Linotype mechanism

by Alvin Garfield Swank; Raymond Means

Keyboard Cams and Parts

The keyboard cams are small, brass, non-circular or eccentric pieces and are used to raise the cam yokes to operate the keyrods. The cams are pivoted and held in place in cam yokes. The outer end of the cam yokes are pivoted to the frame, while the inner ends are left free to move up or down in slots in the frame, directly underneath the keyrods.

When the cams are setting at normal, the free end of the yokes are supported by the pivoted triggers, which set directly beneath the yokes. When a trigger is moved by the keybar, it allows the free end of the yoke to drop, carrying the cam against the revolving rubber roll. The low part of the cam has small teeth cut in it, so when it drops on the revolving rubber roll, it is caused to turn. When the high part of the revolving cam is on the rubber roll, the free end of the cam yoke is raised to its highest point, raising the keyrod.

There are ninety-one cams and yokes in a keyboard. In order to get the cams in the smallest possible space, forty-five of them are located in the front frame, and forty-six in the back frame. The cam on the right-hand end of the back row is used to operate the spaceband lever.

A stop strip is fastened by means of six screws to each cam frame in such a manner that the small cross pins in the revolving cams come in contact with small pins which extend downward, stopping the cams after their revolution and holding them in normal position. The front strip has forty-five teeth and the rear strip has forty-six teeth; therefore they are not interchangeable. The strip should be located so the teeth do not bind the sides of the cams.

The top row of keys on the keyboard operate the cams in the back frame, the keys in the second row operate the cams in the front frame, the third in the back, etc., alternating for each row, so when tracing keyboard troubles it is known in which frame an offending cam will be found.

Several types of cam yokes have been manufactured for the various models of machines. Some are made of brass, others are stamped out of steel, while still another kind is milled out of a solid piece of steel. Different methods of fastening the pivoted end of the yoke have also been used. The older models were held by a pivot wire which ran through the yoke. The later models, however, have spring bars which set just above the pivoted end of the yoke, the yoke being hooked on the hinge rod and held down by a spring and plunger directly above the yoke, in the bar. This spring and plunger takes the strain off the yoke and keyrod when in an unusually heavy pull, and prevents damage to the rubber rolls.

On the top of the spring bar is an adjusting screw bushing through which the plunger projects. This plunger is forced against the top of the cam yoke by a spring. As the free end of the cam yoke raises, the spring must be strong enough to hold the pivoted end of the yoke from raising more than enough to give the full stroke of the keyrod. If something prevents the free movement of the escapement, the strain would come to the pivoted end of the yoke, forcing the plunger up, thus releasing the keyrod, cam, or rubber roll of undue strain. If this spring becomes weak, it will allow the pivoted end of the yoke to raise too high, thus lessening the up stroke of the keyrod. This shortened stroke of the keyrod does not permit the full stroke operation of the escapement, and does not allow the matrix to drop.

A weak spring will sometimes cause the matrix to drop slowly, due to the lug of the matrix binding on the lower pawl. By using the adjusting bushing this trouble can be remedied. Be careful in adjusting the spring, because too much tension will cause the cam to cut the rubber roll.

On some models the spaceband cam is of a different shape or larger than the other cams. This is done to accomplish the timing of the dropping of the spacebands.

To remove a single cam from the frame, shut off the power of the machine, take off the cover pans, touch the keybutton of the desired cam, draw out the pivot wire on old models or release the latch and tilt the spring bar on new models, turn the rubber rolls by hand until the end of the cam yoke raises, then lift the yoke and cam out.