GB2232619A - Annular cutter - Google Patents

Abstract

The cutter has a generally cylindrical hollow main tool body and drive connection means at one end. Cutting means at the other end has a plurality of spaced teeth defining cutting edges including inner and outer cutting edges. Each tooth has only an inner cutting edge or an outer cutting edge. For each tooth A having an outer cutting edge the portion corresponding to the inner cutting edge is at least partially removed, and for each tooth having an inner cutting edge, the portion corresponding to the outer cutting edge is at least partially removed. Such removal can be by grinding chamfers or removing the outer cutting edge entirely in the initial gullet grinding step. <IMAGE>

Description

CUTTERS This invention relates to cutters. More specifically, the invention relates to annular cutters having spaced teeth at one end, these teeth defining radially inner and outer cutting edges at differing radial distances from the longitudinal axis of the cutter.

In previously proposed cutters of this kind, such as those disclosed in GB1,403,041 and 1,403,042 each tooth defines both an inner and an outer cutting edge and the preferred arrangement is that these cutting edges produce individual chips of removed metal or swarf.

While the cutters disclosed in these prior patents possess certain advantages over their predecessors, we have established that they nevertheless are subject to certain significant shortcomings including, in certain circumstances, performance shortcomings, a tendency to produce excessive noise, and (which is not unconnected with their performance) a need for improved swarf or chip clearance.

Prior proposals have been made for annular cutters to meet the above shortcomings. These proposals include ones in which the tooth geometry of successive teeth is modified by means of abrasion techniques to reduce noise generation, for example. However, while in this latter respect some success has been achieved, the performance has been hampered by a related shortcoming in terms of the rake angle of the relevant teeth.

An object of the present invention is to provide annular cutters offering improvements in relation to one or more of the matters discussed above, or generally.

According to the invention there is provided an annular cutter as defined in the accompanying claims.

In a preferred embodiment, an annular cutter comprises a generally cylindrical hollow main tool body which has drive connection means at one end. Cutting means is provided at the other end, the cutting means comprising a plurality of teeth at spaced intervals around the annular periphery of the tool body. A plurality of cutting edges are defined by the teeth, these edges including inner and outer cutting edges at differing radial distances from the longitudinal rotational axis of the cutter. Each tooth is of generally similar form to the next tooth. Each tooth also has only an inner cutting edge or an outer cutting edge. For each tooth having an outer cutting edge, the portion thereof corresponding to an inner cutting edge is at least partially removed.Likewise, for each tooth having an inner cutting edge the portion thereof corresponding to an outer cutting edge is at least partially removed.

The inner and outer cutting edges are arranged alternately around the periphery of the cutter. The portion removed from each tooth is removed by grinding a chamfer thereon, the chamfer being inwardly inclined for an inner cutting edge removed, and outwardly inclined for an outer cutting edge removed.

Alternatively, the portion removed from each tooth may be removed by grinding away the portion corresponding to an outer cutting edge entirely, at least in the region of the cutting edge removed. This may be done by grinding a double width gullet in the external surface of the tool body. In that case, an inwardly inclined chamfer may be employed for removing, partially, the relevant inner cutting edges.

In another preferred embodiment, each tooth has an edge corresponding both to an inner cutting edge and an outer cutting edge, but only one of these edges is so positioned to be able to cut in normal use. At least the outer cutting edges have a positive rake angle ie are inclined forwardly and radially outwardly with respect to the direction of rotation of the cutter.

The portions removed from the cutter are removed by grinding a chamfer accross the entire tooth, the chamfer being inclined in one direction only, for that particular tooth. The chamfers on successive teeth are inclined alternately one way and the other, ie inwardly and outwardly, with respect to the axis of the cutter. Said inclination of the chamfer with respect to a radius through the axis preferably lies in the range of 3 degrees to 9 degrees, the preferred inclination being about 6 degrees.

The positive rake angle of the outer cutting edges preferably lies in the range of 2 degrees to 15 degrees with respect to a radius through the cutting edge.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which Fig 1 shows an end view of an annular cutter at a preliminary stage in its manufacture; Fig 2 shows a side elevation view of the cutter of Fig 1; Fig 3 shows a partially cut-away view of the cutter of Figs 1 and 2, the cut-away or section being taken on the line 111-111 in Fig 2; Fig 4 shows a view, corresponding to that of Fig 1, illustrating a further stage in the manufacturing process; Fig 5 shows a side elevation view of the Fig 4 stage; Figs 6, 7 and 8 illustrate views of a third stage in the manufacturing process, Figs 6 and 8 corresponding to Figs 4 and 5, and Fig 7 being a scrap section on the line VII-VII in Fig 6; Figs 9, 10, 11 show a fourth stage, corresponding to that of Fig 6 to 8; and Figs 12 to 15 illustrate stages in a final grinding operation wherein certain portions of the teeth are removed.

