GB2233265A - Cutting tool apparatus for cylindrical workpieces - Google Patents

Abstract

The apparatus, primarily for cutting thick-walled pipes, reduces vibration for a cutting insert 11 mounted in a holder 13 thin enough to follow the insert into the cut by a bracing support 15 disposed at an angle to the holder, adjustably secured at one end to a rotating assembly and supporting the holder 13 at its other end. Sliding contact is maintained by a vee 16 in the surfaces. The support 15 is thin enough to enter the cut. Two tools 11, 12 may be used, of different thicknesses, the thinner starting to advance before the thicker, and keeping that relationship throughout the cut. The thicker tool 12 cuts over only a fraction of its width, and is lightly stressed. <IMAGE>

Description

CUTTING TOOL FOR CYLINDRICAL WORKPIECES This invention relates to apparatus and a method for machining cylindrical workpieces, and particularly for cutting thick-walled pipes.

The invention is defined in the several claims appended to this specification.

The invention comprises modification to a conventional portable pipe-cutting machine having a 3600 annulus or yoke removably fixed to a cylindrical workpiece and made concentric therewith in known manner. stems rotatable within the yoke include a 3600 gear ring to which the or each tool assembly is adjustably secured. It is known to use two or more cutting tools for reasons inter alia of balance, and the the two-tool arrangement is described. Circumferential drive means are provided to give relative rotation between tools and pipe, and radial drive means to feed or advance the tools radially. Thus far, the machine is conventional.

Difficulties are experienced with cutting very thick-walled pipes, because the cutting insert holder has to follow into a deep cut, and the holder is therefore a thin extended strip of metal clamped in cantilever fashion at one end, whereas the forces acting upon it are at the distal end, leading to chatter, vibration, uneven cutting, tip-wear and breakage.

The invention provides a simple means of avoiding much of the stress-related vibration, and relieving the remainder.

In the accompanying drawings, Figure 1 is a diagrammatic view on the axis of the machining centre, showing only the features required to explain the invention.

Figure 2 is a section on A-A of Figure 1; and Figure 3 is a diagrammatic representation of the relationship between the tools and the profile of the cut.

In a typical embodiment, thick-walled pipe is to be cut by a portable machine of conventional type, but having two cutting tools disposed at 1800to each other, their longitudinal axes lying in a common plane perpendicular to the machining axis 17. The tools are adapted to be advanced toward each other to cut a pipe held centred on the said axis 17. The tools comprise carbide cutting inserts 11,12, secured to extended insert holders 13,14, clamped to mounting blocks, (not shown) which are adjustably secured to an annular gear ring (not shown) upon which the tool assemblies rotate relative to the pipe. The tool 11,13, advanced to make the first cut, is 5 mm.wide, and the second tool 12,14, is 8 mm. wide, which is the total width of the cut. Figure 1 shows the disposition of the tools in relation to axis 17. Dimension X is slightly exceeded by dimension X+.Thus, tool 12,14, starts and continues feeding at a slightly greater distance from the machining -centre than first tool 11,13, and is therefore at all times cutting a short time later and physically trailing the first tool. The rotational direction of the cuts is indicated by arrows B,C. Arrows D,E, show the direction of tool feed radially inward through the workpiece. The practical result is shown in Figure 3, where 18 is the periphery of the workpiece, and 19 the profile of a partly completed cut. Both tool heads are shown, only to visualise the size relation ship. As previously stated, they are on opposite sides of the workpiece.

