Adjustments for Automatic Feed and Speed Changes.—The machine must now be set to perform automatically the desired changes of spindle speed and the fast and slow cam movements for the tools. After placing a new piece of work in the machine (the first one having been completed in the setting-up operation), the cam-shaft is revolved by hand until the turning tool in turret face No. 1 is just about to begin its cut. The control wheel D, [Fig. 34], is rotated in its normal direction until the next graduation marked “slow” is in line with an index mark on the base of the machine. Then the nearest pin M is moved up until it bears against a tooth of the star wheel (previously referred to) and is clamped in this position. The pin should now be in the proper location, but to test its position, rotate the cam shaft backward by hand and throw in the automatic feed; then watch the cut to see if the drum slows down just before the tool begins to work. If it does not, the pin should be adjusted a little, one way or the other, as may be required. (In going over a piece of work for the first time, it is best to have the feed set to the smallest rate, feed change handle K being in position No. 1.)
After the cut has been completed and the turret feed cam-roll is on the high part of the cam, the power feed should again be stopped and the handwheel revolved until the next graduation marked “fast” is opposite the index mark. The next stop pin is then moved up until it just touches the star wheel, where it is clamped in position. The feed being again thrown in, the turret will be returned rapidly, indexed, and moved forward for the second operation. After stopping the automatic movement, the pins are set for this face, and so on for all the operations, including that in which the cross-slide is used for cutting off the finished collar.
As the first, second, and third operations are on comparatively large diameters, they should be done at the slow speed, handle J, [Fig. 34], being set to give that speed. While the turret slide is being returned between operations 3 and 4, one of the spindle speed-changing dogs N should be clamped to the rim of disk D so as to change the spindle speed to the fast movement. This speed is continued until the last operation is completed, when a second dog is clamped in place to again throw in the slow movement. The feed knock-off dog should also be clamped in place on the disk to stop the machine at the completion of the fifth operation, when the turret is in its rear position. This completes the setting up of the machine. If the feed is finer than is necessary, the feed change handle K may now be moved to a position which will give the maximum feed that can be used.
It has taken considerable time to describe the setting up of the machine for this simple operation, but in the hands of a competent man it can be done quite rapidly. While a simple operation has been referred to in the foregoing, it will be understood that a great variety of work can be done on a machine of this type. It is not unusual to see as many as ten cutting tools operating simultaneously on a piece of work, the tools being carried by the turret, cross-slide and back facing attachment. The latter is operated from a separate cam applied to the cam-shaft and acting through levers on a back facing bar which passes through a hole in the spindle. In this back facing bar may be mounted drills, cutters, facing tools, etc. for machining the rear face of a casting held in the chuck jaws. Where extreme accuracy is required, a double back facing attachment may be used, arranged with cutters for taking both roughing and finishing cuts. The use of this attachment often saves a second operation. This automatic chucking and turning machine is also adapted for bar work, especially in diameters varying from 3 to 6 inches.
Fig. 40. Machining Flywheels in Potter & Johnston Automatic
Chucking and Turning Machine
Turning Flywheel in Automatic Chucking and Turning Machine.—A typical operation on the Potter & Johnston automatic chucking and turning machine is illustrated in [Fig. 40], which shows the machine arranged for turning the cast-iron flywheel for the engine of a motor truck. The rim is turned and faced on both sides and the hub is bored, reamed and faced on both sides. The flywheel casting is held in a chuck by three special jaws which grip the inside of the rim. The order of the operations is as follows:
The rear end of the hub is faced by the back facing bar; the cored hole is started by a four-lipped drill in the turret and the front end of the hub is rough-faced. (These tools are on the rear side of the turret when the latter is in the position shown in the illustration.) After the turret indexes, the hole is rough-bored by tool A and while this is being done, the outside of the rim is rough-turned by tool B held in a special bracket attached to the turret. Both sides of the rim are also rough-faced by tools C and D held at the front of the cross-slide, this operation taking place at the same time that the rim is turned and the hole is being bored.