GB2032820A

GB2032820A - A rotary cutting tool with inserts

Info

Publication number: GB2032820A
Application number: GB7910574A
Authority: GB
Original assignee: TOOLOY Ltd
Current assignee: TOOLOY Ltd
Priority date: 1978-09-18
Filing date: 1979-03-27
Publication date: 1980-05-14

Abstract

A rotary cutting tool e.g. facing or boring tool has a body around whose cutting end there is removably held a circumferential succession of flat- flanked indexable cutting blades 13. The cutting edges of the blades extend generally radially of the tool body. Each blade is removably held in an associated accommodating recess 17, 18 by a screw 19 which enters the cutting end of the body to run down a screw-threaded bore 16 which extends along the body. As the screw is driven into the body, it bears progressively harder with a side of its head against an adjacent flank of the blade to wedge the opposite flank firmly against the side of its accommodating recess. The screws may run parallel to the blade flank, may bear against a reaction-absorbing surface with a tapered headside surface before bearing against the blade flank, or may be spherically-headed. The body may have a pilot 24 protecting inner blade corners. The boring tool blades are outwardly adjusted by a conical surface of a pin 28. <IMAGE>

Description

SPECIFICATION Rotary cutting tool with indexable blades The invention relates to rotary cutting tools with indexable blades.

Known forms of rotary cutting tool - such as boring bars, milling cutters and facing tools usually comprise an elongate and generally circular cylindrical body at one end of which there is arranged a circumferential succession of cutting blades, the cutting blades being made of material noticeably harder and more resistant to wear than the body itself. For instance, the cutting blades can be made of tungsten carbide whilst the main body of the tool is made of less expensive steel.

Some rotary cutting tools have their blades or cutting tips permanently braced into the tool body.

When the cutting edges of the blades are worn, the tool must be removed as a whole from the machine with which it is being used, and the cutting edges must be reground. Once the cutting edges have been reground a certain number of times, there is no longer enough material left on the blades for any further regrinding, and the whole tool must be replaced.

In an effort to overcome this drawback of permanently-brazed blades, cutting tools having removable or so-called "throw-away" blades or tips were developed. The cutting blades of such tools, when worn, can be removed and simply replaced with a fresh and unused set of blades, and the tool can continue to operate with its new set of blades whilst the original blades are being reground. When the cutting blades eventually can be reground no further, only the blades rather than the whole tool need be thrown away.

Tools with throw-away blades are now widely used, and are generally preferred to the older kind of permanently-brazed tool construction.

However, it is self evident that the later throwaway design brings with it a problem of its own, in so far as each blade must be firmly secured to the body of the cutting tool in a manner which will enable it to withstand the very high stresses generated during cutting and to resist successfully the tendency for the blade to be torn away from the cutting tool body.

Several methods have been proposed, and are currently in use, for doing this. They can be classifed generally into those methods based on an overclamp; those using a locking pin; and those using a wedge principle. In general, the clamped and pinned designs make the blades more easily removable, but great care has to be exercised in sufficiently tightening the clamps and pins; whereas on the other hand the wedged designs ensure a tight and stress-resistant fit of the blades, but can be troublesome in setting the blades accurately in the body and in removing them from the body when they need regrinding.

As a further development of the throw-away blade principle, so-called "indexable" blades are now widely used. Such blades have a multiplicity of cutting edges around their periphery, and are so designed that when one cutting edge has been worn the blade need only be turned through 900 in its holding recess in the tool body to bring another cutting edge,into use. Thus, if the blade is basically a four-sided square sliver of tungsten carbide, all four cutting edges could theoretically be used in succession before the blade needed to be removed for regrinding.

Ideally, the optimum blade-fixing design would adapt the highly positive wedge-fixing principle to the later, more convenient and economic indexable type of blade. Unfortunately this is not easy to do, although there are several designs of wedged blade currently on the market which attempt a solution.

