Device in Back Spot Facing Tools

The present invention relates to a device in back spot facing tools of the kind comprising a spindle at one, front end portion of whch, at least one wing is arranged in a recess pivotally mounted parallel with and eccentrically with respect to the spindle about an axle, which wing at the rotation of the spindle is arranged to pivot from an inactive position within the circumference of the spindle to an active position outside it, and which at the part of the wing located outside of the spindle is provided with at least one cutting edge and/or a cutter.

Back spot facing tools of the above mentioned kind are previously known through U.S. Pat. No. 3,540,324. These tools have proved to be exceptionally good concerning both function, safety of operation and applicability. In some cases difficulties can appear when the wing during rotation is to be retracted to inactive position in order to introduce the spindle through a boring in a workpiece, the rear side of which is to be provided with a spot recess or the like. Irrespective of the rotational direction the wing will through the centrifugal force be pivoted out to an active position, and if the wing is to be retracted into a recess int he spindle, the front end surface of the wing is brought to contact with the workpiece at which normally a retraction of the wing to inactive position takes place. If the friction between the wing and the workpiece is not sufficiently high, for example if there is oil on the workpiece and/or the workpiece is smooth after the boring operation, the wing will remain in its extended position even at high pressures against the workpiece and the spindle can therefore not be passed into the boring. The retraction of the wing has up to now occured because of the friction between the front end surface of the wing and the contact surface on the workpiece outside the hole.

The object of the present invention is to provide a device in back spot facing tools which enables a safe retraction of the wing to inactive position, without making the tool more complicated or expensive. This has been provided by the fact that said pivoted part of the wing outside the spindle at least at one preferably its front end surface is designed with an inclined ramp, that the ramp in the extended position of the wing has its maximum height, as seen in the axial direction of the wing, in a portion located closest to the circumference of the spindle and is arranged to incline towards the external, curved envelope surface of the wing, and that the transition section of the ramp in the envelope surface of the wing is slightly chamfered, so that at the insertion of the spindle in a boring to a workpiece, the portion of the wing which during the rotation is pivoted outwards is in contact with the hole edge of the boring and is pivoted to the inactive position at a continued displacement in the boring.

The wing is retracted only by friction between the inclined ramp of the wing and the hole edge in the workpiece. There will be almost a line contact which will function irrespective of how smooth the surface of the workpiece about the hole may be.

FIG. 1 shows a side view of the back spot facing tool according to the invention with extended wing.

FIG. 2 shows the tool according to FIG. 1, 90.degree. rotated as compared with the side view according to FIG. 1.

FIG. 3 shows the wing of the back spot facing tool according to FIGS. 1 and 2 in a perspective on a larger scale,

FIG. 4 is a section according to the line IV--IV in FIG. 2.

FIG. 5 shows the active part of the tool in cooperation with a workpiece.

The back spit facing tool according to the invention is in essential parts similar to conventional back spot facing tools, which consist of a spindle 11, at one front end 12 of which there is arranged a recess 13, in which a wing 14 is pivotally mounted. This can swing about an axle consisting of two pivots 15,16 and arranged parallel with and eccentrically with respect to the spindle 11 from an inactive position within the circumference of the spindle to an active position in which a larger part of the wing is located outside the circumference of the spindle. The wing 14 can either in itself be designed with one or several cutting edges and/or provided with one or severals cutters 17 fixed to the front edge of the wing by means of a screw 18 or the like.

If a back spot facing operation is to be performed in a workpiece 19, which is provided with a through boring 20, a back spot facing tool is selected, the spindle diameter of which is somewhat smaller than the diameter of the boring, so that it can be passed through the boring without difficulty. The rear end of the back spot facing tool, i.e. the shank, is fixed in a boring machine or the like and is rotated in the direction opposite the cutting direction., Then the wing 14 with the cutter will be pivoted by the centrifugal force to active position with the cutter located outside the circumference of the spindle. In order to provide a safe retraction of the wing, so that it becomes located in the recess 13 in front of the circumference of the spindle, one end surface 21 of the wing 14 facing the front end 12 of the spindle is designed as a ramp 22, which inclines from the transition section between the part-cylindric envelope surface 23 of the wing and the end surface 21 of the wing in a direction obliquely upwards towards the envelope surface 31 of the spindle 11, i.e. in the shown embodiment in a direction towards the plane bearing surface 25 of the wing, where the recess 26 for the pivot 16 is arranged. The inclined ramp 22 of the extended wing thus has its maximum height close to the spindle and inclines downwards towards the envelope surface 23 of the wing, at which the transition section 29 between this and the ramp 22 is slightly chamfered. The ramp 22 preferably inclines also in the direction from the front edge 24 of the wing, where the cutter 17 is fixed, and slightly downwards, backwards towards the envelope surface 23 of the wing, so that its highest point 32 is located on the front edge of the wing.

In FIG. 4 on the front and upper end surface 21 of the wing 14 equidistance lines 30 are drawn, which show the rise of the inclination and extension as seen from above. The extension of the equidistance lines 30 coincide substantially with the curving of the spindle circumference and the hole edge 27 respectively, which means that only line or point contact is obtained at the contact of the ramp with the hole edge 27 of the workpiece 19.

When pressing the wing 14 of the baack spot facing tool against the workpiece 19 the ramp 22 will thrust against the edge 27 of the boring hole 20 (FIG. 5), which in cooperation with the inclined plane of the ramp gives the wing, which is mounted eccentrically in spindle, a pivoting movement in a direction towards the recess 13 of the spindle in cooperation with the rotation of the spindle. The inclination and extension of the ramp is so selected that the edge of the boring hole 27 is active during the whole retraction movement of the wing.

When the wing has taken its inactive position inside the circumference of the spindle the front end portion of the spindle may be passed through the boring 20 and when the entire wing is located on the other side of the workpiece 19 the boring machine is reversed so that it rotates in the cutting direction and the spot facing 28 or the like can be started by withdrawing the spindle. When the work is finished the spindle is reversed again so that it rotates in a direction opposite the cutting direction, after which the spindle is withdrawn, so that the cutter of the wing will be in contact with the back spot facing 28. This contact will causes a retraction of the wing to an inactive position. The back spot facing tool can then be withdrawn from the boring 20.

It has proved to be appropriate to desing the ramp 22 with a pitch angle of about 10.degree..

The invention is not limited to the described and shown embodiments but several modifications are possible within the scope of the claims. Thus it is possible to arrange a corresponding ramp at the bottom end surface of the wing.