivot comprises a spherical sliding bearing.

6. Drill as defined in claim 1 having a guide pad on a longitudinal pivot axis, in which said axis lies outside the periphery surface of the pad.

7. Drill as defined in claim 1, in which the pivoted guide pad is rockable about longitudinal and transverse axes whereby said guide pad adapts itself to the surface of a hole in which said drill is being operated.