In one known design, the two major opposed flat faces - the flanks - of each blade are ridged and the blade is a force-fit in a correspondinglygrooved recess formed in the cutting end of the tool body. The grooves run longitudinally of the tool body, so that the interaction between them and the blade ridges resists the tendency for the blade to be torn radially out of the body during use. A positive wedging blade-clamping action is thus achieved.

With this design, however, the blade flank can be held in only one orientation relative to the tool body; and the blade therefore cannot be "indexed" to use successive cutting edges.

In another known design, each removable blade is clamped into its recess by screws which, like the blades, enter the tool body radially. As each screw is driven home, the side surfaces of its head (or the crests of its fhreads) bear progressively harder against an adjacent flank of the blade to wedge the blade firmly against one side of its recess. U.K. Patent Specifications Nos. 512,274 (Miller) 1,280,718 (Fagersta) and 1,284,435 (Fagersta) all show examples of this second design, which -theoretically-should enable the blades to be indexed as their cutting edges wear.

In practice, however, the tool body has to be of fairly substantial diameter to accommodate the length of the radially-entering blade-clamping screws. In many cases, relatively small tools in very common use - for example of about one inch in diameter - simply do not have enough material for this design to be safely embodied.

In one aspect, therefore, the invention lies in the realisation that a,wedge-clamping screw can successfully be adapted to hold securely a truly indexable blade in even a rejatively small-diameter tool, by driving the screw generally axially, not radially, into the tool body.

A rotary cutting tool (such as a milling cutter, a boring bar or a facing tool) embodying this aspect having a generally circular-cylindrical body around whose cutting end there is removably held a circumferentially successive number of flatflanked multiple-cutting-edge "indexable" blades, with the or each such blade being housed in an accommodating recess in the body of the tool so that one flank (or, more usually, each of the two opposed parallel flanks) of the blade extends .generally radially of the tool body and the blade presents a cutting edge substantially parallel to and slightly proud of the side surface or the cutting end face (or both) of the body, is characterised in that the or each blade is removably wedged into its accommodating recess by a screw which is driven generally axially along the tool body to bring a side surface of its head, or the crests of its threads, or both, into contact with an adjacent flank of the blade and so wedge the opposite flank firmly against a wall of the recess.

Because the clamping screw is driven longitudinally into the tool body, it exerts a highly positive wedging force on the blade but requires very little material to support it radially. A fullyindexable square cutting blade can thus be held securely in a relatively small-diameter tool by only a single clamping screw.

it is already known, in the radial-screw designs referred to above, to make the screw head, rather than the crests of the threads, bear against the blade flank, so preventing undue wear and consequent backlash of the threads. It is also known to form the end region of the tool body surrounding the head in such a manner that the head is supported radially when in wedging engagement with the blade, so relieving the screw threads from absorbing the shear forces generated by the wedging action. In each of the two relevant U.K.Patent Specifications 1,280,718 and 1,284,435, these features are achieved by driving the screw at an acute angle towards the blade flank and by tapering the underside of the screw head: as the screw is driven home, the tapered surface contacts the blade flank just before it (or the cylindrical portion of the screw head) bears against the reaction-absorbing surface of the tool body, We have discovered, however, that if irrespective of whether it enters axially or radially the clamping screw is driven approximately parallel to the blade flank, and/or contacts the reaction-absorbing surface first rather than the flank, significant advantages are obtained.Firstly, although the screw-threaded bore may run approximately parallel to the blade flank, absolute parallelism is not essential; whereas the corresponding acutely-angled bore of the known designs must be very accurately machined.

Secondly, the clamping action is more efficient.

Thirdly, there is not the tendency to unseat the blade which can develop with the known angledscrew design if the screw-threaded bore is inaccurately machined. Fourthly, as the clamping screw is released, the flank-contacting portion of the head - which unscrews along, not away from, the flank-tends immediately and conveniently to eject the blade radially from the tool body. Finally, an end face of the screw head extending at right angles to the blade flank acts as an effective swarf-clearing "throat" during use of the tool.

This therefore constitutes a further aspect of the overall inventive concept.

Conventional blades take the form of a small square sliver of cutting metal having four cutting edges bounding two basically parallel flat flanks.

