_Safety of the Knife_
The best automatic rapid-production cutting machines are provided with four safety devices to prevent the knife making an unexpected stroke.
_First_--A solid knocker throws out the clutch positively. Neither gravity nor a spring for a trip is depended upon to move an intercepting part, but the certain fact that two solid bodies cannot occupy the same s.p.a.ce at the same time.
_Second_--An automatic friction brake grips firmly and stops all motion silently.
_Third_--An automatic counterbalance is used for both the knife-bar and the clamp, and retains them at the top position.
_Fourth_--An automatic steel safety bolt engages a solid lug on the large gear, so that the gear cannot revolve further until the operator deliberately pulls the starting lever for another cut.
These four safety devices are designed so as to act positively and simultaneously on the completion of each cut. To start requires a deliberate action of the starting lever by the operator.
_Handling Paper_
Paper is made princ.i.p.ally in long webs, or continuous strips, and is rolled up as it comes from the paper-making machine. It is then cut into sheets by a revolving fly cutter or a shear knife, cutting one sheet at a time off the roll. These sheets are furnished by the mills in bundles or cases, which are trimmed to certain sizes on a paper-cutting machine.
The best method of handling and cutting stock, the proper quant.i.ty to take on at each lift, the height of the pile to cut, and the routine of pa.s.sing each cut section along in orderly fashion, should be given careful study.
Convenient tables of the right height and of ample surface are essential if the work is to be carried on satisfactorily, without backtracking or unnecessary motions and lifting.
Large stock should be piled on movable wooden platforms which can be moved quickly from place to place.
A primary difficulty in cutting-machine work is due to the great variety of papers and sizes required to be handled on the machine. This varies from little narrow slips to piles the full width of the table, from a few sheets to a pile the full height allowed by the clamp, and from soft book paper to stock nearly as tough as tin. All these varying conditions cannot be met with equal success in one automatic machine.
Therefore, superior intelligence rather than unusual muscle should be required of the operator.
Good judgment is required to determine the proper height of a pile to cut. This will often depend upon how much can be grasped each time with the hands and put into place in good order. Time may be lost and sheets wasted trying to fill up to the capacity of the machine; smaller piles and more of them may sometimes be a more economical method. The time taken for the knife stroke is only a second, while the time necessary to jog up several lifts may be minutes more than to put one lift into place. The convenient lift, as large as possible, and uniform in size if there are several of them, is the advisable practise.
Inaccurate cutting may be the result of several causes: (a) Not jogging the pile thoroughly against the back gage; this should be done by pressing the ball of the thumbs against the front of the pile from top to bottom. (b) By disturbing the pile when turning it for the next cut.
(c) By lifting out the pile and failing to jog it carefully when flat against the back gage again. (d) Work that is fed to points on the printing press may not be square and true and consequently cannot be jogged against a straightedge gage and cut accurately. This condition should be watched for in such cases. Find out, if possible, which is the feed edge in the printing and jog up to that. Pressmen are often careless about this necessary instruction in sending printed sheets to the cutter.
Inaccurate cutting is also due to insufficient clamping pressure, allowing the pile to slip out of place slightly; or to excessive clamping pressure, compressing the pile more than necessary just at the line behind the knife cut.
The above causes may result in imperfect cutting when the machine is in good order. When the machine is not in the proper condition, and the knife is dull, or of a shape not adapted to the work, accurate cutting cannot be expected.
When piling up sheets see that each sheet is laid in exact register with all the others, that is, that the printed pages, guide marks, and edges are all in the same position throughout the pile. One sheet on top laid the wrong way may be the cause of cutting every other sheet of the pile wrong unless (and this is very important) the operator looks at the under sheets to make sure that they are all laid alike.
When cutting or tr.i.m.m.i.n.g printed sheets it is necessary that the operator should jog the sheets to the pressman"s feed edges. These should be marked plainly, without chance of misunderstanding. If they are not, he should ask for directions. One wrong cut will spoil the whole pile.
When a sheet is taken off a pile for examination or for any other purpose, care should be observed that it is laid back again uniform with the other sheets. A pile is easily disturbed in this manner either when swinging it over, turning it around, or rejogging, if the utmost care and orderliness are not observed.
Papers received from the mills or from dealers are not always trimmed squarely, but have what is called a mill edge. This edge is only approximately straight and the corners only apparently square. For accurate work, either in printing or in cutting, one or two edges may need to be retrimmed on a paper cutter to get them straight and have a true corner. The ultimate accuracy of the finished work will depend upon this proper tr.i.m.m.i.n.g before the sheets are printed.
