GB2110576A - Metal cutting form tools - Google Patents

Abstract

A flat form tool, for lathe work, has a replaceable cutting tip 15 releasably secured to an elongate body 12. The body 12 comprises a profiled portion 20 and a further portion 22 shaped to provide a longitudinal reference face 23, which is abutted by a datum abutment member 14 secured to the body 12 so as to project beyond an end face shaped to provide teeth 30 which interengage with teeth 54 on a body engaging face of the cutting tip. The teeth 30, 54 are arranged to permit the tip to be slid relative to the body when the fastener 18 is released to allow a datum abutment face 55 of the tip to abut the member 14 for setting up the tool. A swarf recess 31 may be provided. <IMAGE>

Description

SPECIFICATION Metal cutting tools This invention concerns form tools for cutting metal upon a lathe.

Certain known form tools are each formed from a single elongate piece of tool steel by grinding to provide a cutting face at one end of the piece and a desired cutting profile which extends longitudinally of the piece from the cutting face so that a cutting edge or edges are defined at the junction of the profile and the cutting face. Such tools are hereinafter referred to as "flat form tools".

Such flat form tools have been known for a long time without any improvement being made, except in so far as improved tool steels have been developed over the years, and certain particular high speed steels are predominantly employed.

These particular high speed steels are selected from a wider range of high speed steels to give a particular compromise between the mutually conflicting requirements for:~ a) hardness, for cutting performance and wear rate; b) strength, e.g. tensile strength; and c) ease of grinding to a particular profile specification.

In order to enable such a tool to have a reasonable working life it is necessary to continue the profile for a substantial length along the tool, and since dimensional cutting tolerances limit the maximum and minimum dimensions of the profile, the clearance angle along the profile has to be made minimal, so that the tool can be reground several times to provide fresh cutting faces before the point along the length of the tool is reached whereat the profile provides the minimum cutting dimensions for the cutting edge.

Thus, the known tools are the subject of several compromises and constraints which are very well known. For example, small clearance angles of about 0 30' are common to give a great length of profile between the maximum and minimum profile dimensions, but such a small clearance angle gives rise to wear for some distance along the profile from the cutting edge, necessitating the removal of a considerable portion from the cutting end of the tool during re-grinding with the risk of overheating of the tool if the grinding is hurried.

The difficulty of grinding the profile to exact dimensions and taper for clearance along said length makes necessary the use of a steel which can be ground without giving rise to prohibitive expense, surface imperfections and excessive grinding wheel wear; and this precludes the selection of steels having extremely high cutting performance. The selection is the subject of the further well established compromise between hardness and strength.

In other entirely different forms of cutting devices, e.g. milling cutters, of well established and known forms, the use of replaceable cutting inserts of steels of extremely high cutting performance supported by tool bodies of steels of great strength which are relatively easy to machine have been widely adopted for a very long time in order to avoid the compromises and constraints to which flat form tools are still subjected, and in spite of the advantages of avoiding such compromises and constraints no practically useful improvements in flat form tools have been developed to benefit from such advantages.

This lack of development is primarily due to practical and dimensional limitations imposed upon the design of flat form tools by the necessary narrow elongate form of the tools and the high loads and severe vibrations to which such tools are subjected in use, together with severe cost limitations, which give rise to extremely difficult problems.

The present invention enables said problems to be solved, and according to the present invention there is provided a form tool which comprises a cutting tip element mounted upon a body, characterised in that: (a) the body is of elongate form, has a tip receiving end; a first longitudinal portion which is shaped to a predetermined profile along at least part of its length from the tip receiving end; and a second longitudinal portion which is remote from the first longitudinal portion and which provides a longitudinal datum parallel to said profile; (b) a datum abutment member is secured to said second longitudinal portion so as to overhand said tip receiving end to provide a continuation of said datum; (c) the cutting tip element has a first part provided with a cutting profile and remote therefrom a second part shaped to abut said abutment member at said datum; and (d) a threaded fastener secures said cutting element to said tip receiving end to cause interengagement between shaped interengaging faces of the end and element.

Said shaped interengaging faces may be shaped to engage in tongue and groove manner or may be serrated to provide V-shaped interengaging teeth, so that, when the fastener is released, the element may be slid, in engagement with the body, towards and away from the datum provided by the overhanging abutment member.

The cutting profile may have a clearance angle of at least 10, and preferably has a clearance angle of 20 to 30.

A swarf recess is preferably provided in the tip receiving end of the body adjacent the abutment member.

The predetermined profile preferably has the minimum dimensions and shape of the cutting profile to provide backing for the whole of the cutting profile, but may have a simplified easy to grind shape of lesser dimensions.

The invention will be described further, by way of example, with reference to the accompanying diagrammatic drawings, wherein:~ Figure 1 shows a flat form tool of the invention in side elevation; Figure 2 shows the tool in end elevation; and Figures 3, 4 and 5, shows sections through the tool on the lines Ill, IV and V respectively, shown in Figure 2.

The tool comprises a body 12, a datum abutment member 14, a cutting tip element 15 and several fasteners 17 and 18.