When the blades are wedged into their respective accommodating recesses, the flanks are held parallel with the longitudinal axis of the tool body.

It is, however, conceivable that special blades could be designed for use with cutting tools embodying the invention, in which one flank of the blade runs at an angle to the other or in which the entire blade was held non-parallel to the longitudinal axis of the tool body.

Where the invention is embodied in a facing tool, there will normally project from the cutting end of the facing tool a circular cyclindrical "pilot" to guide the cutting blades of the tool squarely onto the end of the bore which is to be faced. It is normally desirable to end up with a squareshouldered spot-faced area. According to a further development of the invention, the pilot preferably overshadows the adjacent radially innermost corner of the or each blade cutting edge. With such an arrangement, the corner will not be brought into use with the rest of the cutting edge, and when the blade is indexed to its next position an unworn corner will be presented and a clean second cut will be made.

With the arrangement just described, a standard four-edged blade gives at least three completely clean square cuts with the facing tool before any regrinding is needed.

In a further aspect of the invention, provision may be made for varying the effective cutting diameter of the tool by moving the or each blade radially inwardly and outwardly. It is conventionally necessary to reset each blade individually in, for example, the known serrated ridged and grooved wedge clamping designs previously outlined.However, a tool embodying the invention can be fitted with a wedge, for example a cone, which is housed centrally and longitudinally atthacutting end of the tool body, and whose longitudinal surface contacts the radially innermost edge of the or each blade, with means for advancing the wedge for instance by a screw - progressively axially up and down the tool body (i.e. towards and away from the cutting end) so as to move the or each blade progressively radially inward and outward when the blade is not clamped in position by its clamping screw.

Such an arrangement allows each blade to be set simultaneously at the same predetermined radial distance. The blades can then be tightened firmly against the walls of their respective accommodating recesses by the clamping screws first mentioned.

Preferably means are provided to secure the wedge positively in its "set" positions, in order to counteract any tendancy for it to vibrate loose during use of the tool.

The wedge may conveniently be advanced against the action of a compression spring trapped against the inner end of the advancing wedge.

This gives a smoothly progressive action to the movement of the wedge.

In such tools as boring bars and spot facing tools, to which the invention is especially applicable, the length of the tool body may be several times its diameter. In general, in a cutting tool embodying the invention, the length of the tool body may be greater than or less than the cutting-end diameter.

The accompanying drawings show, by way of example only, several forms of rotary cutting tool each embodying the invention. These tools will now be described with reference to the drawings, in which: Figure 1 shows in side elevation one spotfacing tool embodying the invention; Figure 2 shows the tool of Figure 1 in end elevation; Figure 3, drawn to an enlarged scale, shows in "exploded" perspective the method of clamping the individual blades of the tool; Figure 4, enlarged again, is a longitudinal crosssection showing the blade-clamping construction; Figure 5 and 6 are views similar to Figure 4 but illustrating alternative blade-clamping constructions; Figure 7 is a longitudinal part-section through the cutting end of a boring bar embodying the invention; Figure 8, similar to Figure 7 shows a modification to the boring bar;; Figure 9, enlarged relative to Figure 7, shows in perspective the adjusting cone of the boring bar; Figure 10, shows in perspective a modified "pilot" for use with spot-facing tools embodying the invention; and Figure 11, also a perspective view, shows modification to the pilot of Figure 10.

Throughout the drawings, corresponding parts have been given identical reference numerals.

The spot-facing tool shown in Figures 1 to 4 has a generally circular-cylindrical body which, away from its cutting end 1 1, reduces in diameter to an elongate standard-tapered portion 12.

Around the cutting end 11 of the tool body, four square indexable cutting blades 13 are equally circumferentially spaced. They project radially from the longitudinal axis of the tool body so as to stand slightly proud of both the side surface 14 and the end face 1 5 of the tool body.

Each of these blades 13 is removably wedged into a respective one of four accommodating recesses in the tool body. A respective one of four screw-threaded bores 16 each extending down the tool body opens onto one side 17 of each recess, whilst the other side 1 8 of the recess is flat to receive flat against it one of the two major flat faces of the associated blade 1 3.

