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Jan 1, 1996 12:00 AM
What is the correct percentage of paper waste to assign to a job? This question is asked frequently. When it's phrased in this manner, there is no proper answer. Two separate questions are necessary: "How many sheets or cut-offs must be assigned to each make-ready?" and "How many sheets will be wasted during the run?"
The answer to the first question is not expressed as a percentage, but as an absolute number of sheets or cut-offs. The number of required make-ready sheets or cut-offs has nothing to do with run length, but entirely depends on the complexity of make-ready.
Therefore, setup for a folding machine doing two right-angle folds may need 40 sheets, whether it is folding 1,000 or 100,000 pieces. Press make-ready for a two-color job may take 220 sheets, but for a more complex four-color job it could be 700 sheets. Also, on a web press the number of cut-offs for make-ready will vary according to the complexity of the printing and in-line finishing required.
The answer to the question, "What is the running waste?" is expressed as a percentage of the number of sheets, cut-offs or copies being run. Thus, a folder doing two right angles may waste 1.1 percent of the total number of sheets being folded, while a collator-stitcher-trimmer may waste one percent of the run.
On press, the overall percentage of running waste varies according to run length. The longer the job is on press, the smoother things go. Our two-color press may waste as much as 3.7 percent when running 2,500 sheets, and as little as 2.6 percent on a run of more than 25,000 sheets.
Estimators should be equipped with a paper waste allowance chart. For each operation, it would show the number of sheets or cut-offs required for setups and the percentage of running waste as it relates to run length. In computer-assisted estimating, the same kind of lookup table is part of the program's database.
Here is how the table would apply in a specific case. Take 50,000 copies of a 16-page self-cover booklet, 9 x 12-inch page size, four-color, two sided, saddle-wire stitched. It will run sheetwise on a 25 x 38-inch sheet, eight pages to a side.
The calculation should start with the last operation and work toward the first. Estimators should be able to calculate and easily show how many good sheets each workstation must pass to the next operation in order to make count.
Wherever possible, 55,664 (as shown in chart) is the exact number of sheets estimators should assign to the job. Rounding up to an even number of sheets or cartons only increases the estimated cost of the job and tends to make the bid less competitive.
Estimators also should not factor in overs at estimating time. The request for estimate is 50,000 copies. If we used five percent overs in the estimate, the cost would have been for 52,500 copies, which would make the bid less competitive.
Printers wanting to create and sell overs should assign additional paper during order entry. The job jacket would read, "quantity: 50,000 plus five percent overs" and five percent more paper would be assigned. If the shop succeeds in producing overs, customers are billed extra, over and above the quoted price for 50,000 sheets.
The National Association of Printers and Lithographers (NAPL) has published informative booklets and bulletins on waste and spoilage, covering sheet-fed, web and bindery functions. The publications feature tables showing average waste factors of numerous printing firms. They are useful as formats to follow and to get a general idea of the correct numbers.
However, one cannot base estimates on another company's waste factors. To accurately estimate costs, printers should know what is happening in their own shops. To find out, it is necessary to have an effective data collection system. Whether manual or automatic, it must accumulate detailed knowledge of how much paper is wasted on each kind of operation. Then estimators, with or without computer assistance, can predict accurately how much paper will be wasted in the future.
By DON MERIT Contributing editor. Merit is a production management and estimating consultant based in New York City