[Figs. 18] and [19] illustrate the turning of an automobile flywheel, which is another typical example of work for a machine of this type. The flywheel is finished in two settings. Its position for the first series of operations is shown in [Fig. 18], and the successive order of the four operations for the first setting is shown by the diagrams, [Fig. 20]. The first operation requires four tools which act simultaneously. The three held in tool-block A of the turret, face the hub, the web and the rim of the flywheel, while tool a in the side-head rough turns the outside diameter. The outside diameter is also finished by broad-nosed tool b which is given a coarse feed. In the second operation, the under face of the rim is finished by tool c, the outer corners are rounded by tool d and the inner surface of the rim is rough turned by a bent tool B, which is moved into position by indexing the main turret. In the third operation, the side-head is moved out of the way and the inside of the rim is finished by another bent tool B1. The final operation at this setting is the boring of the central hole, which is done with a bar C having interchangeable cutters which make it possible to finish the hole at one setting of the turret.
Fig. 20. Diagrams showing How Successive Operations
are Performed by Different Tools in the Turret
The remaining operations are performed on the opposite side of the work which is held in “soft” jaws J accurately bored to fit the finished outside diameter as indicated in [Fig. 19]. The tool in the main turret turns the inside of the rim, and the side-head is equipped with two tools for facing the web and hub simultaneously. As the tool in the main turret operates on the left side of the rim, it is set with the cutting edge toward the rear. In order to move the turret to this position, which is beyond the center of the table, the center stop previously referred to is swung out of the way.
Floating Reamer Holders.—If a reamer is held rigidly in the turret of a boring mill or turret lathe, it is liable to produce a hole which tapers slightly or is too large. When a hole is bored with a single-point boring tool, it is concentric with the axis of rotation, and if a reamer that is aligned exactly with the bored hole is fed into the work, the finished hole should be cylindrical and the correct size. It is very difficult, however, to locate a reamer exactly in line with a bored hole, because of slight variations in the indexing of the turret, or errors resulting from wear of the guiding ways or other important parts of the machine.
To prevent inaccuracies due to this cause, reamers are often held in what is known as a “floating” holder. This type of holder is so arranged that the reamer, instead of being held rigidly, is allowed a slight free or floating movement so that it can follow a hole which has been bored true, without restraint. In this way the hole is reamed straight and to practically the same size as the reamer.
