GB2057940A

GB2057940A - Cutting tool, e.g. a slot cutter or a broach

Info

Publication number: GB2057940A
Application number: GB8028157A
Authority: GB
Original assignee: HERTAL G
Current assignee: HERTAL G
Priority date: 1979-09-01
Filing date: 1980-09-01
Publication date: 1981-04-08
Also published as: IT8024364A0; GB2057940B; FR2464115A1; DE2935426A1; JPS5639810A; IT1132584B

Abstract

A milling cutter or broach has its cutting edges formed on replaceable inserts (2) held in place by respective bent shank clamping bolts (4) in raked bores (9) each pulled down the bores by a respective grub screw in a tapped bore (23) engaging a notch in the bolt shank. The rake of the bore (9) pulls each insert (2) back against a transversely raked cutting pressure bearing surface to urge the insert (2) cammingly sideways against a guide surface extending along the feed direction of the tool holder (1). <IMAGE>

Description

SPECIFICATION Cutting tool, e.g. a slot cutter or a broach The invention relates to a cutting tool, such as a slot cutter or a broach.

Known cutting tools such a milling cutters or broaches may be driven longitudinally or rotationally. Such cutting tools may have a multiplicity of cutter inserts which have to be replaced by new cutter inserts once their tool life has been reached. There is a problem in ensuring uniformity in positioning of the respective exchanged cutter inserts by use of only simple means. With one known cutting tool of this type, as disclosed in DE-PS 22 31 550, this positioning is achieved in that the main cutting pressure bearing surface of the holder recess has a V-shaped design with the two legs of the V symmetrical about the central plane of the tool. The resultant effect is a self-centering of the cutter insert under the clamping pressure exerted by the insert clamping bolt and the main cutting pressure exerted in operation.However, such a Vshaped design of the main cutting pressure bearing surface can only be obtained with relatively wide cutting tools, that is to say milling cutters with relatively long cutting edges. Moreover, the V-shaped design of the main cutting pressure bearing surface is relatively costly to produce.

Accordingly, the problem confronting this invention is the production of a tool such that even with very narrow tool designs, that is to say with relatively short cutting edges of the milling cutter inserts, a trouble-free centring or positioning of the cutter inserts after an exchange is ensured.

Accordingly the present invention provides a machine tool which may be longitudinally or rotationally driven, comprising: at the periphery or on the longitudinal side of a holder, a plurality of interchangeably fixed cutter inserts with a saw tooth type action; wherein each said cutter insert is secured in a respective holder recess and held against at least a main cutting pressure bearing surface of the holder recess by means of a clamping bolt received in a cut out of the cutter insert; wherein the cutting edge of each cutter insert extends across the whole width of the holder and is effective on both sides of the said holder; wherein the cutter insert engages a guide arranged on the reaction bearing surface of the said holder recess which extends in the feed direction of the tool; and wherein said main cutting pressure bearing surface of the holder recess is flat and extends at an acute angled transverse rake with respect to the feed direction such that by means of the clamping bolt pressure and of the main cutting pressure the cutter insert is unilaterally pressed across the main cutting bearing surface and retained against a lateral surface of said guide.

By giving the main cutting pressure bearing surface a rake, there is produced during the tightening of the clamping bolt and under the efect of the main cutting pressure operating on the cutter insert in use, a pressure component acting on the cutter insert at right angles to the tool feed direction which firmly pushes the latter unilaterally against a guide surface on the holder. Since this guide surface extends in the longitudinal tool feed direction, in particular in the direction of the longitudinal central plane of the tool, the method of production of the tool is straightforward.

Preferably, the cutter insert surface opposite the flank is provided with a groove extending along the feed direction of the tool, and said guide on the reaction surface of the holder recess comprises a longitudinal strip to engage within the groove with a spring type action. During the sintering of the cutter insert, the exact position can be provided for the groove therein. The same applied to the longitudinal strip on the reaction surface.

Advantageously, the holder recess includes a bore passing through said guide to receive the clamping bolt in such a way that the guidance of the strip is effective to both sides of bore. This characteristic ensures the effectiveness of the longitudinal strip over a long dimension, it being possible to absorb particularly well with a long lever arm any possible lateral deflecting forces acting on the cutter insert.

Suitably, said longitudinal strip ends at a distance ahead of said main cutting pressure bearing surface. This makes it possible to manufacture the main cutting pressure bearing surface straightforwardly in a continuous milling process. The invention is particularly suitable for those cutter inserts whose longest dimension is opposed to the main cutting pressure, that is to say, those which are arranged for instance, on a slot cutter in a tangential direction on the periphery of a rotary holder.

In order that the present invention may more readily be understood the following description is given, merely by way of example, of an embodiment of the invention represented in the accompanying drawings, in which:~ Figure 1 is a side view of a detail of the periphery of a slot cutter designed in accordance with the invention; Figure 2 is an exploded view of a saw tooth cutter insert and clamping device; Figure 3 is a section taken on the line Ill-Ill of Fig. 2, with the clamping device in a tightened position; Figure 4 is a side view of the holder recess along the direction of arrow IV in Fig. 2; Figure 5 is a plan view of the holder recess along the arrow V in Fig. 4; and Figure 6 is a plan view of a cutter insert for use in a tool in accordance with the invention.

