The one-piece back gage was improved by cutting it into two or three sections so that the first and final cuts of two or three piles may be made at every stroke of the knife. Adjusting screws are provided for tilting the back gage forward or backward to compensate for the variation in the width of the top and the bottom sheets which occurs in the same machine and with the same knife when cutting hard or soft papers. A swinging adjustment is also provided to "square" the back gage parallel with the knife edge.
Various devices for taking up the slack caused by wear in the table slot guiding the back gage are furnished, but probably the simplest and best method is the replacement and refitting of the inexpensive sliding part.
INDICATOR ATTACHMENT FOR BACK GAGE
The distance the back gage is moved is read in different ways. The movement of a gage operated by a screw and wheel is indicated by a pointer on the front edge of the table overlapping the rim of the long screw wheel. If the rim of the screw wheel is lined off in sixteenths of its circumference, the pitch of the screw being one inch, each complete turn of the screw wheel means that the back gage is advanced one inch, and each one-sixteenth turn means that it is advanced one-sixteenth of an inch. It is important always to keep turning the screw and wheel the same way when so measuring, because otherwise the "back lash" (looseness of the screw and its nut to permit easy working) will cause variation.
For a back gage moved by a chain or a wire cable or a metal tape, a graduated dial is attached to the top of the cable hand wheel which reads from a pointer attached to the front edge of the table.
Both these ways of reading require the operator to look down.
For a back gage moved by power, a steel indicator ribbon passing around a wheel overhead in the frame cap and attached to a standard on top of the back gage (see Fig. 7) enables the operator to read the position of the back gage without looking down, and a second wheel indicator and pointer permits reading to less than one-thousandth of an inch. Similar indicator ribbons are attachable to the back gage for screw, cable, chain, and metal tape movements.
These indicator ribbons are usually graduated and marked for inches, halves, quarters, eighths, and sixteenths. They are also furnished with metric system measurements, graduated and marked for centimeters and millimeters. They are also furnished extra wide so that both the English inch measurements as well as the metric system measurements may be put upon the same ribbon. When graduated to thirty-seconds of an inch and millimeters a good magnifying glass of about three inches diameter, adjusted in front of the pointer, enables easier and more accurate reading. An easily operated lock for holding the back gage fast to the table at any exact mark prevents variation in the width of cutting.
Fixed distance gage rods and suitable engagements with the back gage are provided for cutting at any time duplicates of exactly the same width, especially valuable for loose-leaf ledger work. Pins and holes drilled in the back gage and table also secure uniform locations impossible to get solely from reading the overhead ribbon or an indicator dial, which latter may be read incorrectly because of poor light or variation in the operator's position or eye.
Locking devices for the back gage ordinarily consist of (a) a friction grip around the moving screw, or (b) about the cable hand wheel, or (c) a clamping device which holds the back gage, or (d), best of all, a fixed grip rod-holding device operated from the front of the table, thus eliminating any possible lost motion through connecting parts from the jogging or chucking of work.