GB2340057A - Reaming tool - Google Patents

Description

2340057 CUTTING TOOL This invention relates to cutting tools and in

particular to a reamer for final accurate finishing of bores in castings.

Traditionally such reamers have one cutter which is accurately positioned relative to the reamer body in order to ensure the accuracy of the finished bore. However due to the provision of only one cutter, the feed rate of the reamer is limited and this increases the cycle time of the tool which can be a significant disadvantage when high volume production is required. Also such reamers are frequently difficult to set-up which again slows production rates.

It is an object of the present invention to provide a rotary cutting tool for use in a variety of cutting operations including reaming which overcomes the above disadvantages.

Thus according to the present invention there is provided a rotary cutting tool comprising a body having a plurality of cutter support stations adjacent one end., the other end having a formation for gripping in a rotary machine tool, a central support pin located in a bore in said one end of the body, a plurality of demountable cutters each secured to a respective cutter support station in contact with said central support pin to support each respective cutter against radially inward movement during use of the tool.

Preferably the central support pin is a)dafly moveable in said bore between a first projecting position in which an outer support surfiLce of the pin, which supports the cutter when the tool is in use, can be accurately machined concentric relative to the rotational a)ds of the tool and a second retracted position in which the machined support surface of the pin is positioned to support said cutters secured to said support stations.

By enabling the support surface of the support pin to be machined in situ it is possible to ensure a high level of accuracy on the radial positioning of the support surface relative to the 2 cutter support stations thus in turn enabling the cutting edges of the cutters to be accurately positioned enabling the tool to produce high accuracy work.

The provision of a plurality of cutters (typically three) significantly reduces cycle times and the use of the accurately portioned support pin enable cutters to be changed quickly and accurately reducing set-up time.

The support pin is preferably held in its two axial positions by a grub screw in the body which contacts two axially spaced flats on the pin, one flat for each respective position.

The support pin may be provided with a circumferential extending shoulder which contacts an abutment on the body to determine the correct axial second position of the pin in the body bore.

The support pin may be provided with a removable support sleeve which surrounds the flat corresponding to the second position of the pin when the pin is in the first position to support the pin during machining of the outer surface.

The present invention also provides a method of setting up a rotary cutting tool comprising: - providing a rotary cutting tool having a body with a plurality of cutter support stations adjacent one end and a central support pin located in a bore in said one end of the body, said pin being axially moveable in said bore between a first projecting position and a second retracted position; moving said pin to said first projecting position-, rotating said body about its intended rotation axis when in use as a cutting tool and machining an outer support surface of the pin to ensure concentricity of said support surface with said intended axis of rotation of said tool; retracting said pin to said second position where the machined support surface is adjacent the cutter support stations-, and mounting cutters at said support stations supported against radially inward movement 3 during use of the tool by said pin.

In such a method the cutters may be formed with accurately predetermined dimensions prior to their mounting on the body or may themselves be machined in situ in the body for accurate positioning relative to said intended a)ds of rotation of said tool.

One embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure I is a side view of a reamer embodying the present invention; Figure 2 is a longitudinal section through the reamer of figure 1; Figure 3 is an end view of the reamer of figure I in the direction of arrow Aand Figure 4 is an end view of a modified support pin for use in the reamer of figures I to 3.

Referring to figures I to 3 a reamer 10 has a body I I at one end I I a of which three cutters 12 are secured at cutter support stations 13. Each cutter is secured at its respective work station 13 by a set screw 14 which engages a screw threaded bore 15.

The other end of the reamer I I b is gripped in a machine tool for rotation in direction X of figure I about a rotation axis Y. The cutters 12 are supported against radially inward movement relative to a)ds Y by a central support pin 16 which is located in a bore I I c in body 11.

The pin 16 is a)dally moveable within bore I I c between two alternative positions a first projecting position, shown in figure 2, in which an outer circumferential support surface 17 of the pin can be accurately machined concentric relative to the a)ds Y whilst the reamer I I is rotated about a)ds Y and a second retracted position in which the machined support surface 17 is a)dafly in line with the cutter support stations 13 and surface 17 supports the inner edges of 4 the cutters against radiaBy inward movement of the cutters during use of the reamer. This second position is best seen in figure 3 where support surface 17 can be clearly seen to support the inner edge 12a of each cutter.

