GB2084527A

GB2084527A - Rail structure for machine tool

Info

Publication number: GB2084527A
Application number: GB8031824A
Authority: GB
Original assignee: BOC Ltd
Current assignee: BOC Ltd
Priority date: 1980-10-02
Filing date: 1980-10-02
Publication date: 1982-04-15
Also published as: AU7494681A; JPS5791876A; ZA815894B; US4417384A; GB2084527B; DE3138033A1

Description

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GB 2 084 527 A 1

SPECIFICATION

Improved members for supporting a movable load

The present invention relates to elongate 5 members for supporting and locating a load movable in opposite senses along the length of the members and in particular, to such elongate load supporting and locating members when they form part of a support structure for a coordinate 10 machine tool.

In this specification the expression "coordinate machine tool" is intended to embrace machine tools having a working point or surface which can be located relative to a workpiece by means of . 15 "X—X" and "Y—Y" coordinates. For the avoidance of doubt, the expression coordinate machine tool includes flame cutting machines which consist essentially of a cutting torch mounted on a carriage for movement therewith. 20 The carriage can be driven in opposite senses along a beam which in turn is mounted for movement on a pair of spaced parallel rails. The cutting torch is capable of movement in an "X—X" sense by means of the drive to the 25 carriage and in a "Y—Y" sense by movement of the beam along the rails.

The support structure, that is, the beam and rails of a flame cutting machine must be sufficiently rigid to support the load of the cutting 30 torch, the carriage and ancillary equipment associated therewith. The support structure must also incorporate locating surfaces in order that the cutting torch can be located accurately in the "X—X" and "Y—Y" planes with respect to a 35 workpiece. In flame cutting machines having a tracing width of one 1 to 2.\ metres, and a cutting width of from 0 to 2\ metres, the rails and the beam have to be of substantial rigidity and their very size and weight makes it difficult and 40 expensive for locating surfaces to be machined on these parts or attached to the parts.

For example, a pair of spaced rails on a known flame cutting machine are of the locomotive type. That is to say, they resemble the rails supporting 45 rolling stock on a railway. The rails have first to be shot-blasted for descaling purposes and then by means of a press straightened to some rough degree of alignment. They are then stress relieved to reduce rolling and bending stresses and then 50 introduced to a machine tool for planing the top and sides of each rail. It is the planing operation which produces the accurate surfaces for location purposes. Both rails are then drilled to accommodate holding down bolts and the rails are 55 then painted. In a typical operation this procedure can consume 8y hours of time.

On the same machine the beam, which is a hot-rolled box-section, is first shot-blasted and then four individual strips are first degreased, then 60 fabricated and welded to the four corners of the box-section. Although only two of the strips are used for locating purposes, four strips have to be welded to avoid distortion during the welding operation. The welds are ground flush and then

65 the strips are planed to provide accurate locating surfaces. The beam is then drilled and finally painted with the working surfaces of the strips being masked to avoid spoiling the locating surfaces. This operation can take up to 54 hours. 70 It is an aim of the present invention to provide an elongate member for supporting and locating a load movable in opposite senses along the member, which member can be incorporated into the support structure of a coordinate machine tool 75 and which is economic to manufacture when compared to known methods of manufacture.

According to one aspect of the present invention an elongate member for supporting and locating a load movable in opposite senses along 80 the length of the member comprises a first relatively rigid elongate part for supporting the weight of the movable load, a second relatively resilient elongate part for locating the movable load on the elongate member, a plurality of spaced 85 dowels extending in a straight line, the dowels engaging said first and second parts for locating said second part at a predetermined position spaced from said first part, and means for fastening the first and second parts together. 90 According to a further aspect of the present invention a method of making an elongate member for supporting and locating a load movable in opposite senses along the length of the member, comprises the steps of taking a first 95 relatively rigid elongate part for supporting the movable load and machining holes each with an associated counterbore in a straight line along the length of said first part, taking a second relatively resilient elongate part for locating the movable 100 load on the elongate member and machining holes at the same pitch distance as the holes in the first part and extending in a straight line along the length of said second part, placing a dowel in each hole in the first part, each dowel having a shoulder 105 intermediate its ends which is received by the associated counterbore of each hole and then locating said second part relative to said first part by means of said dowels, the shoulder of each dowel spacing the first part from the second part; 110 and fastening said first and second parts together.

