GB2293121A

GB2293121A - Boring tool and tool holder

Info

Publication number: GB2293121A
Application number: GB9515830A
Authority: GB
Inventors: Kenneth Atkins
Original assignee: C L A TOOLS Ltd
Current assignee: C L A TOOLS Ltd
Priority date: 1994-09-14
Filing date: 1995-08-02
Publication date: 1996-03-20
Also published as: GB9418505D0; GB9515830D0

Abstract

A tool 10 and a tool holder assembly for boring or back boring comprises an insert 14 adapted to be secured in a tool holder 11 having at least one chip removal flute 13, the tool being clamped in a seating at a leading end and leading edge of the flute 13 by a clamp 15, wholly recessed so as not to interrupt the flute. The clamp 15 and insert 14 have an interengaging tapered constant cross-section projection 21 and recess 19 of trapezium shape, providing exact location and self-centring. The insert 14 is radially adjustable by an adjuster screw 26 bearing on the inner end or by an adjuster peg with a flat or conical point on which an adjuster screw is arranged to bear. <IMAGE>

Description

BORING TOOL AND TOOL HOLDER This invention relates to a tool and a tool holder assembly for boring or back boring.

Boring tools are used to enlarge drilled or otherwise formed holes or bores to precise tolerances. Back boring tools are used to enlarge portions of bores by working towards the accessible face of the work piece, in contrast to the usual method of boring working from the accessible face into the bore.

In each case, metal must be removed by a cutting tool acting on the surface of the bore while the tool or work piece rotates about the axis of the bore.

It is essential for the tool to be held firmly and immovably in the tool holder during the boring operation. Furthermore, the tool must be clamped in a precise position so as to give the exact bore dimensions required and so as to remove the precisely required quantities of metal. It is desirable for the tool to be capable of easy adjustment, removal and replacement. Finally, the metal swarf or chips formed as the tool cuts need to be removed efficiently so that they do not mark the bore which is being machined.

It is an object of the present invention to provide a tool and to provide a tool holder assembly which assists in achieving some or all of these desirable objectives.

According to the invention there is provided a boring tool comprising an insert adapted to be secured in a tool holder to form a tool holder assembly, the boring tool having a cutting edge, an inclined back surface trailing behind the cutting edge in use, and an elongate recess in a surface opposed to said back surface, the recess being of constant trapezium shape in cross-section and having a base and a pair of boundary walls inclined at equal angles and tapering towards each other considered in a direction towards the base.

Viewed from a further aspect, the invention provides a tool holder including a body having at least one relieved chip removal flute (as defined), a tool seating including an inclined back seating surface trailing behind the leading end of the flute and adapted to cooperate with a back surface of the tool insert, the tool seating being provided at a leading end and leading edge of said flute, a clamp adapted to at least partly overlie the tool seating to clamp the tool insert against the tool seating, the clamp being wholly recessed in the body so as not to obstruct the flute and having an elongate projection of constant trapezium shape in cross-section and having a base and a pair of boundary walls inclined at equal angles and tapering towards each other considered in a direction towards the base, the projection being adapted to overlie the tool insert in use and to cooperate with the elongate recess of the tool insert to locate and centre the tool insert relative to the tool seating.

The tool holder may have two symmetrically disposed flutes and be adapted to hold two tools. Alternatively it may have a number of flutes greater than two and being adapted to hold a corresponding number of tools.

The tool holder may have elongate recesses in its periphery parallel to the axis and adapted to receive wear pads.

Viewed from a still further aspect the invention provides a tool holder assembly for boring or back boring comprising, in combination, a tool holder and a tool insert as previously set out.

In the tool holder assembly, the tool holder may have a hole adapted to receive an adjuster screw bearing on a radially inner end portion of the tool insert positioned in the seating to cause relative movement along the axis of elongation of the cooperating recess and projection in the tool insert and clamp respectively when the clamp is not fully tightened.

In the tool holder assembly, the tool holder may have a hole adapted to receive an adjuster screw, an adjusting peg being provided having a flat or conical point bearing on the insert, and the adjuster screw being arranged to contact and move the adjusting peg.

The invention will now be described in more detail by way of example only with reference to the accompanying drawings in which, Figure 1 is a side elevational view of a boring tool holder assembly, Figure 2 is a side elevational view of the tool holder assembly taken at 90" to the view in Figure 1, Figure 3 is an end elevational view of the tool holder assembly of Figures 1 and 2, Figure 4 is an end elevational view of a modified tool holder assembly having two boring tools, Figure 5 is an enlarged diagrammatic view of a tool insert showing its clamping means Figure 6 is a front elevational view of the clamping means of the tool insert.

