GB2040743A

GB2040743A - Machining elongate magnetic articles

Info

Publication number: GB2040743A
Application number: GB7924650A
Authority: GB
Original assignee: Gerber Scientific Instrument Co
Current assignee: Gerber Systems Corp
Priority date: 1979-02-01
Filing date: 1979-07-16
Publication date: 1980-09-03
Also published as: FR2447777A1; JPS55106757A; DE2935829A1

Abstract

An axially elongated magnetic workpiece (W) is supported along a portion of its length within an elongated trough in a magnetic chuck (12). The chuck is energised to hold the workpiece in the trough and the workpiece rotated about its axis while a rotating grinding wheel (46) travels longitudinally relative to the rotating workpiece to form a helical groove in the workpiece. <IMAGE>

Description

SPECIFICATION Machining elongated magnetic articles This invention relates in general to method and apparatus for machining elongated articles and deals more particularly with an improved method and apparatus for machining axially elongated magneticworkpieces. It is the general aim of the present invention to provide an improved method and apparatus for precision machining of long, slender articles of generally cylindrical form such as, for example, helical reamers and twist drills.

In accordance with the present invention there is provided a method for machining an axially elongated magnetic workpiece, which comprises supporting the workpiece with at least a portion of its length in engagement with a work holder and for rotation relative to the work holder, applying magnetic force to the workpiece to hold it in engagement with the work holder, rotating the workpiece about its axis and relative to the work holder while the workpiece is held by said magnetic force, engaging a machine tool with the workpiece, and moving the machine tool and workpiece in machining engagement relative to each other as the workpiece rotates relative to the work holder.

Further according to the present invention there is provided apparatus for machining an axially elongated magnetic workpiece which comprises means capable of axially rotating the workpiece, a work holderwhich supports the workpiece with at least a portion of its length in engagement with the work holder, means capable of applying a magnetic force to the workpiece to hold the workpiece in engagement with the work holder, and a machine tool to machiningly engage the workpiece as the workpiece is rotated and held by the work holder.

Still further, in accordance with the present invention, there is provided an axially elongated magnetic workpiece when machined by the method or on apparatus as described in a respective one of the two immediately preceding paragraphs.

Preferably, but not essentially, the rotating workpiece is moved relative to the machine tool, and, further, the work holder comprises a magnetic chuck which is energised to apply the magnetic force to the workpiece.

One embodiment of apparatus in accordance with the invention, and a method of performing the invention, will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a somewhat schematic elevational view of apparatus for grinding a tapered reamer in accordance with a method of the present invention; Figure 2 is a somewhat schematic fragmentary plan view of the apparatus of Figure 1; Figure 3 is a somewhat enlarged sectional view taken along the line 3-3 of Figure 1 and Figure 4 is a sectional view taken along the line 4-4 of Figure 3.

Turning to the drawings and referring first particu marly to Figures 1 and 2, the apparatus illustrated is somewhat schematic and indicated generally by the reference numeral 10. The apparatus 10 is particularly adapted for machining an elongated workpiece W and includes a work holder or magnetic chuck 12 which engages and supports the workpiece W along at least a portion of its length while simultaneously applying magnetic force to the workpiece to retain it in engagement with the magnetic chuck. The drawings further include a rotary drive member 14 capable of rotating the workpiece W about its axis and relative to the magnetic chuck 12, and a machine tool or grinder 16 in machining engagement with the workpiece. The illustrated apparatus is particularly adapted to form one or more helical grooves or flutes in the workpiece W, as in making a helical reamer or twist drill.

The arrangement for driving the apparatus may vary; however, the apparatus 10 is shown set up in a numerically controlled milling, drilling and boring machine, indicated generally at 18. The illustrated machine 18 comprises a Bridgeport CNC Milling, Drilling and Boring Machine, marketed by Bridgeport Machines Division of Textron, Inc., Bridgeport, Connecticut, United States of America, and includes a quill 20, which carries a rotary spindle (not shown) and a Z axis stepping motor 22. The machine 18 further includes a reciprocally movable table 24 and step drive motors 26 and 27 for reciprocally moving the table 24 in longitudinal and transverse directions, respectively indicated by directional arrows in Figure 2. A manual control (not shown) may be used to raise or lower the table 24 to move it toward or away from the quill 20. A programmable controller 28 is provided and may be used to control the step motors 22, 26 and 27 and the quill 20. However, the step motor 27, which imparts transverse movement to the table 24 is not normally used in practising the method herein described.

The magentic chuck 12 includes two elongated pole pieces 30 separated by a longitudinal air gap 32 which is filled with brass or other non-magnetic material. Along the air gap the adjacent edges of the pole pieces 30 are shaped to form an upwardly opening trough 33, which preferably has a generally V-shaped cross-section. The air gap 32 is located at the bottom of the trough, the sides of the trough being defined by the two pole pieces, as best shown in Figure 3. The pole pieces 30 are magnetically connected by an intermediate, longitudinally extending piece of magnetic material, indicated at 34 and supported on a non-magnetic base 36. An electrical coil 38 is wound around the intermediate piece 34 and has convolutions which extend lengthwise of the air gap. The coil 38 is embedded in a suitable potting material, such as a plastics or epoxy compound.

The rotary drive member 14 comprises a rotary chuck connected to the step drive motor 22 by a flexible drive connection 40. The workpiece W, which is supported within the trough 33, is coupled to the rotary chuck 14 by an elongated somewhat flexible drive shaft 42 and a coupling member 44.

