GB2419562A

GB2419562A - Honing blind bores

Info

Publication number: GB2419562A
Application number: GB0524135A
Authority: GB
Inventors: Thomas Brown
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-01-15
Filing date: 2005-11-28
Publication date: 2006-05-03
Anticipated expiration: 2025-11-28
Also published as: GB0500824D0; GB0524135D0; GB2419562B

Abstract

A method of honing a blind bore 2 using a mandrel 3 comprising a shaft 4, one or more honing elements 9 at or adjacent one end of the shaft 4, one or more rubbing elements 6 provided on the shaft 4 and an adjustment mechanism 13 at least partially located in a longitudinal groove (7, fig. 2) extending along the shaft 4 and by which the honing element(s) 9 can be radially moved relative to the shaft 4. The end of the shaft 4 with the honing element(s) 9 is inserted into the bore 2 with the honing element(s) adjacent its blind end. Then the adjustment mechanism 13 is operated to move the honing element(s) 9 into contact with the bore wall. The mandrel 3 is then rotated and simultaneously withdrawn. If necessary these steps are repeated until a desired bore diameter is achieved.

Description

IMPROVEMENTS RELATING TO HONTNG MANDRELS

The present invention relates to a method of honing a small bore closed passageway in a metal block, and to a honing mandrel for use in such a method.

The term small bore closed passageway' is defined as a passageway having a diameter of no more than or equal to 15 millimetres, and typically no more than or equal to 10 millimetres, which has a depth greater than or equal to 35 millimetres, and which is closed or bottoms out at a distal or remote end thereof.

In fuel injection systems, precisely honed passageways in metal blocks are essential. A standard known honing mandrel for precision honing of passageways in metal blocks has a shaft which (on its operating portion) carries longitudinal rubbing strips and a groove to receive a rubbing stone. This rubbing stone can be moved out by a desired amount to determine the required precise internal diameter if the passageway and extends for the whole length of the working part of the shaft. In use the rubbing stone is adjusted so that it projects to the desired extent and the mandrel is then driven inwardly (while rotating) in order to hone the passageway from the top to the base thereof.

However, when the passageway is relatively narrow it is difficult, if not impossible, to hone the passageway precisely beyond a certain depth because the shaft tends to bend off line at the bottom end as the depth of the shaft into the passageway increases. It is an object if this invention to try to reduce this problem so that the accuracy of honing to the desired full depth of the passageway can be increased.

According to a first aspect if the invention, there is provided a method of honing a small bore closed passageway, as hereinbefore defined, in a metal block, the method comprising the steps of: a) selecting a mandrel having a diameter suitable for honing the small bore passageway to a predetermined diameter, the mandrel comprising a shaft, a rubbing stone at or adjacent to one end of the shaft, one or more rubbing elements, and an adjustment mechanism by which the rubbing stone can be radially moved relative to the shaft; b) inserting said one end of the shaft of the mandrel into the small bore passageway to be honed; c) operating the adjustment mechanism to move the rubbing stone into contact with a wall of the small bore passageway; d) rotating the mandrel; and e) withdrawing the rotating mandrel from the passageway, so that the small bore passageway is honed by the rubbing stone as the mandrel is extracted.

Preferably, steps (b) to (e) are repeated until the predetermined diameter of the passageway is achieved.

According to a second aspect of the invention, there is provided a honing mandrel for a method in accordance with the first aspect of the invention, the honing mandrel comprising a shaft having an end for location in a small bore closed passageway to be honed, one or more rubbing elements provided on the shaft, a longitudinal groove displaced circumferentially relative to the rubbing element and extending along at least part of the shaft from or adjacent to said end, an adjustment mechanism provided at least in part in the longitudinal groove, and a rubbing Stone movable radially relative to the shaft by the adjustment mechanism, the rubbing stone only extending a short distance from or adjacent to the said end of the shaft Preferable and/or optional features of the second aspect of the invention are set forth in claims 4 to 12, inclusive When using the honing mandrel if this invention, because there is only a small length of rubbing stone (as compared with a conventional honing mandrel) and the honing operation is carried out from the base of the small bore closed passageway progressively up to the open end, there is little or no tendency for deviation of the shaft from the axis of rotation, because of the rubbing stone being progressively ground down. Thus, a desirably smooth and accurate finish throughout the whole of the passageway can be achieved.