Figure 7 is a side elevational view of the tool insert showing its clamping means.

Figure 8 is a side elevational view of a modified boring tool holder assembly, Figure 9 is an end elevational view of the tool holder assembly of Figure 8 Figure 10 is an enlarged front vieu of a modified tool insert, Figure 11 is a side elevational view of the modified tool insert of Figure 10.

Referring to the drawings, a boring tool is generally indicated at 10 and includes a generally cylindrical body 11 adapted to be secured by conventional means 12 in a boring machine. The body 11 has a chip removal flute 13. Although this is referred to as a "flute" it need not necessarily take the form shown and in particular the tool body 11 be eccentric for use in back boring and hence the flute may take a different form. t!L expression "flute" should be taken to cover any form of relief provided in the body and capable of removing swarf or chippings from the region of the tool insert.

The boring tool 10 further comprises a tool insert generally indicated at 14 which is illustrated in more detail in the enlarged views in Figure 5 to 7, 10 and 11. The tool insert 14 is held in position in the tool holder by a clamp 15 held by a clamping screw 16.

It will be seen in Figure 2 of the drawings that the clamp and clamping screw 15,16 are recessed into the body 11 of the tool holder so as not to obstruct the flute 13. This enables ready clearance of chips and swarf from the cutting region. The insert 14 may have a chip-breaker groove 8 extending throughout its length as shown in Figures 10 and 11, particularly where substantial depth of cut is required, for example in boring and spotfacing. In Figures 5 and 6 the tool insert has a cutting rake 17 in a radial direction for light depths of cut, as in reaming and fine boring.

In Figure 3, it will be seen that a single flute 13 is provided in the tool holder body 11 and a single tool insert 14 is also provided. having a cutting edge 17 projecting slightly from the rotational envelope of the tool holder 11. Thus, the tool holder 11 is a free fit in the hole to be bored and the cutting edge of the tool insert projects at 17 to remove a finely controlled portion of metal from the bore when the body 11 of the tool holder and the bore has been formed are in relative rotation. It will be appreciated that either the tool or the workpiece in which the bore is made may be rotated, to the same effect.

Figure 4 shows an alternative form of boring tool in which two flutes 13 are provided and two boring tool inserts 14 are also provided, each having a cutting edge 17.

A single boring tool insert may be preferred in situations where very fine tolerances are required. As shown in Figures 8 and 9, the body 11 of the boring tool holder 10 is then provided with support pads 9 provided in elongate recesses running parallel to the axis of the tool holder 10 and acting to centre the tool holder in the bore. Such pads 9. of tungsten carbide or titanium carbide, assist in centring the boring tool and reducing vibration.

Where very fine tolerances are less important, a higher feed rate can be achieved using two inserts 14 as shown in Figure 4, or even more. A larger number of flutes, particularly an odd number, reduces the possibility' of vibration and chatter.

Turning to the details of clamping the inserts 14, reference is made to Figures 5 to 7. The insert 14 has a shaped cutting edge 17 which is machined and projects slightly as illustrated in the preceding figures from the tool. The insert 14 has an inclined back surface 1 8 which trails behind the leading edge and leading end of the flute 13 in use as seen in Figure 2.

The inclined back surface mates with corresponding surface recesses within the tool holder body 11 and the effect of having the trailing surfaces in contact is that some of the cutting force is resolved into a component acting along the back surface 18, tending to hold the tool insert 14 more closely into its seating.

On the face of the insert 14 which is opposite to its back surface 18, a recess 19 is provided. This is an elongate recess extending right across the tool insert as best seen in Figures 6. 10 and 11. The recess 19 is of constant tapering cross-section, more specifically of trapezium shape. It has a flat base 20 which is parallel to and diametrically opposed to the back surface 18. The trapezium shape cross-section also has a pair of boundary walls 7 inclined at equal angles and tapering towards each other considered in a direction towards the base.

The clamp 15 has a mating projection 21 which overlies the recess 19 and has a similar tapering trapezium shape in cross section. with a base and a pair of boundary walls inclined at equal angles and tapering towards each other in a direction towards the base.

However. the base of the projection may not necessarily meet the base 20 of the recess of the tool insert. Thus. as the clamp 15 is lowered down onto the insert 14, the projection 21 mates with the recess 19 and tends to centre the insert 14 in a correct, and repeatable position. The projection overlies the tool insert in use and cooperates with the elongate recess of the tool insert to locate and centre the tool insert relative to the tool seating.

