Avoid Common Cutting Problems
By: Bruce Peterson, President, Colter & Peterson
A common process like cutting can often be more in-depth than you think. The process of cutting paper is seemingly very straightforward. Material is aligned against either a left or right fixed side guide and a movable back gauge. A clamp holds the pile in place while a knife travels downward, cutting the material. In reality, cutting is a lot more complicated. The failure to recognize and adjust for problems can result in inaccuracies during later processes and in the worst-case scenario, ruining a printing job. The following considerations can save time and money and avoid headaches.
The size must be right
The first step in accurate cutting is to make sure two important factors on the paper cutter are set correctly; the measurement display and the squarness of the back gauge. All paper cutters have some system for displaying the position of the back gauge. Older machines have a ruler while newer machines and updated machines have some type of digital or computerized display. The first step in avoiding cutting problems is to ensure the display shows the correct position of the back gauge. The ability to recalibrate is a feature found on a number of cutters and is a standard part of the setup on retrofit computers. Checking for size is very simple. The back gauge is set to a displayed size and a sheet is cut. The cut sheet is then measured and the actual size is compared to the displayed size. If there is a difference, an adjustment must be made based on each manufacturer’s procedure.
The squareness of a cutter's back gauge (parallel to the knife) is critical for proper cutting. While each manufacturer has a different procedure for adjusting the back gauge a very simple test can be used for checking it. A small narrow pile is cut on both sides of the machine at the same time. The two piles are compared and if there is a difference in the size of the two piles the back gauge is not square. If there is a difference, an adjustment must be made based on each manufacturer’s procedure.
Register (Internal and External)
When cutting printed sheets the factor of register comes into play in two forms; internal and external. Internal register is the position of the images relative to each other. External register is the position of the images relative to the sheet itself. Internal register is the primary concern of the pre-press and press areas. Once sheets are printed they can not be adjusted. External register, while considered for pre-press in layout and on press when printing the sheet, becomes the primary concern of the cutting and finishing departments. While we can not adjust the images for register we can control their relative position in regard to the edges of the sheet. Paper can change size when printed and the decision may need to be made to cut to the image or to cut to size.
It is therefore very important for the cutter operator to receive complete information and a rule out with each job. When setting up the cutter a small lift or even a single sheet should be cut to check that everything works out correctly.
Make sure the knife is sharp
One of the major causes of problems with a paper cutter is the use of a dull or blunt knife. Besides producing inaccurate cuts, the machine will be subject to unnecessary strain.
The signs that a knife is dull or blunt are:
a) A rough or a speckled cutting edge, depending on the material
b) A bang is heard when cutting the bottom sheets of a pile
c) The cut material sticks together
d) The cut edge of the material is ridge like or turned down
e) Inaccuracies in cutting (overcut, undercut, etc.)
Clamp pressure is the critical setting
To obtain maximum productivity on a paper cutter, operators should try to stack piles as high as possible. When stacking material, setting the clamp pressure becomes critical. The basic rule of thumb is to use higher clamping pressure for soft material and lighter pressure for hard material.
A few considerations when starting your next cutting project can mean the difference in a job done right and a costly mess.
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Bruce Peterson is President of Colter & Peterson, the largest independent distributor of paper cutters and paper handling equipment in North America. Employing more than 75 people in four locations, Colter & Peterson specializes in every facet of paper cutter and perfect binding acquisition and ownership, including maintenance and repair, machine sales, safety and productivity upgrades, surplus machines and more. Contact Bruce at (800) 932-0780 x206 or bruce@colterpeterson.com.