The thin holder 13 is steadied by contact with an elongated metal strip support 15, disposed at 900 to the holder, removably clamped in a mounting block (not shown) adjustably secured to the gear ring at one end, and slidably supporting insert holder 13 at the other end. As holder 13 advances and the cut grows deeper into the pipe wall, the slidable contact is made at a location partway between the clamped end and the tool tip end of holder 13, preferably nearer to the tool tip end. Contact is facilitated and continued support given by the contacting surfaces being formed in a vee or other complementary mating shape, as shown in Figures 1 and 2, where a vee 16 is formed on the free end of the support 15 and on the long edge of the insert holder 13. In this embodiment, the holder is a reversible type, so the mating shape is formed on both long edges.The sliding surfaces may be lubricated with a suitable coating, e.g. silicon grease. The mounting block (not shown) for support 15 has provision for adjusting the support radially via a sliding clamp, and the block can be adjusted circumferentially with respect to the gear ring by means of a series of differently-positioned screw holes, arranged so that the support 15 may be positioned to enter the cut, and so may steady the holder 13 near to the cutting tip insert 11. In this embodiment, the second, thicker tool 12,14, does not need this form of support, but one may be provided if necessary.

The effect of the invention, as seen in Figure 3, is that the thicker tool is cutting over only a fraction of its width - in this embodiment over only 3/8 of its width, and is therefore relatively unstressed. The thinner tool cuts its full width, so is highly stressed. In a deep cut its susceptibility to vibration is reduced by the provision of a support. Thus, speedy deep cutting with reduced tool wear and breakage is achieved.

The invention is not confined to cutting pipes, and may be used on any solid or hollow workpieces of substant ially cylindrical section, such as vessels, shafts, round bar etc. It may also be used for cuts other than the straight cut perpendicular to the workpiece axis as described, e.g. to cut a taper. Its primary use is as a portable tool, but it may be used fixed in a stationary location as desired.

The support 15 has been described as disposed at 900 to the holder 13, but a support may be modified to adapt to a different angle if required, by forming its support ing end at the desired angle and suitably adjusting its mounting block.

It will be evident from the description of the support 15 being positioned to enter the cut, that the support must be sufficiently thin; that is, it must be of lesser width than the thicker tool, so that it may enter the cut as the latter deepens, and so afford optimum bracing or steadying of the thinner holder, preferably near to the tool insert end.

Claims (9)

1. A cutting tool for cylindrical workpieces, including an annulus removably secured to a workpiece; means for making it concentric therewith; a cutting tool assembly including a cutting insert held in an extended holder and adapted to advance with a radial component of direction into the workpiece; means for feeding the tool and for producing relative rotation between tool and workpiece; characterised in that the tool is slidingly supported during its advance, at a location partway along one long edge of the holder between its clamped end and the insert end, by a thin, elongated support adjustably and removably secured to the rotating assembly.

2. A cutting tool according to Claim 1, in which the support is sufficiently thin to enter the cut, that is, the support is of lesser width than the tool.

3. A cutting tool according to Claim 1 or Claim 2, in which the support slidingly contacts the holder by means of a vee or the like complementary mating shape formed in the contacting surfaces.

4. A cutting tool according to any previous claim, in which the support is disposed at 900 to the holder.

5. A cutting tool according to any previous claim, in which the support is mounted on the rotating assembly by securing means which permit adjustable positioning of the support, both radially and circumferentially.

6. A cutting tool according to any previous claim, in which at least two cutting tool assemblies are used, adapted to advance along different axes which lie in a common plane perpendicular to the machining axis, characterised in that a) the first cutting insert and holder are less wide, that is, thinner, than the second and any subsequent inserts and holders, and the radial feeding means is arranged to feed the thinner tool first, to start and continue the cut first, the thicker tool(s) being fed slightly later, to start and continue throughout to cut physically behind the cut produced by the thinner tool, in the feed direction, and b) at least the thinner tool is slidingly supported by the said support, the subject of the previous claims.

7. A method for machining cylindrical workpieces, comprising the steps of providing apparatus according to any of Claims 1 to 5; supporting the tool against vibration by sliding contact withthe said support, the subject of Claims 1 to 5.

8. A method for machining cylindrical workpieces, comprising the steps of providing apparatus according to Claim 6; radially advancing the thinner tool into the workpiece first to cut at a slightly smaller radius than the thicker tool(s); supporting at least the thinner tool throughout the operation by a support, the subject of any of Claims 1 to 5.

9. A cutting tool and a machining method, substantially as described with reference to the accompanying drawings.