GB2157206A - Hole cutter - Google Patents

Abstract

The hole cutter has a generally cylindrical cutter body 21 provided around its lower end with a plurality of first cutting teeth 23 each having a plurality of cutting edges 25, 26, and a plurality of second cutting teeth 24 adapted to scrape a surface cut by the first cutting teeth 23. <IMAGE>

Description

SPECIFICATION Hole cutter This invention relates to a hole cutter having a plurality of cutting teeth provided around the lower end of a generally cylindrical cutter body.

What is desired is a hole cutter having a high chip ejection efficiency and a high hole cutting efficiency with a reduced cutting resistance. It is also desirable to provide a hole cutter which is very easy to sharpen.

The invention provides a hole cutter having a plurality of cutting teeth provided around the lower end of a generally cylindrical cutter body, the cutting teeth comprising a plurality of first cutting teeth each having a plurality of cutting edges and a plurality of second cutting teeth adapted to scrape the surface cut by the first cutting teeth. The first and second cutting teeth are preferably located alternately with each other.

In a preferred embodiment, each of the first cutting teeth has clearance faces defining a clearance angle and cutting angles which are substantially equal to the corresponding angles defined by clearance faces on the second cutting teeth. Each first cutting tooth has a stepped front face defining a plurality of cutting edges, and each second cutting tooth has a smaller number of cutting edges than each first cutting tooth. The first and second cutting teeth have a substantially equal rake angle.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a front elevational view of a hole cutter; Figure 2 is a fragmentary perspective view showing the arrangement of cutting teeth Figure 3 is a fragmentary enlarged perspective view showing a first cutting tooth and a second cutting tooth; Figure 4 is a bottom plan view of the hole cutter; Figure 5 is a fragmentary side elevational view showing a clearance face on a first cutting tooth; Figure 6 is a fragmentary side elevational view showing a cleanrance face on a second cutting tooth; Figure 7 is a fragmentary front elevational view showing cutting edges on a first cutting tooth; Figure 8 is a fragmentary front elevational view showing a cutting edge on a second cutting tooth;; Figures 9 to 11 are a series of enlarged sectional views showing a number of cutting teeth in successive use for the cutting operation; and Figure 12 is a view illustrating a mode of chip ejection.

The hole cutter illustrated includes a generally cylindrical cutter body 21 provided at its upper end with an upright shank 22 by which the cutter is connected to a rotary shaft (not shown). The cutter body 21 is provided around its lower end with a plurality of first cutting teeth 23 and a plurality of second cutting teeth 24 which are located in equally spaced, alternate relation with each other.

The bottom surface of each of the cutting teeth 23 and 24 has a crest 29 which divides an inner clearance face 38, as shown in Figures 2 and 4. The crests 29 of the cutting teeth 23 and 24 define a substantially equal clearance angle ot, as shown in Figures 5 and 6. Accordingly, the clearance faces 37 and 38 of the cutting teeth 23 and 24 also have a substantially equal clearance angle . The crests 29 of the cutting teeth 23 and 24 are located substantially on the circumference of a circle having its centre on the longitudinal axis of the cutter.

Each of the first cutting teeth 23 has a stepped front face defining an inner cutting edge 25, an outer cutting edge 26, and a should 27 located between, as shown in Figures 2 to 5. The outer cutting edge 26 is divided by the front end of the crest 29 into an inner cutting edge portion 30 and an outer cutting edge portion 31. Each of the second cutting teeth 24 has a cutting edge 28 which is divided by the front end of the crest 29 into an inner cutting edge portion 32 and an outer cutting edge portion 33.

The inner clearance faces 37 of the cutting teeth 23 and 24 have an equal cutting angle ss to the rotating plane of the hole cutter,and their outer clearance faces 38 also have an equal cutting angle y thereto. Therefore, the inner cutting edge 25 and inner cutting edge portion 30 of each first cutting tooth 23 and the inner cutting edge portion 32 of each second cutting tooth 24 have an equal cutting angle ss, and the outer cutting edge portions 31 and 33 of the cutting teeth 23 and 24, respectively, have an equal cutting angle y, as shown in Figures 7 and 8. The apexes of the cutting teeth 23 and 24 defined at the front ends of the crests 29 are located substantially on the circumference of a circle having its centre on the axis of rotation of the hole cutter.The apexes of the second cutting teeth 24 are, however, slightly spaced above those of the first cutting teeth 23. The cutting teeth 23 and 24 have an equal rake angle 5, as is obvious from Figures 5 and 6.