As shown in the drawings an annular cutter 10 comprises a generally cylindrical hollow main tool body 12 having drive connection means (now shown) such as a cylindrical spigot to be received in the chuck of a drill, at one end of the cutter, and cutting means 14 at the other end.

Cutting means 14 comprises a plurality of teeth 16 at spaced intervals around the annular periphery of the tool body 12.

A plurality of cutting edges (to be more fully described below) are defined by the teeth 16. These cutting edges are produced in subsequent stages of the manufacturing process and include inner and outer cutting edges at differing radial distances from the longitudinal axis 18 of cutter 10. In Fig 1, the general locations of the inner and outer cutting edges are indentified by reference numerals 20 and 22 respectively, even though these edges have not yet been formed as cutting edges.

In the embodiment the tool body 12 has been formed with six flutes or gullets 24 extending helically around the outer periphery of the tool body and serving to define the outer cutting edges 22. The inner cutting edges 20 are formed, as shown, by grinding, initially, three generally radial gullets or flutes 26. As clearly shown in Fig 2, the gullets 26 are outwardly and outwardly inclined, opening into the gullets 24, which latter serve to carry away metal swarf axially of the cutter.

In this embodiment, the general structure and arrangement and mode of manufacture of the cutter 10 is generally similar to those described in the above-mentioned prior GB patents, to which reference is hereby directed, subject of course to the differences (to be described more fully below) relating to the provision of only one cutting edge per tooth and the removal or partial removal of the structure relating to the other cutting edge.

In the next stage of the manufacturing process, illustrated in Figs 4 and 5, three further flutes or gullets 28 are ground in the end wall of tool body 12, thereby defining six discrete teeth 16.

The angular inclination of gullets 28 differs from that of gullets 26, the former being approximately radial while the latter are inclined to radii so that the inner cutting edges 20 are inclined so that their leading edge with respect to the direction R of rotation is the leading edge.

In the finished cutter 10, the gullets 28 serve to define edges, otherwise corresponding to the inner cutting edges 20, but which do not effect a cutting action.

In the stage illustrated in Fig 6, 7 and 8, the inner cutting edges 20 are ground so as to produce the necessary cutting profile with a leading edge extending forwardly in the direction R, for cutting purposes.

Fig 7 shows the slightly outwardly chamfered profile of the upper surfaces of the forward edges of the teeth 16 at this stage In the manufacturing stage illustrated in Figs 9, 10 and 11, the outer cutting edges 22 are provided with the appropriate profiles for cutting purposes. Figs 10 and 11 show the inwardly-inclined chamfers provided in the relevant teeth 16 having the edges 22 at this stage in the manufacturing process.

Finally, in Figs 12 to 15 there is illustrated the stages in which the structures on each tooth 16 which provide the means for producing a second cutting edge thereon are removed by grinding. As shown in Figs 12 and 13, the outer portion 30 of each tooth 16 having an inner cutting edge 20 is partially removed by forming an outwardly inclined chamfer thereon, at 45 degrees with respect to the axis 18 of the cutter.

Likewise, as shown in Figs 14 and 15, for each tooth 16 having an outer cutting edge 22, the inner portion 32 is partially removed by grinding an inwardly-directed chamfer at 35 degress with respect to axis 18.

In operation of the cutter 10, the provision of alternate inner and outer cutting edges one on each tooth 16 is found to provide an unexpectedly effective cutting action. This is promoted by the efficient swarf removal permitted by the extra space therefor due to the partially removed structure of the non-operational portions of the teeth.

In a further embodiment, not illustrated, the outer portions of the teeth having inner cutting edges are removed entirely by grinding double width main gullets or flutes 24. In this embodiment, for those teeth having an outer cutting edge, the inner portion removed on the relevant teeth is removed by grinding an inwardly directed chamfer.

Interestingly, in the above embodiments, there has been provided an annular cutter offering significantly improved cutting performance due to separation of the cutting actions and increased space for swarf clearance, the generation of swarf at relatively widely spaced intervals serving to enhance this improved cutting action.

In a still further embodiment, not illustrated, the cutter is produced exactly as described above with reference to Figs 1 to 11 of the drawings, but the steps described above with reference to Figs 12 to 15 are omitted, that is to say the stages in which the internal and external chamfers are ground on successive teeth to remove the respective internal and external cutting edges.