One of four allen screws 1 9 makes cooperating screw-threaded engagement with each bore 1 6. The two major flat faces of the blade 1 3 are substantially parallel to one another, and to the longitudinal axis of the tool body. By contrast each bore 16 runs almost - but not quite parallel to the longitudinal axis of the tool body, so that as each screw 19 is driven down its bore 16 it bears progressively harder against the adjacent flat face of the blade. Eventually, the opposite flat face of the blade is wedged firmly against its adjacent side of the recess and the blade is wedged firmly but releasably into the cutting end of the tool body.

In each tool shown, it is the screw head which bears against the blade flat face. Accordingly the cutting end face 1 5 of the tool body is so machined that, when each screw 1 9 is fully driven home, the screw head is radially supported by material around it. It is this material, rather than the screw threads, which resists the force of reaction from the wedging action of the screw head against the blade.

Figure 4 illustrates in enlarged cross-section the way in which each clamping screw 19 holds its associated blade 13 against the side wall 18 of its accommodating recess. The two flanks of the blade are parallel to each other, and the screwthreaded bore 16 which accommodates the screw 19 runs at an accute angle towards the wall 18 of the recess and hence towards the flank of the blade when the blade is in position against the recess. As shown, the underside 21 of the cylindrical screw head 22 is tapered towards the screw threads, and as the screw is driven along its accommodating bore 16 the tapered surface 21 which is parallel with the adjacent blade flank - is brought into frictional wedging engagement with the blade flank.

A curved reaction surface 1 7 is formed diametrically opposite the side wall 18 of the recess. The surface 17 is angled towards the axis of the screw-threaded bore 16, as Figure 4 shows, and the whole arrangement is such that the tapered underside 21 of the screw head contacts the reaction surface 17, is placed under shear stress by the wedging forces generated, and is then thrown radially over against the adajcent blade flank. In other words, the tapered surface 21 of the screw head contacts the adjacent flank of the blade 13 only after it contacts the surface 17.

The surface 17, rather than the screw threads, takes the shear stresses generated by the wedging action.

Figure 5 shows an alternative and presently preferred design, in which the axis of the screw threaded bore 16 is not acutely angled towards the adjacent blade flank but runs parallel with the flank. With this design, it is the cylindrical-surface 22 of the screw head, not the tapered underside 21, which contacts the blade flank. The arrangement is such that as the screw 19 is driven down the bore 16 its tapered underside 21 contacts the reaction surface 17 and is then moved radially over by the consequent wedging interaction so that the cylindrical-surface 22 then bears against the blade flank and wedges the blade firmly into place.

In Figure 5, therefore, the screw head again first contacts the reaction surface 1 7 and is then brought into contact with the adjacent blade flank.

The advantages of such an arrangement have already been outlined.

Figure 6 shows an arrangement similar to that of Figure 5, in which the clamping screw 19 again advances along an axis which is parallel to the adjacent blade flank, and the screw head 23 first contacts the reaction surface 17 and is then brought into wedging engagement with the blade flank. In Figure 6, however, the screw head 23 is a so-called "tulip" head and has a side surface whose envelope is spherical. The wedging contacts between the spherical screw head, the blade flank, and the reaction surface 17 are line contacts, not area contacts.

The tulip headed screw shown in Figure 6 could, like the tapered screw of Figure 5, be used in an arrangement in which the screw axis ran radially, not longitudinally, of the tool body; and was parallel or non-parallel to the blade flank. The tulip-headed screw has a self-seating action which compensates for any inaccuracies in machining the screw bore. A circular-cylindrical steel "pilot" extends in front of the blades 1 8 and axially outwardly from the centre of the end cutting face 15 of the tool body. Its purpose is to guide the blades 13 accurately into the bore (not shown) of the workpiece which is to be spot-faced.The pilot 24 bottoms securely into an accommodating central bore 25 in the tool body, so that it does not prevent the blades 13 from being removed and indexed; but (as Figure 1 shows) it is sufficiently large in diameter to overlap the radially innermost corner of each blade. This prevents the blade corner from being used during a cutting operation, and so, when the blade is indexed, a successive series of at least three unworn corners are presented for the next cut. This helps to ensure squareness of facing.

