American Printer's mission is to be the most reliable and authoritative source of information on integrating tomorrow's technology with today's management.
Jul 1, 1996 12:00 AM
If there weren't so many differences between jobs, calculating press time would be a snap. Depending on the number of colors, we would just allow a fixed amount of time for wash-up and makeready. When it comes to running, once we figured out the number of sheets, we would know how many impressions. If the job prints one side, it's the same quantity. If it prints two sides, we would double the figure. Then all we would have to do is divide by the number of impressions the press yields in one hour.
However, there are many differences from one job to another. Make ready is affected by much more than just the number of colors. How close is the register? How heavy is the coverage? How critical is the color match? Will the customer be there for the press okay? How fussy is the client? Will buyers be knowledgeable and decisive or will they vacillate back and forth?
When installing computer-assisted estimating programs, the systems want to be told how long it takes, on the average, to do a makeready for the first color and then for each additional color. It is up to estimators to know enough about each job to apply a proper difficulty factor. Estimators do not have to remember the average length of time. They simply judge how much easier or harder than normal it is. On many systems, if it is 20 percent harder, they simply type in 120 and the computer does the rest.
Estimating programs also want to know how long repetitive makereadies take. The first form takes care of coming up to color and setting the press for paper size and weight.
On work-and-turn jobs, there must be a time allowance for changing the side guide. The same goes for drying time when a work-and-turn job is a short run. The amount of dry time varies with the length of run and type of paper.
When calculating wash-up time, most printers begin with the premise that there is always black ink in the black ink fountain. They allow so much time for the first non-black color and somewhat less time for each additional color. They usually allow a set time for all four cylinders for four-color process. Again, with wash-ups, it is necessary for estimators to apply a difficulty factor because it takes longer to wash a light color than a dark one.
The more sophisticated computer-assisted estimating programs can be very accurate when calculating running time. They do much more than work from just an average number of impressions per hour. Using data from installation day, these programs allow for differences in quantity, paper thickness and ink coverage.
The accompanying chart shows how an estimate would appear. The lengths of time used are feasible, but they should not be applied to any specific plant.
The specs: 10,000 copies, 16 pages self-cover, 8 1/2 x 11 inches, no bleeds, printed black and one Pantone color on 60-lb. uncoated offset, saddlestitched. The register is close and ink coverage is 40 percent. There is no customer press okay. We are running it as two eights streetwise on a 23 x 35-inch sheet. The paper calculation has been done, allowing 300 sheets for bindery waste, 500 for makereadies and 500 for running waste, making a total of 11,300 sheets.
There are only 21,600 impressions because it is not wholly accurate to take the entire 11,300 sheets and multiply by two. Putting ink onto the 500 makeready sheets was charged for as part of makeready.
The total time is 340 minutes divided by 60 = 5.67 hours, which would be multiplied by the press' hourly rate.
With certain differences, the same methods apply to web press work. Most web presses print both sides of the sheet in one pass. Therefore, there is no such thing as work-and-turn or dry time. In our example, there would be no repetitive makeready. It would be just one two-sided makeready, but on a 32 pager, the second makeready would be repetitive and take far less time.
Similar to sheet-fed, once we know the number of cutoffs, including waste, we know how many impressions are required. It would make no difference whether jobs print one side or two.