To hold the support pin 16 in its two positions the pin is provided with two flats 20 and 21 which are engaged by grub screw 22 when the pin is in its projecting and retracted positions respectively. A hardened removable support sleeve 23 surrounds the support pin 16 when the pin is in its projecting position to ensure accurate support of the pin relative to the rotation axis Y. This spacing sleeve is removed prior to retraction of the support pin and a circurnferentially extending shoulder 24 on the support pin engages a shoulder 25 on the reamer body to control the axial position of the support pin in bore I I c when the pin is in its retracted working position.

As will be appreciated from the above, the fact that the support pin 16 can be machined whilst located in bore I I c ensures the accurate concentricity of support surface 17 relative to the axis of rotation Y and hence provides an extremely accurate datum against which the cutters 12 can be located when secured in the support stations 13. If desired the support surface 17 may be provided with accurately machined flats 17a (see figure 4) which are contacted by the inner edges 12a of the cutters to ensure contact over a significant area and hence improved location.

Each cutter may have a number of cutting surfaces formed at each respective comer of the cutter. For example in figure 1, the cutter 12 has two visible cutting comers 12b and 12c respectively. In the figure 1, cutting comer 12b is in the operative position and it will be appreciated that the rotation of the cutter 12 through 90' about set screw 14 enables cutting comer 12c to be indexed into the cutting position. Each cutter may have four such cutting comers greatly extending its operative life.

The cutters 12 may be purchased from a cutter manufacturer in an accurate pre-determined shape whose dimensions are accurately known which in combination with an accurately machined diameter D for the support surface 17 of pin 16 enables the position of the operative cutting comer 12b to be extremely accurately determined.

Alternatively, the cutters 12 may themselves be machined in situ in the reamer to give the particular cutter configuration required for the intended machining task. It is also possible to swap cutters between reamers in a accurately pre-determinable manner given the accuracy of manufacture of the support surface 17 of pin 16.

The present invention thus provides a multi-cutter reamer which has a high feed rate and which allows cutters to be accurately located in the reamer body in a quick and efficient manner greatly reducing the set-up time of the reamer. It is also possible to use cutters with multiple cutting surfaces which can be selectively indexed into their working positions to significantly extend the operating He of the reamer.

Although the present invention has been described above in relation to a reamer, it win be appreciated that the principle of attachment of the cutter can be used in a wide range of machine tools where accurate positioning of a cutter insert relative to an axis of rotation of the tool is required. For example the invention is particularly suitable for use in milling tools and other fine boring applications.

6 CLAMS A2607 1. A rotary cutting tool comprising a body having a plurality of cutter support stations adjacent one end., the other end having a formation for gripping in a rotary machine tool, a central support pin located in a bore in said one end of the body, a plurality of demountable cutters each secured to a respective cutter support station in contact with said central support pin to support each respective cutter against radially inward movement during use of the tool.

2. A cutting tool according to claim I in which the central support pin is axially moveable in said bore between a first projecting position in which an outer support surface of the pin, which supports the cutter when the tool is in use, can be accurately machined concentric relative to the rotational axis of the tool and a second retracted position in which the machined support surface of the pin is positioned to support said cutters secured to said support stations.

3. A cutting tool according to claim 2 in which the support pin is held in its two axial positions by a grub screw in the body which contacts two axially spaced flats on the pin, one flat for each respective position.

4. A cutting tool according to claim 2 or 3 in which the support pin is provided with a circumferential extending shoulder which contacts an abutment on the body to determine the correct axial second position of the pin in the body bore.

5. A cutting tool according to any one of claims 2 to 4 in which the support pin is provided with a removable support sleeve which surrounds the flat corresponding to the second position of the pin when the pin is in the first position to support the pin during machining of the outer surface.

7 6. A method of setting up a rotary cutting tool comprising: - providing a rotary cutting tool having a body with a plurality of cutter support stations adjacent one end and a central support pin located in a bore in said one end of the body, said pin being a)dally moveable in said bore between a first projecting position and a second retracted position; moving said pin to said first projecting position; rotating said body about its intended rotation axis when in use as a cutting tool and machining an outer support surface of the pin to ensure concentricity of said support surface with said intended a)ds of rotation of said tool-, retracting said pin to said second position where the machined support surface is adjacent the cutter support stations; and mounting cutters at said support stations supported against radially inward movement during use of the tool by said pin.

7. A method according to claim 6 in which the cutters are formed with accurately predetermined dimensions prior to their mounting on the body or may themselves be machined in situ in the body for accurate positioning relative to said intended axis of rotation of said tool.

8. A rotary cutting tool constructed and arranged substantially as hereinbefore described with reference to and as shown in the accompanying drawings.