A relatively small hole 26 is drilled and screwthreaded radially into the tool body and opens onto the bore 25 accommodating the pilot shank.

A grub screw 27 enters the small bore 26 and can be driven home to clamp the pilot 24 securely but releasably in place.

Figure 7 shows a boring bar, as distinct from the spot-facing cutters of Figures 1 to 4. In the boring bar of Figure 7, a centrnlly-axially-located cone 28 can progressively be advanced under the action of an allen screw 29 in order to move all four blades 13 simultaneously radially outwardly by equal amounts. Once the blades have been moved to a desired radial distance, they can then be clamped individually in place using the wedging screws 19 previously described. A grub screw 31 enters a radially-extending bore 32 and clamps the cone-advancing screw 29 finally in place via a brass cusion 38 which prevents damage to the cone screw's threads. This restricts any tendency for the cone screw 29 to vibrate out of place during use of the tool.

A compression spring 34 is helically coiled about the axis of the cone-advancing screw 29.

The screw thus advances the cone 28 against a progressively-increasing biasing force supplied by this spring 34. If the arrangement shown in Figure 7 is abnormally heavily loaded during use, there may be a possible risk of the cone-advacing screw 29 vibrating free from its grub-screw clamp 31 32, 33. If this were to happen, the cone-advancing screw 29 would tend to unscrew itself, the cone 28 itself would begin to move backwards (i.e.

upwards in Figure 7) and the blades 13 would no longer be securely located in place.

Figures 8 and 9 show a modification which attempts to reduce this risk. The blade-contacting faces 35 of the axially-located cone 28 have been machined flat, so that the "cone" is square rather than circular when viewed from its larger end. In addition, a flat 36 has been machined along the lower cylindrical portion of this component, and (as Figure 8 shows) the grub screw 31 now fastens against this flat 36 rather than clamping directly onto the cone-advancing screw 29 as in the arrangement of Figure 7.

With the Figure 8 and 9 arrangement, the cone 28 is secured directly in its finally-adjusted position, rather than being secured indirectly via the cone-advancing screw 29. And the radially inner face of each blade 13 contacts a flat surface, rather than a curved one. Both these measures improve the clamping of the cone 28.

The pilot 24 of the spot-facing tool illustrated in Figures 1 to 4 consists basically of two concentric axially-successive integrally-machined circular steel cylinders of approximately equal length, the smaller-diameter cylinder being gripped as shown by the grub screw 27 which enters the tool radially. In Figure 10, by contrast, the pilot 24 is the same diameter all the way along its length, and a flat 37 - similar to the flat 36 of Figures 8 and 9 - is machined along the left-hand portion of the pilot. When the pilot enters the tool, moving to the left (in Figure 10), the radially-entering grub screw 27 clamps on this flat 37 in a similar manner to the grub screw 31 of Figures 8 and 9.

The other modification to the pilot shown in Figure 10 is to machine four cirumferentiallysuccessive flats 38, defining a square in crosssection, around that portion of the pilot which is contacted by the edges of the four circumferentially-successive blades 13. This gives a positive location to the pilot, whilst still protecting the radially innermost blade corners as previously described.

In Figure 11, another modified form of pilot 24 is shown. Flats 37 and 38, with the same respective functions as the flats of Figure 10, have been machined in this pilot. However, there are now two diametrically-opposed flats 37, each with an associated clamping grub screw 27: and the blade-engaging flats 38 have been recessed into the machined surface to facilitate improved blade location.

The invention could be embodied in a step cutter, as well as the single-diameter cutters described and illustrated.