The illustrated grinder 16 is mounted on the quill 20 and comprises a grinding attachment which includes a motor for driving a peripherally-shaped grinding wheel 46 at high speed, such as, for example, 40,000 RPM.

When the apparatus 10 is used to cut one or more helical grooves in a cylindrical workpiece, as in making, for example, a twist drill, the workpiece is coupled to the rotary chuck by the drive shaft 42 and the coupling member 44 and supported along at least a portion of its length within the trough 33. The magnetic chuck 12 is then energised, applying magnetic force to the workpiece to hold it in the trough 33. While the workpiece is rotated about its axis by the rotary chuck 14 and held within the trough by the magnetic force of the chuck 12, the table 24, and hence the rotating workpiece, are moved longitudinally relative to the grinding wheel 46 with the latter in machining engagement with the workpiece, to form one or more helical grooves in it, as required, to make a twist drill. The controller 28, which is setup to control the step motors 22 and 26 is programmed to cause relative longitudinal movement between the grinder 16 and the workpiece in timed relation to the rotation of the workpiece. The controller may, if desired, also be programmed to control the quill 20 to move the grinder 16 generally toward the workpiece, as required, to form a groove of desired depth. Alternatively, the table 24 may be moved manually toward the grinding wheel to obtain the desired depth of cut. Clearly it is possible to move the grinder 16 rather than the table 24 and workpiece W.

When the apparatus 10 is used to finish the surface of a cylindrical workpiece, the diameter of the workpiece is slightly reduced as the machine tool or grinder advances longitudinally relative to the workpiece, which normally results in some slight clearance between the workpiece and the surface of the trough 33. However, the elongated drive shaft 42 is sufficiently flexible to allow the workpiece W to be drawn into the trough 33, by the magnetic force exerted by the chuck 12 and to a position of tangential engagement with the associated side surfaces of the trough, so that the workpiece remains supported or backed-up along at least a portion of its length during the machining operation.

If the workpiece W is to be ground with a taper, as in making a tapered helical reamer, the relative vertical movement of the quill 20 and horizontal movement of the table 24 may be programmed to produce the desired taper or, if desired, the workpiece W may be formed with a slight taper before it is positioned in the apparatus. The chuck 12 may then be secured to the table in a slightly inclined position, to compensate for the taper of the workpiece in a manner well known in the machining art.

Claims

1. A method for machining an axially elongated magnetic workpiece, which comprises supporting the workpiece with at least a portion of its length in engagement with a work holder and for rotation relative to the work holder, applying magnetic force to the workpiece to hold it in engagement with the work holder, rotating the workpiece about its axis and relative to the work holder while the workpiece is held by said magnetic force, engaging a machine tool with the workpiece, and moving the machine tool and workpiece in machining engagement relative to each other as the workpiece rotates relative to the work holder.

2. A method as claimed in claim 1 wherein the workpiece is supported along at least said portion of its length within a trough in the work holder.

3. A method as claimed in either claim 1 or claim 2 wherein the work holder comprises a magnetic chuck and the magnetic force is applied to the workpiece by energising the chuck.

4. A method as claimed in any one of the preceding claims wherein the relative movement between the workpiece and the machine tool is in timed relation to the rotation of the workpiece.

5. A method as claimed in any one of the preceding claims wherein the machine tool comprises a grinder having a rotatable grinding wheel which is machiningly engageable with the workpiece.

6. A method as claimed in claim 5 wherein the relative movement between the grinder and the workpiece is carried out with the axis of the grinding wheel inclined relative to the axis of the workpiece.

7. A method as claimed in any one of the preceding claims wherein the relative movement between the rotating workpiece and the machine tool when they are in machining engagement comprises moving the workpiece.

8. A method for machining an axially elongated magnetic workpiece substantially as herein described with reference to the accompanying drawings.

9. An axially elongated magneticworkpiece when machined by the method claimed in any one of the preceding claims.

10. Apparatus for machining an axially elongated magnetic workpiece which comprises means capable.of axially rotating the workpiece, a work holder which supports the workpiece with at least a portion of its length in engagement with the work holder, means capable of applying a magnetic force to the workpiece to hold the workpiece in engagement with the work holder, and a machine tool to machiningly engage the workpiece as the workpiece is rotated and held by the work holder.

11. Apparatus as claimed in claim 10 which includes means capable of moving the rotating workpiece and the machine tool relative to each other as they are in machining engagement.

12. Apparatus as claimed in claim 11 in which the rotating workpiece and the machine tool are movable relative to each other in timed relation to the rotation of the workpiece.

13. Apparatus as claimed in claim 11 orclaim 12 in which the work holder is mounted on support means which is movable relative to the machine tool to provide said movement between the rotating workpiece and the machine tool.

14. Apparatus as claimed in any one of claims 10 to 13 in which the work holder comprises a trough within which at least the said portion of the length of the workpiece is held.

15. Apparatus as claimed in any one of claims 10 to 14 in which the work holder comprises a magnetic chuck which is energised to apply the magnetic force to the workpiece.

16. Apparatus as claimed in claim 15 in which the magnetic chuck comprises two elongated pole pieces having adjacent longitudinal edges which support the workpiece and an intermediate piece of magnetic material with which the pole pieces are in engagement and around which is wound an electric coil.

17. Apparatus as claimed in any one of claims 10 to 16 in which the workpiece rotating means comprises an elongated flexible drive shaft and means for coupling the drive shaft and workpiece substantially in axial alignment.

18. Apparatus for machining an axially elongated magnetic workpiece, substantially as herein described with reference to the accompanying drawings.

19. An axially elongated magneticworkpiece when machined on apparatus as claimed in any one of claims 10 to 18.