The clamp 15 is operated by means of a screw arrangement 16 in which a two-part screw thread 22 is used to give up and down movement of the clamp 15 relative to a threaded hole in the body 11 of the tool holder.

The clamp has a top surface 23 which lies flush with or recessed behind the leading edge 24 of the flute 13 so that the flute is entirely devoid of obstructions.

In order to position the tool insert 14 in the tool holder 10, the insert is hooked under the projection 21 of the clamp which is tightened down until the tool insert is loosely held.

It will be appreciated that the mating trapezium shaped recess and projection 19,21 provide a slideway for the tool insert to be moved laterally so that the cutting edge 17 projects more or less from the envelope of the boring tool as indicated in chain dotted lines 25 in Figure 5.

Control of the inward and outward movement of the tool insert 14 is achieved by an adjusting screw 26, which is a grub screw acting in a hole provided obliquely behind the tool insert 14. The grub screw 26 is obliquely angled and bears on the back edge or surface of the insert 14, allowing it to be gradually moved in or out to achieve precise setting of the position of the cutting edge 17. Once this precise positioning has been achieved, the clamping screw 16 is tightened so that the insert is firmly held, centred and located by the interaction of the trapezium shaped projection and recess 21 and 19.

As an altemative, the grub screw 26 may push against the end of an adjusting peg, which may have a single flat or conical point at the other end which aligns with the rear face of the insert.

Rotation of the clamp 15 relative to the screw 16 is prevented because the clamp has side faces 27 which seat in corresponding cut-outs in the tool holder and prevent rotation around the axis of the clamping screw 16. This in turn prevents any wobbling of the tool insert 14. Thus the tool insert 14 is precisely positioned in a repeatable manner by the setting of the adjusting grub screw 26, the cooperation of the back surface 18 with the corresponding surface of the tool holder and the precise positional interlock with the clamp 15, due to the engagement of the side walls 27 in their housing in the tool holder body 11 and the self-centring action of the projection 21 in the recess 19 of the tool insert 14.

It will therefore be seen that the tool insert 14 is held firmly and immovably in the tool holder during the boring operation once the clamping screw 16 has been fully tightened.

Repeatability, easy removal and replacement are also provided. Additionally since the flute or flutes 13 is or are not obstructed, efficient chip or swarf removal is ensured.

Claims

1. A boring tool comprising an insert adapted to be secured in a tool holder to form a tool holder assembly, the boring tool having a cutting edge, an inclined back surface trailing behind the cutting edge in use, and an elongate recess in a surface opposed to said back surface, the recess being of constant trapezium shape in cross-section and having a base and a pair of boundary walls inclined at equal angles and tapering towards each other considered in a direction towards the base.

2. A tool holder including a body having at least one relieved chip removal flute (as defined), a tool seating including an inclined back seating surface trailing behind the leading end of the flute and adapted to cooperate with a back surface of the tool insert, the tool seating being provided at a leading end and leading edge of said flute, a clamp adapted to at least partly overlie the tool seating to clamp the tool insert against the tool seating, the clamp being wholly recessed in the body so as not to obstruct the flute and having an elongate projection of constant trapezium shape in cross-section and having a base and a pair of boundary walls inclined at equal angles and tapering towards each other considered in a direction towards the base, the projection being adapted to overlie the tool insert in use and to cooperate with the elongate recess of the tool insert to locate and centre the tool insert relative to the tool seating.

3. A tool holder according to Claim 2 and having two symmetrically disposed flutes and being adapted to hold two tools.

4. A tool holder according to Claim 2 and having a number of flutes greater than two and being adapted to hold a corresponding number of tools.

5. A tool holder according to any one of Claims 2 to 4 and having elongate recesses in its periphery parallel to the axis and adapted to receive wear pads.

6. A tool holder assembly for boring or back boring comprising, in combination. a tool holder according to any one of Claims 2 to 5 and a tool insert according to Claim I

7. A tool holder assembly according to Claim 6 wherein the tool holder has a hole adapted to receive an adjuster screw bearing on a radially inner end portion of the tool insert positioned in the seating to cause relative movement along the axis of elongation of the cooperating recess and projection in the tool insert and clamp respectively when the clamp is not fully tightened.

8. A tool holder assembly according to Claim 6 wherein the tool holder has a hole adapted to receive an adjuster screw, an adjusting peg being provided having a flat or conical point bearing on the insert, and the adjuster screw being arranged to contact and move the adjusting peg.

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

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

11. A tool holder assembly substantially as hereinbefore described with reference to.

and as illustrated in, the accompanying drawings.