It should be appreciated that the term "rubbing stone" is intended to cover any block of a suitable grinding material which might conventionally be utilised in honing mandrels The rubbing stone is conventionally secured to a mounting block which sits within the groove in the shaft. An existing honing mandrel for conventional use can be modified by removing the top portion of the rubbing stone from the block, thus leaving the required short section of rubbing stone at the lower end portion only of the shaft The invention may be performed in various ways and a preferred example thereof will now be described, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a cross section through a passageway in a block which is to be honed by a mandrel in accordance with the second aspect of the invention; Figure 2 is a cross section through an end portion of the mandrel of Figure 1; Figure 3 is a vertical section through the block at an intermediate stage of honing; and Figure 4 is an exploded view of an adjustment mechanism within the mandrel of Figure 1.

In Figure 1 there is shown a metal block 1 into which a passageway 2 has been roughly drilled leaving an internal surface which needs to be precisely honed The passageway is a small bore passageway, typically having a diameter of no more than or equal to 15 millimetres, and preferably a diameter of no more than or equal to 10 millimetres. The passageway is closed at the distal or remote end, and is thus not a through-passageway.

The passageway has a depth of greater than or equal to 35 millimetres, preferably being greater than or equal to 38 millimetres, and which can typically extend for 100 millimetres or more. Conventional mandrels can be used for honing closed passageways of up to 35 millimetres, but after this depth, deviation of the conventional mandrel occurs, leading to imperfect honing.

To hone the closed small bore passageway, a honing mandrel 3 is presented into the passageway 2. A shaft 4 carries one or more longitudinal rubbing strips 6 (see also Figure 2), which commence at 5, being typically greater than a quarter of the length of the mandrel, and there is also a longitudinal groove 7 running along the shaft 4 which receives a mounting block 8, the tip of which carries a rubbing stone 9. The rubbing stone 9 extends only a short distance along the longitudinal extent of the shaft 4 from a point at or adjacent to the distal end of the mandrel 3, and typically extends a distance which is equal to or less than a quarter of the length of the shaft. The rubbing stone 9 extends only partway along the mounting block 8, and typically only extends a distance which is less than or equal to half the length of the mounting block 8.

The rubbing stone 9 project radially away from the shaft 4, and in use works against the side walls of the passageway 2 as the mandrel 3 is rotated. At the same time, the mandrel is progressively withdrawn from the passageway with the result that a smooth and accurate finish to the passageway is achieved. As shown in Figure 3 the mandrel has been withdrawn partially so that the lower portion 2A of the passageway now has the required smooth finish, whilst portion 2B of the passageway still requires polishing by the rubbing stone 9 during further withdrawal of the mandrel 3.

The mounting block 8 is shown in more detail in Figure 4. As can be seen the rubbing portion 9 extends along only part of the length of the mounting block 8. At one side of the mounting block 8, part of the material is removed to create a cam surface 10 leading to a stop projection 11 and a further cam surface 12. An adjustment plate 13, which has a length matching or substantially matching the length of the shaft 4, is shaped so as to provide a cam surface 14 corresponding to the surface 10, a stop 15 which can abut against the stop 11 and a further cam surface 16 to correspond to the surface 12. Both the mounting block 8 and the adjustment plate 13 are located within the groove 7 with the plate 13 nesting within the cut away surface to the one side of the block 8. The adjustment plate 13 can be moved in the direction of the arrow 17 by a user of the mandrel so that the two cam surfaces 14 and 16 act against the cam surfaces 10 and 12 on the block 8, this altering the amount by which the rubbing stone 9 projects from the groove 7.

The amount of projection of the rubbing stone 9 of course determines the diameter to which the passageway is honed. Mandrels of differing diameters are available, and an appropriate mandrel for the required diameter of passageway is selected prior to honing.

