Facts and Suggestions About Trimming Knives
The right-hand knife must be adjusted so that its edge is exactly parallel with the left-hand knife in order to make the slug of equal thickness throughout its entire length. The faces of the two knives separate slightly toward the front of the machine, which allows the slug to pass freely forward from the cutting edges. The right-hand knife must be shaped so there is a cutting edge of about 1/64 of an inch on the side that stands next to the slug. By having this edge the “gouging” of the knife into the slug is prevented, and slugs are trimmed to equal thickness at the top and bottom. This cutting edge must never be more than 1/64 of an inch.
Always remember that the knives can be set to trim the slugs perfectly from one point-size to another with accuracy, but it requires patience, as the knives must be adjusted to a thousandth part of an inch.
Keep the knife block and the knives clean. The seat of the knives should also be clean. It will be impossible to get an accurate adjustment if dirt or gum interferes with the movement of the knives.
The trimming knives should have exceedingly sharp or thin edges to work satisfactorily. If the knives become very dull or the cutting edge rounded or nicked, they should be taken off the machine and reground. Send them to the nearest agency as they are equipped with grinders and other fixtures to do this regrinding and maintain the correct angles and shape of the knives. Always send both the right-hand and left-hand knives, as they should be reground in pairs, and the cutting edges should exactly match each other in order to obtain good results.
Use a full measure slug when adjusting the trimming knives. Cast a full line of capital letters on the slug and hold the matrices for recast. Measure the slug on the ribs at the top and near the bottom. The slug should measure the same at the top edge and near the bottom if the knife which trims the smooth side is correctly set. The slug should measure the same at the top edge of both ends if the knife which trims the rib side of the slug is correctly set.
Before setting the trimming knives, make sure that the mold is properly seated in the mold disk and that there is no metal between the liners and the mold.
When the trimming knives become dull it is practically impossible to set them to trim accurately. Even when they are set nearly accurate, they will hold the adjustment only a short time.
Dull knives also cause trouble by making it difficult to eject the slug. This will often cause the clutch to slip.
When a long slug measures thicker or thinner at the ends than in the center, it is usually due to dull knives, but may be caused by the knives being forced in a twist or strain by the adjusting screws or some foreign substance behind the knives.