Exact register and accurate tr.i.m.m.i.n.g can be secured only by working from the same edges of the paper at every operation and the edges must be straight and squarely cut. When the edges are thus trimmed they should be marked with a red crayon, or in some similar manner, in order to be readily identified at each handling.
A pile may be tested for squareness by jogging it in the cutter table against both the back gage and the side gage, if the machine gages are themselves in perfect adjustment. If it is difficult to see whether the sides of the pile are close against the gages at all points, narrow strips of paper put between the pile and gages will show whether the pile touches the gages uniformly.
When cutting lithographed work or similar close-register printing, where large sheets are apt to come with an irregular edge, a small wooden block against the back gage or the side gage at points on the sheet where the original register guides of the press were placed, will usually insure cutting on an accurate line with the printing. In this manner the same points of contact as were used in the press feeding may be secured.
To cut a pile of paper in half, fold over the top sheet and fold at the middle, carefully matching the edges. Crease this fold distinctly and use the crease as a guide when the sheet is opened out and laid on the pile. To cut into thirds or fifths it is better to measure the sheet exactly with a rule and make clear pencil marks at the points of cutting.
Hand-made papers have rough, uneven edges which are thicker than the rest of the sheet and, therefore, require particular care in jogging and clamping. They should be handled in small piles.
Gummed and varnished papers require special care even when perfectly dry, but more so in a moist atmosphere. Varnished stock if it is very dry may nick the knife, and a clean oily (but not too oily) swab run over the bevel of the knife before the cut will make a smoother, safer cut. It is not well to use soap on the knife, especially on lithographic work.
Freshly printed work which tends to offset on the next sheet may be cut where necessary by placing strips of reglet or thick card around the margin close to the line of the proposed cut, so as to keep the pressure of the clamp off the printed matter.
Tissue paper requires to be firmly clamped to cut accurately. A clamping motion that will first exert a gentle pressure to squeeze the air out between the sheets and pack the pile down evenly all over and then apply a powerful pressure before the knife strikes the pile, gives the best results.
Accuracy is required in manifold duplicate work, where absolute register must be made, to secure the proper location of dollars in dollars columns and cents in cents columns. The ruling and printing both depend entirely on the square and accurate cutting of the stock to secure proper register.
The cutting of waxed and oiled manifold stock, if carefully jogged up, is not difficult with the newer types of clamping mechanism, especially on that type of cutting machine where the pressure of the automatic clamp is applied at first gently and then with maximum pressure, similar to the hand-clamp.
_To Cut a Pile into Strips of Equal Width_
This is sometimes required to be done for a large quant.i.ty of stock and it is desirable to do it with economy of time and labor. The obvious method is to first trim one edge of the stock, then set the back gage to the required width and jog the pile up to it for each cut. This method is usually accurate but requires a great deal of handling of the stock--almost three times as much as is necessary by some other methods.
The following methods require the pile of paper to be first trimmed with a true edge in order to jog it against the back gage, and also with a true edge on the opposite or front side.
1. Make a mark or place a thin paper sticker on the top surface of the front table the exact distance in front of the cutting edge of the knife to correspond with the required width of the strip. Place the pile of paper on the back table with a trimmed edge against the back gage. Move the gage forward so that the front edge of the pile comes to the mark on the front table. Make the cut. Repeat this until the pile is cut up. This requires only one jogging of the pile into place.
2. Same as the method just described, except that a small hinged metal gage is used instead of a mark on the table. This requires a special device. The front f.l.a.n.g.e of this device or gage may be slotted and fastened to the table by a thumbscrew. The vertical angle part must be hinged to the part fixed to the table so that it can be swung upward and back far enough to leave the cut pile room to move forward on the table when the knife pa.s.ses down through the pile.
3. Use a hand automatic s.p.a.cing device, gage screw movement.
4. Use a template placed on top of the pile. Run the clamp down to the pile, place a card or fiber template on top of the pile in front of the clamp. Draw the pile forward until this front edge coincides with the front edge of the template. Make the cut and repeat the operation until the pile is cut up.
5. Draw the front edge of the pile forward to dimension on the regular graduated rule set in the front table.
6. Draw the pile forward the distance desired by reading the steel tape scale overhead, or the dial, or the graduation on the gage movement wheel.
7. Use a hand automatic s.p.a.cing device, chain movement.
_To Cut a Pile Rectangular_