Linotype mechanism

by Alvin Garfield Swank; Raymond Means

MOLD KNIFE

The mold or back knife trims the base of the slug and is fastened to the mold slide arm, back of the mold disk. It is placed at an angle of about 45 degrees and is held by two washers and two round-head screws which pass through the slotted holes of the knife. It is also held by two adjusting screws that set against the base so that the knife will set squarely and press lightly against the mold as the disk is turned from casting to the ejecting position. As the mold passes in front of the knife, the slug should be trimmed type-high, which is .918 of an inch.

The front of the mold disk, when turning, must be bearing against the mold disk guide so as to keep the mold against the knife while the slug is being trimmed. If the mold disk guide does not set snugly against the disk, the disk will spring away from the knife and the slug will be higher on one end than the other. The guide is adjusted by loosening the screw which holds it to the mold slide and moving it snugly against the mold disk. Do not set the guide tight enough to bind and prevent the free turning of the disk.

It sometimes happens that a disk will bind at one or more places as it is being turned. This is due to the disk becoming warped from heat or some other cause. If it is only a slight bind it will not interfere with the adjustment.

Whenever it is necessary to put on a new or resharpened mold knife, or to adjust it, be sure the mold disk guide is bearing against the rim of the mold disk. It is always better to remove the guide and clean it as it must be perfectly clean when it seats against the disk. Always have the knife away from the mold when seating the guide. Tighten the hexagon head screw slightly and then tap the guide until a slight pressure against the disk is secured. Turn the disk by hand until an even pressure has been secured and then tighten the hexagon head nut tight.

Place the mold knife on the knife seat; be sure the seat is clean, for the least particle of dirt or metal will make it more difficult to make the adjustment. Also the bottom of the mold must be perfectly clean and free from all metal. Set the knife square with, but not quite touching the mold. Tighten down on the two round-head screws, then adjust with the two screws under the bottom of knife so that mold will turn without binding. The left-hand end of the knife trims the ends of the slugs; the center of the knife trims the center of the slugs. Avoid excessive pressure on either side as the knife is so shaped that the sharp edge should just touch the mold.

After making sure that the guide block and the knife are properly set, cover the back of the mold with a thin coating of red lead; turn the disk and mold until the mold passes the knife. If the knife is adjusted properly, it should scrape the lead from the mold. It is not always an easy matter to set a mold knife, taking considerable patience and care because the knife must be set to thousandths of an inch. Cast a slug and measure with the micrometers to make sure the slug is trimmed to the proper height. When measuring the slug for height with micrometers, use a slug 15 picas in length, or one that fills half of the capacity of the mold. Have the regular letter characters cast on the slug.

Metal will adhere to the bottom of the mold if the mold knife is not sharp or properly adjusted. To keep a perfect lockup the bottom of the mold must be kept clean. Mold knives can be resharpened, but as they are shaped to set just so the edge of the knife touches the mold and must not vary, for even .001 of an inch will spoil the adjustment, they should be shipped to the nearest agency to be resharpened.

Be sure the knife is at fault before starting to adjust it.