Thus, in this embodiment, the cutter as produced in the stage described with reference to Figs 9, 10 and 11 represents the finished cutter. As in the illustrated embodiment, only one edge actually cuts in use on each tooth, in normal use. Thus, referring to Fig 9, the outer cutting edges 22 effect cutting on the three teeth identified in Fig 9 by the reference letter A. In those teeth A, the inner edge 50 is not a cutting edge on account of the chamfer indicated in Fig 10 by the arrows 52, namely a chamfer of 6 degrees.

It will be noted from Fig 10 that the chamfer 52 is inclined inwardly with respect to a radius 54 from the axis 56 of the cutter.

Likewise, referring to Figs 6, 7 and 8, the inner cutting edges 20 effect cutting on the three teeth identified in Fig 6 by the reference letter B. In those teeth B, the outer edge 58 is not a cutting edge on account of the chamfer indicated in Fig 7 by the arrows 60, namely a chamfer of 6 degrees.

It will be noted from Fig 7 that the chamfer 60 is inclined outwardly with respect to a radius 62 from the axis 56 of the cutter.

Thus, each tooth 16 of the cutter 10 has only an inner cutting edge or an outer cutting edge, the edge which would otherwise cut having been at least partially removed by the chamfering operation.

In addition, the outer cutting edges 58 have, as shown in Fig 6, a positive rake angle with respect to a radius 64 througn the axis 56 of the cutter. In Fig 6, the positive inclination is barely visible in relation to the cutting edge 58 of the tooth B at top dead centre position. The positive inclination is such that the radially outermost end of the cutting edge is slightly forward (in the direction of rotation R) of the innermost end of the cutting edge. This promotes a highly positive cutting action leading to a notably more efficient cutting effect in use than prior proposals utilising a negative rake angle.

In this embodiment, the grinding steps described in relation to Figs 6 to 11 of the drawings are carried out by milling techniques which avoid the progressive tendency to a negative rake angle inherent in previously proposed techniques for producing annular cutters of this general kind.

Interestingly therefor, the above embodiment provides a simplified cutter construction (as compared with the first embodiment), whereby production costs are reduced and the cutting efficiency shortcomings of prior proposals are overcome.

Claims (13)

1 An annular cutter comprising a) a generally cylindrical hollow main tool body; b) drive connection means at one end of said tool body; c) cutting means at the other end of said tool body; d) said cutting means comprising a plurality of teeth at spaced intervals around the annular periphery of said tool body at said other end; e) a plurality of cutting edges defined by said teeth, said cutting edges including inner and outer cutting edges at differing radial distances from the longitudinal axis of said tool body; f) said teeth being of similar general form to each other; characterised in that g) each tooth has only an inner cutting edge or an outer cutting edge; h) for each tooth having an outer cutting edge the portion thereof corresponding to an inner cutting edge being at least partially removed; and i) for each tooth having an inner cutting edge the portion thereof correpsonding to an outer cutting edge being at least partially removed.

2 An annular cutter having teeth defining inner and outer cutting edges, each tooth having only an inner or an outer cutting edge, the portion thereof corresponding to the non-present cutting edge being at least partially removed.

3 A cutter according to claim 1 or claim 2 characterised in that said inner and outer cutting edges are arranged alternately around the periphery of said cutting means.

4 A cutter according to any one of the preceding claims characterised in that said portion removed is removed by grinding a chamfer thereon, said chamfer being inwardly inclined for an inner cutting edge removed, and outwardly inclined for an outer cutting edge removed.

5 A cutter according to any one of claims 1 to 3 characterised in that said portion removed is removed by grinding away the portion corresponding to said outer cutting entirely, at least in the region of said cutting edge removed.

6 A cutter according to claim 5 characterised in that said outer cutting edges are removed by grinding a double width gullet in the external surface of said tool body.

7 A cutter according to claim 6 characterised in that said inner cutting edge is removed by grinding an inwardly inclined chamfer on the relevant teeth.

8 A cutter according to any one of claims 1 to 3 characterised in that each tooth has edges corresponding both to an inner cutting edge and an outer cutting edge, but only one of said edges is so-positioned so as to be able to cut in normal use, and at least said outer cutting edge has a positive rake angle.

9 A cutter according to claim 8 characterised in that said portions removed are removed by grinding a chamfer across the entire tooth, said chamfer being inclined in one direction only (ie inwardly or outwardly) for that particular tooth.

10 A cutter according to claim 9 characterised in that said chamfers on successive teeth are inclined alternately one way and the other (ie inwardly and outwardly) with respect to the axis of the cutter.

11 A cutter according to claim 10 characterised in that the inclination of said chamfers with respect to a radius through the axis lies in the range of 3 degrees to 9 degrees.

12 A cutter according to any one of claims 8 to 11 characterised in that said positive rake angle lies in the range of 2 degrees to 15 degrees.

13 An annular cutter substantially as described herein with reference to the accompany drawings.