Figure 1 is a perspective view of a flame cutting machine;

Figure 2 is a side elevation illustrating the rails forming part of the support structure of the flame 115 cutting machine of Figure 1;

Figure 3 is an end view of the rails illustrated in Figure 2;

Figure 4 is a cross-section on the line A—A in Figure 2;

120 Figure 5 is a cross-section on the line B—B of Figure 2;

Figure 6 is an elevation of a dowel forming part of the support structure; and

Figure 7 is a cross-section through a beam 125 forming part of the support structure of a flame cutting machine.

As shown in Figure 1, a flame cutting machine 1 includes a beam 2 on which is supported a carriage 3. The carriage 3 can be driven in

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opposite senses along the length of the beam by means (not shown) for locating a cutting torch at a predetermined position over a workpiece.

The carriage 3 is supported for movement 5 along two spaced parallel rails 4, 5. The rail 4 is known in the art as a secondary rail, whilst the rail 5 is known as a primary rail. The rails 4, 5 are supported on spaced pillars 7.

It will be evident, that movement of the 10 carriage 3 along the beam 2 provides a cutting torch with motion in the "X—X" plane whilst movement of the beam 2 along the rails 4, 5 provides motion of the cutting torch in the "Y—Y" plane.

15 Referring also to Figures 2 to 6, the rails 4, 5 are substantially identical but when forming part of the support structure of the flame cutting machine 1 are orientated at 90° with respect to each other (see Figure 3). The rail 5 is in the form 20 of an elongate member comprising a first relatively rigid elongate part 11 and a second relatively resilient elongate part 12. The first part 11 has a hollow box-shaped cross-section and is manufactured by cold rolling. The box-shaped 25 configuration of the cross-section gives the part 11 a high moment of inertia in the vertical or "Z—Z" plane and therefore the ability to support heavy loads without unacceptable flexure.

The second part 12 has a solid rectangular 30 cross-section and is made from precision straightened strip. The strip is resilient relative to the first part 11. The parts 11,12 are interconnected accurately with respect to each other by means of dowels 13. Each dowel 13 has 35 a first cyclindrical part 14, a second cylindrical part 15 and a shoulder 16 intermediate the first and second cylindrical parts 14,15. The free end of the cylindrical part 15 is provided with a radius 17 for reasons that will be explained later. 40 The parts 11,12 are fastened together by bolts 25, spring washers 26 and spacers 27 (see Figure 5).

When it is decided to manufacture a rail 4, 5 a first part 11 and a second part 12 each of a 45 preselected length are first degreased. Next, a first locating group of through holes 21 with associated counterbores 22 are formed in one surface of the first part 11. At the same pitch distances, blind holes 23 are also formed in the 50 second part 12. At the same time a second group of fastening holes are machined in the part 11, namely clearance through holes 31 and associated counterbores 32. At the same time a corresponding group of threaded holes 33 are 55 tapped in the part 12 at the same pitch distance as the clearance holes 31 and counterbores 32. The holes of each group in the parts 11,12 are arranged in a straight line. At this stage, the second part 12 can be treated to provide it with a 60 hard chrome surface prior to its attachment to the second part 11. Also at this stage, the part 11 can be painted.

Dowels 13 are now located in the holes 21 in the part 11 such that the first cylindrical part 14 of 65 each dowel 13 enters a through hole 21 and its shoulder 16 is accommodated by the associated counterbore 22. It will be seen from Figure 4 that the upper (as shown) surface of the shoulder 16 is at a level above that of the outer surface of the 70 part 11. It should be pointed out, that the upwardly (as shown) facing surface of the counterbore is, in effect, a datum surface and should the counterboring operation not clean up the surface of the part 11 because, for example, 75 the part 11 is distorted, then said part 11 must be rejected. The part 12 is then introduced to the part 11 such that the cylindrical part 15 of each dowel enters a hole 23 in the part 12. To this end, the radius 17 assists in locating each hole 23 over its 80 associated dowel 13. This has the effect of straightening up to an accurate degree the part 12 which prior to this time could have been slightly distorted. The fact that the part 12 is resilient compared to the part 11 enables the dowels 13 to 85 make the part 12 conform to the required straightness.