Claims

1. A rotary cutting tool (such as a milling cutter, a boring bar or a facing tool) having a generally circular-cylindrical body around whose cutting end there is removably held a circumferentially successive number of flat-flanked multiplecutting-edge "indexable" blades, the or each such blade being housed in an accommodating recess in the body of the tool so that one flank (or, where approximate, each of the two opposed parallel flanks) of ttie blade extends generally radially of the tool body and the blade presents a cutting edge substantially parallel to and slightly proud of the side surface or the cutting end face (or both) of the body, characterised in that the or each blade is removably wedged into its accommodating recess by a screw which is driven generally axially along the tool body to bring a side surface of its head, or the crests of its threads, or both, into contact with an adjacent flank of the blade and so wedge the opposite flank firmly against a wall of the recess.

2. A rotary cutting tool (such as a milling cutter, a boring bar or a facing tool) having a generally circular-cylindrical body around whose cutting end there is removably held a circumferentially successive number of flat-flanked multiplecutting-edge "indexable" blades, the or each such blade being housed in an accommodating recess in the body of the tool so that one flank (or, where approximate, each of the two opposed parallel flanks) of the blade extends generally radially of the tool body and the blade presents a cutting edge substantially parallel to and slightly proud of the side surface or the cutting end face (or both) of the body, the or each blade being removably wedged into its accommodating recess by a screw which is driven into the tool body to bring a side surface of its head into contact with an adjacent flank of the blade and so wedge the opposite flank firmly against a wall of the recess, thescrewhead being supported - when in wedging engagement radially of its axis by a reaction surface of the tool body, and the arrangement being characterised in that the axis of the screw runs substantially parallel with the adjacent blade flank and in that the screw head, as it is driven home, first bears against said reaction surface and is then brought into edging engagement with the blade flank.

3. A rotary cutting tool (such as a milling cutter, a boring bar or a facing tool) having a generally circular-cylindrical body around whose cutting there is removably held a circumferentially successive number of flat-flanked multiplecutting-edge "indexable" blades, the or each such blade being housed in an accommodating recess in the body of the tool so that one flank (or, where approximate, each of the two opposed parallel flanks) of the blade extends generally radially of the tool body and the blade presents a cutting edge substantially parallel to and slightly proud of the side surface or the cutting end face (or both) of the body, characterised in that the or each blade is removably wedged into its accommodating recess by a screw whose head has a spherical side surface and which is driven into the tool body to bring said side surface into contact with an adjacent flank of the blade and so wedge the opposite flank firmly against a wall of the recess.

4. A tool according to claim 1 or claim 3, in which a side surface of the screw head bears against the adjacent blade flank, and the screw head is supported - when in wedging engagement - radially of its axis by a reaction surface of the tool body, characterised in that as the screw head is driven home it first bears against said reaction surface and is then brought into wedging engagement with the blade flank.

5. A tool according to any of claims 1,2 and 4, in which the screw head has a cylindrical side surface which bears against the adjacent blade flank, and the underside of the screw head tapers towards the axis of the screw and bears against said reaction surface.

6. A tool according to any of claims 1, 2, and 4 in which the screw head has a spherical side surface which bears against the adjacent blade flank.

7. A tool according to any of claims 1, 3, 4, 5 and 6, in which the axis of the screw runs substantially parallel with the adjacent blade flank.

8. A tool in accordance with any of the preceding claims, the tool being in the form of a facing tool and having a circular-cylindrical pilot projecting forwardly of the cutting blades, characterised in that the diameter of the pilot overlies the adjacent radially innermost corner of the or each blade.

9. A tool in accordance with any of the preceding claims, characterised in that, a wedge for example, a cone - is housed centrally and longitudinally at the cutting end of the tool body and has a longitudinal surface which contacts the radially innermost edge of the or each blade, and in that there are provided means for advancing the wedge progressively axially up and down the tool body (i.e. towards and away from the cutting end) so as to move the or each blade progressively radially inward and outward when the blade is not clamped in position by its associated clamping screw.

10. A tool according to claim 9, characterised in that the wedge is advanced against the action of a spring.

11. A tool according to claim 9 or claim 10, characterised in that means are provided to lock the wedge directly against the tool body when the or each blade has been advanced to its desired radial setting.

12. A rotary cutting tool substantially as described herein with reference to, and as illustrated in, the accompanying drawings.