On the periphery of the milling cutter holder or body 1, having a design similar to that of a circular saw disc, there is interchangeably fixed a multiplicity of cutter inserts 2 with a saw tooth action, in particular laminar inserts made of a hardened cutting material e.g.

carbide metal. Cutter insert 2 is fixed in a respective cutter recess 3 which is delimited on two sides, by use of a clamping bolt 5 passing through a cut-out 4 in the cutter insert. In its tightened position the clamping bolt 5 has its part-spherical head 6 in a corresponding part-spherical counter-sunk bore 7 of the cutter insert cut-out 4. The shank 8 of the bolt 5 projects through the cutout 4 and into a raked bore 9 which is drilled into holder 1 to extend at an acute angle 10 (Fig. 1) of preferably approximately 45 to the radial direction of the tool in its longitudinal centre plane.

As shown more clearly in Fig. 6, the spherically counter-sunk bore 7 in the tool insert has a pair of parallel flats which correspond to similar flats formed on the head of the clamping bolt 5.

The cutting edge 12 of the cutter insert extends over the whole width of the holder 1.

On both sides of the holder 1 its cutter corner tips 14 project beyond the plane of the flat side 13 of the holder 1.

The cutter insert surface 16 which is opposite to the flank 15 of the cutter insert 2 is provided with groove 17 extending along the tool feed direction 11. The reaction surface 18 of the holder recess 3 has a longitudinal strip 19 which engages in the groove 17 with a spring type action. The main cutting pressure bearing surface 20 of the holder recess 3 is flat, and extends at an acute angle 21 (Fig.

5), that is to say with a transverse rake to the peripheral or the feed direction 11 of the tool.

Bore 9 for the passage of clamping bolt 5 passes through this longitudinal strip 19 in such a way that the guidance of cutter insert 2 by the longitudinal strip 19 is effective to both sides of, i.e. in front of and behind, the bore 9. The longitudinal strip 19 ends at a distance 22 ahead of the main cutting pressure bearing surface 20 to avoid any interference between the front end of the longitudinal strip 19 and the lateral movement of the cutting tool insert 2 as the insert moves during tightening of the clamping bolt 5 by means of grub screw 24 (to be described below). The spacing 22 also facilitates production of the tool, as indicated above. The rear edge 32 of the flank 15 of cutter insert 2 is raked with rake 23 which matches that of the main cutting pressure bearing surface 20 of the holder recess 3.

Tightening of clamping bolt 5 is effected in a known way by means of a grub screw 24 inserted radially inwardly into a tapped hole 23 of the holder 1 so that the front tip 25 of the grub screw 24 engages that flank 26 of a clamping bolt notch 27 arranged in the bent shank of bolt 5 which faces away from the bolt head 6. By screwing up the grub screw 24, the clamping bolt 5 is drawn into the holder along the direction of the longitudinal axis 28 of raked bore 9 thereby to secure the cutter insert 2 in place within the cutter recess 3. At the same time, the transverse rake of the main cutting pressure bearing surface 20 produces on the cutter insert 2 a lateral pressure component 29 which firmly presses side edge 30 of the groove 17 against the side 31 of longitudinal strip 19 and thereby produces the exact positioning of the cutter insert 2 within the holder recess 3.

Although the present invention has been exemplified in terms of a milling cutter where the holder 1 is rotated to perform the cutting action, the invention can equally well be embodied in a broach where the holder is elongate and the feed direction extends along the longitudinal axis of the holder.

Claims

1. A machine tool which may be longitudinally or rotationally driven, comprising: at the periphery or on the longitudinal side of a holder, a plurality of interchangeably fixed cutter inserts with a saw tooth type action; wherein each said cutter insert is secured in a respective holder recess and held against at least a main cutting pressure bearing surface of the holder recess by means of a clamping bolt received in a cut out of the cutter insert; wherein the cutting edge of each cutter insert extends across the whole width of the holder and is effective on both sides of the said holder; wherein the cutter insert engages a guide arranged on the reaction bearing surface of the said holder recess which extends in the feed direction of the tool; and wherein said main cutting pressure bearing surface of the holder recess if flat and extends at an acute angled transverse rake with respect to the feed direction such that by means of the clamping bolt pressure and of the main cutting pressure the cutter insert is unilaterally pressed across the main cutting bearing surface and retained against a lateral surface of said guide.

2. A machine tool according to claim 1, wherein said cutting tool inserts are laminar and formed of hardened metal.

3. A machine tool according to claim 1 or 2, wherein the cutter insert surface opposite the flank is provided with a groove extending along the feed direction of the tool, and said guide on the reaction surface of the holder recess comprises a longitudinal strip to en gage within the groove with a spring type action.

4. A machine tool according to claim 3, wherein said longitudinal strip ends at a distance ahead of said main cutting pressure bearing surface.

5. A machine tool according to any one of claims 1 to 4, wherein said holder recess includes a bore passing through said guide to receive the clamping bolt in such a way that the guidance of the strip is effective to both sides of bore.

6. A machine tool according to claim 5, wherein said bore is raked with respect to the feed direction of said holder and said clamping bolt has a bent shank to be received in said raked bore.

7. A machine tool according to claim 6, including, for each respective insert, a tapped bore extending perpendicular to the feed direction and intersecting said raked bore, said tapped bore receiving a grub screw which engages a notch in said bent shank to urge said clamping bolt into said raked bore.

8. A milling cutter according to any one of the preceding claims.

9. A broach according to any one of the preceding claims.

10. A machine tool substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.