Finally, the parts 11,12 are fastened together by means of bolts 25 which pass through clearance holes 31 in the part 11 and into 90 threaded holes 33 in the part 12. Spacers 27 are provided which have substantially the same thickness as the shoulders 16 of the dowels 13 and are accommodated in the counterbores 32. The spacers 27 thereby help to maintain the 95 spacing between the part 12 relative to the part 11.

It has been found, that using the method described above, a pair of rails can be produced in just over 1 hour. The economy of manufacture is 100 startling when compared to the prior art methods of manufacture and there is no loss of rigidity or accuracy.

Referring to Figure 7, this illustrates diagrammatically a beam which can be used 105 together with the rails 4 and 5 to form a support structure for a coordinate machine. The beam differs from the rails 4, 5 only in that there are two parts 12 associated with a part 11. The method of manufacture is substantially identical to the 110 manufacture of the rails.

Claims

1. An elongate member for supporting and locating a load movable in opposite senses along the length of the member, the elongate member 115 comprising a first relatively rigid elongate part for supporting the weight of the movable load, a second relatively resilient elongate part for locating the movable load on the elongate member, a plurality of spaced dowels extending in 120 a straight line, the dowels engaging said first and second parts for locating said second part at a predetermined position spaced from said first part, and means for fastening the first and second parts together.

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2. An elongate member as claimed in claim 1, in which the first relatively rigid elongate part has a hollow box-shaped cross-section and through holes each with an associated counterbore extending along at least one surface, each hole

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with its associated counterbore receiving a portion . of a respective dowel, the second relatively resilient elongate part having a solid rectangular cross-section, one surface of which is formed with 5 holes each receiving a further portion of a respective dowel.

3. An elongate member as claimed in claim 2, in which each dowel has a shoulder between its ends, which shoulder is received within a 10 respective counterbore in said first part, a surface of the shoulder engaging said one surface of the second part thereby to locate accurately the second part at a position spaced from said one surface of the first part.

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4. An elongate member as claimed in claim 3, in which the fastening means are bolts, washers and spacers, the spacers having substantially the same thickness as the shoulder of each dowel.

5. A support structure for a coordinate machine 20 tool, comprising a beam adapted to support a carriage movable therealong, the beam being supported by a pair of spaced, parallel rails for movement of the beam in a direction parallel to the rails, the direction of movement of the beam 25 being at right angles to the direction of movement of the carriage along the beam, at least one of the rails and/or the beam consisting of an elongate member as claimed in any one of claims 1 to 4.

6. A method of making an elongate member for 30 supporting and locating a load movable in opposite senses along the length of the member, comprising the steps of taking a first relatively rigid elongate part for supporting the movable load and machining holes each with an associated

35 counterbore in a straight line along the length of said first part, taking a second relatively resilient elongate part for locating the movable load on the elongate member and machining holes at the same pitch distance as the holes in the first part

40 and extending in a straight line along the length of said second part, placing a dowel in each hole in the first part, each dowel having a shoulder intermediate its ends which is received by the associated counterbore of each hole and then

45 locating said second part relative to said first part by means of said dowels, the shoulder of each dowel spacing the first part from the second part, and fastening said first and second parts together.

7. A method as claimed in claim 6, in which

50 said second part prior to fastening to said first part is provided with a hard chrome finish.

8. An elongate member for supporting and locating a load movable in opposite senses along the length of the member, constructed and

55 arranged substantially as hereinbefore described with reference to and as illustrated in the Figures of the accompanying drawings.

9. A support structure for a coordinate machine tool, constructed and arranged and adapted to

60 operate substantially as hereinbefore described with reference to and as illustrated in the Figures of the accompanying drawings.

10. A method of making an elongate member for supporting and locating a load movable in

65 opposite senses along the length of the member substantially as hereinbefore described with reference to the accompanying drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1982. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.