At the preliminary stages of honing, with the selected mandrel 3 engaged with a rotating machine and the lower or distal end of the shaft 4 inserted and at the base of the passageway 2, the rubbing stone 9 may have to be eased out progressively, whilst the mandrel 3 is rotated, until the desired diameter is achieved for the passageway 2. The mandrel can then be steadily removed from the passageway 2 so that the rubbing stone 9 hones the remainder of the passageway. The or each rubbing strip buffers the passageway surface to prevent undue wobble or deviation of the mandrel. The upper end of the rubbing stone 9 may be worn away with time, but the lower end of the rubbing stone will still be present to ensure precision of honing as the honing operation progresses. This is in contrast to the conventional method of honing where a rubbing strip extends for the whole length of the block 8 and is moved downwardly into the passageway 2, whilst the mandrel 3 is rotated This means that the lower end of the rubbing stone 9 tends to become worn When the lower end of the shaft 4 reaches the bottom of the passageway, it is thus impossible for the worn end of the rubbing stone to hone the lower portion of the passageway accurately to the desired dimensions.

Furthermore, the worn leading edge of the rubbing stone tends to deviate the mandrel away from the true path, resulting in a misaligned passageway As shown in Figures 1 and 3, the lower end of the shaft 4 typically includes a cap 18 which caps the groove 7 and prevents the mounting block 8 from sliding longitudinally out of the groove 7. The cap 18 sits against the bottom of the passageway prior to commencement of the honing operation. This means of course that the very bottom end of the passageway will not be honed, but the depth of the passageway will be created such that the portion of the passageway that is honed in the operating region of the passageway in subsequent use.

Other type of rubbing element, additionally or alternatively to rubbing strips, can be utilised. For example, a single rubbing strip can be utilised, or a rubbing buffer can be formed partially around the circumference of the lower portion of the shaft. When two rubbing strips are utilised, the angular displacement is typically equiangular at 120 degrees, leaving 120 degrees angular spacing between each strip and the rubbing stone.

The embodiments described above are given by way of examples only, and modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method of honing a small bore closed passageway, as hereinbefore defined, in a metal block, the method comprising the steps of: a) selecting a mandrel having a diameter suitable for honing the small bore passageway to a predetermined diameter, the mandrel comprising a shaft, a rubbing stone at or adjacent to one end of the shaft, one or more rubbing elements, and an adjustment mechanism by which the rubbing stone can be radially moved relative to the shaft; b) inserting said one end of the shaft of the mandrel into the small bore passageway to be honed; c) operating the adjustment mechanism to move the rubbing stone into contact with a wall of the small bore passageway; d) rotating the mandrel; and e) withdrawing the rotating mandrel from the passageway, so that the small bore passageway is honed by the rubbing stone as the mandrel is extracted.

2. A method as claimed in claim 1, wherein steps (b) to (e) are repeated until the predetermined diameter of the passageway is achieved.

3. A honing mandrel for a method as claimed in claim 1 or claim 2, the honing mandrel comprising a shaft having an end for location in a small bore closed passageway to be honed, one or more rubbing elements provided on the shaft, a longitudinal groove displaced circumferentially relative to the rubbing element and extending along at least part of the shaft from or adjacent to said end, an adjustment mechanism provided at least in part in the longitudinal groove, and a rubbing stone movable radially relative to the shaft by the adjustment mechanism, the rubbing stone only extending a short distance from or adjacent to the said end of the shaft.

4. A honing mandrel as claimed in claim 3, wherein the rubbing stone extends a distance which is significantly less than a length of the rubbing element.

5. A honing mandrel as claimed in claim 3 or claim 4, wherein the rubbing stone extends a distance which is equal to or less than a quarter of the length of the shaft.

6. A honing mandrel as claimed in any one of claims 3 to 5, wherein the rubbing element is a rubbing strip which extends along at least part of the longitudinal extent of the shaft.

7. A honing mandrel as claimed in claim 6, wherein two or more said rubbing strips are provided.

8. A honing mandrel as claimed in claim 7, wherein the rubbing strips are equi- angularly spaced around a rotational axis of the shaft.

9. A honing mandrel as claimed in claim 8, wherein two said rubbing strips are spaced by 120 degrees.

A honing mandrel as claimed in any one of claims 3 to 9, wherein the longitudinal groove extends along the whole or substantially whole longitudinal extent of the shaft.

11. A honing mandrel as claimed in any one of claims 3 to 10, wherein the adjustment mechanism includes a mounting block on which the rubbing stone is mounted, the rubbing stone extending only partway along the mounting block.

12. A honing mandrel as claimed in claim 11, wherein the rubbing stone extends a distance which is less than or equal to half the length of the mounting block.

13. A honing mandrel substantially as hereinbefore described with reference to the accompanying drawings.