The cutter body 21 is provided on its outer periphery with a ridge 34 spirally upwardly extending from each of the cutting teeth 23 and 24. Every two adjoining ridges 34 define a flute 35 for chip ejection between them. The cutter body 21 is also formed at its lower end with a gullet 36 for chip ejection which is located between every two adjoining cutting teeth 23 and 24.

In operation, each first cutting tooth 23 cuts the material 42 to be cut to form two cut surfaces 39 and 40 by the inner and outer cutting edges 25 and 26, respectively, as shown in Figure 9. Then, each second cutting tooth 24 cuts only the outer cut surface 40 formed by the outer cutting edge 26 of the first cutting tooth 23, as shown in Figure 10. This reduces the difference in height between the inner and outer cut surfaces 39 and 40, and the inner and outer cutting edges 25 and 26 of another first cutting tooth 23 cut chips of different thickness.

Therefore, the inner and outer chips are of different rigidity, and have different angles e of ejection, as is obvious from Figure 12.

If the inner and outer chips were equal in thickness, they would have an equal angle of ejection, and would undergo plastic deformation to form a single chip even if the inner and outer cutting edges 25 and 26 were spaced apart from each other circumferentially or vertically. The chip having a greater width would be difficult to eject, and would have an adverse effect on the working efficiency of the hole cutter.

The hole cutter, however, produces only chips which are narrow enough to be easily ejected. The chip cut by the outer cutting edge 26 is so thick and rigid that it is ejected with the chip cut by the inner cutting edge 25 which is thinner and would otherwise be likely to stick to the tooth. Thus, both the inner and outer chips are easy to eject. The clearance between the inner cutting edge portion 32 of the second cutting tooth 24 and the cut surface 39 is so small, as shown in Figure 10, that any chip remaining on the cut surface 39 is scraped away by the inner cutting edge portion 32. This ensures satisfactory cutting of the surface 39 by another first cutting tooth 23. Thus, the hole cutter enables a high chip ejection efficiency and thereby a high cutting efficiency.

The crests 29 of the first and second cutting teeth 23 and 24 are located substantially on the circumference of a single circle, and their clearance faces 37 and 38 define substantially equal clearance angles and cutting angles a and ss, as stated above. This means that the clearance faces 37 and 38 of the cutting teeth 23 and 24 face substantially in the same direction, rendering their sharpening very easy.

Although the invention has been described with reference to a preferred embodiment thereof, it is, of course, a mere example, thereof, and the invention may be employed in various other modes as will be set forth below by way of example.

(1) A plurality of cutter tips which are separate from the cutter body and formed each with one of the first and second cutting teeth may be secured by brazing or otherwise to the lower end of the cutter body.

(2) It is possible to locate the first cutting teeth 23 in pairs and to dispose a second cutting tooth 24 between every two adjoining pairs of first cutting teeth 23, instead of positioning the first and second cutting teeth exactly alternately with each other as shown in the drawings. In this case, however, it is desirable to dispose teeth of the same type at the diametrically opposite positions of the cutter.

(3) The cutting teeth may be of the type free from any crest and, therefore, having only a single clearance face.

Claims (5)

1. A hole cutter having a plurality of cutting teeth provided around the lower end of a generally cylindrical cutter body, the cutting teeth comprising a plurality of first cutting teeth each having a plurality of cutting edges, and a plurality of second cutting teeth adapted to scrape a surface cut by the first cutting teeth.

2. A hole cutter as claimed in claim 1, in which the first and second cutting teeth are disposed alternately with each other.

3. A hole cutter as claimed in claim 1 or 2, in which each first cutting tooth has two clearance faces defining a clearance angle and two cutting angles which are substantially equal to the corresponding angles defined by two clearance faces on each second cutting tooth, and has a stepped front face defining the said cutting edges, the second cutting teeth each having a smaller number od cutting edges than the first cutting teeth.

4. A hole cutter as claimed in any preceding claim, in which the first and second cutting teeth have a substantially equal rake angle.

5. A hole cutter substantially as described with reference to, and as shown in, the accompanying drawings.