The body 12 is of narrow elongate form and is machined and ground from a tough steel such as EN 24 which is relatively easy to grind. The body comprises a first longitudinal portion 20 on which a longitudinally uniform profile 21 is ground; a second longitudinal portion 22 on which a datum in the form of a flat reference face 23 is ground so that the profile 21 is parallel therewith; and a tip receiving end 24.

The tip receiving end has a tip engaging face which is serrated to provide V-shaped teeth 30 which extend in parallel from the portion 20 to the portion 22 so as to be transverse to the datum, which teeth 30 terminate at a swarf recess 31 provided in the portion 22.

The abutment member is machined from a similar tough steel so as to provide a face 40 complementary to the face 23, and is secured to the portion 22 by two fasteners 17 so that a portion 41 overhangs the end 24 to continue the datum beyond the body 12.

The cutting tip element 15 has a cutting face 50 transverse to a cutting profile 52, provided on a first part 51, so as to define therewith a shaped cutting edge 53; and has a body engaging face which is serrated to provide V-shaped teeth 54 which extend from said first part 51 to a datum abutment face 55 provided on a second part 56 remote from the first part 51. The cutting element 15 is provided with an aperture which accepts and provides clearance 57 around the shank of the fastener 18 which engages in the body 12 to clamp the tip engaging face to the body engaging face so that the teeth 30. 54 interdigitate.

The cutting profile 52 is ground with reference to the datum abutment face 55 so that, when the latter abuts the face 40 on the portion 41, the profile 52 is correctly positioned with respect to the profile 21, thus obviating any need (such as there is in setting up milling cutters) for skilled labour and precision measuring or aligning devices when fitting the cutting tip element 15 to the body 12.

Said clearance 57 and the serrated interengagement between the element 15 and body 12 permit the faces 40 and 55 to be brought into positive abutment by sliding movement of this element in a specific direction towards the member 14 whilst the fastener 1 8 is in partially released position prior to the fastener 1 8 being tightened; and said interengagement prevents any movement in any direction other than said specific direction particularly when the fastener 18 is tightened, thus, in combination with the positive abutment, obviating any need for the fastener 18 to resist working loads transverse to the axis of the fastener.

The obviation of such needs gives great cost and working advantages, which are additional to the advantages mentioned hereinbefore which can be obtained by forming the cutting element 15 from a steel having great cutting performance, e.g.

high speed steel T1 5. Such steel can be used because the length of the cutting profile is relatively very short compared with the body profile length, even though it is slow and difficult to grind. Furthermore, the clearance angle A (Figure 3) can be relatively large, e.g. 20 or more, due to the shortness of the cutting profile, thus reducing wear behind the cutting edge and reducing the amount of regrinding necessary to renew the cutting edge to 50% or less of the amount necessary with known flat form tools.

The invention enables cost economies to be made, e.g. wastage is reduced because the cutting elements are small and the body constitutes the bulk of the tool, the amount of expensive high speed steel needed for cutting is much less, and the body can be left in position in the lathe when a worn cutting element is quickly replaced by a sharpened cutting element enabling production on the lathe to rapidly be resumed.

Claims (10)

1. A form tool comprising a cutting tip element mounted upon a body, characterised in that: (a) the body is of elongate form and comprises a tip receiving end; a first longitudinal portion shaped to a predetermined profile along at least part of its length from the tip receiving end; and a second longitudinal portion which is remote from the first longitudinal portion and which provides a longitudinal datum parallel to said profile; (b) a datum abutment member is secured to said second longitudinal portion so as to overhang said tip receiving end to provide a continuation of said datum; (c) the cutting tip element has a first part provided with a cutting profile and remote therefrom a second part shaped to abut said abutment member at said datum; and (d) a threaded fastener secures said cutting element to said tip receiving end to cause interengagement between shaped interengaging faces of the tip receiving end and tip element.

2. A form tool as claimed in Claim 1, wherein said shaped interengaging faces are shaped to permit the tip element to be slid in engagement with the tip receiving end only in predetermined directions towards and away from said datum, when the fastener is released.

3. A form tool as claimed in Claim 1 or 2, wherein said interengaging faces are serrated to provide interengaging teeth which extend towards said datum.

4. A form tool as claimed in Claim 1,2 or 3, wherein a recess is provided in the tip receiving end of the body adjacent to the abutment member.

5. A form tool as claimed in Claim 4 as appended to Claim 3, wherein said teeth on the tip receiving end terminate at the recess.

6. A form tool as claimed in any preceding claim, wherein the cutting profile has a clearance angle of at least 10.

7. A form tool as claimed in Claim 6, wherein said clearance angle is within the range of 20 to 30.

8. A form tool as claimed in any preceding claim, wherein the predetermined profile has the minimum dimensions and shape of the cutting profile.

9. A form tool as claimed in any preceding claim, wherein the body is formed from a tough steel, such as AN 24, and the tip is formed from a high speed steel, such as T1 5.

10. A form tool substantially as hereinbefore described with reference to the accompanying drawings.