Estimating Folding Time
Q: We seem to make a lot of mistakes in estimating folding time in our in-house bindery. How do the pros do it?
A: Folding rates are a function of the speed the manufacturer built into the machine, the characteristics of the paper being run, and the degree of difficulty of the folds.
If your folder's rated speed is 7,000 inches per minute, and the sheet you are folding is 11" long, add 10% to the length for the sheet gap, and the following formula gives you the number of sheets you can fold per hour:
7,000" ÷ (11" + 1.1") = 578 sheets per min. or 34,680 per hr.
That's if the stock can take the stress of running that fast; usually newsprint, recycled paper, and light weight stock cannot; neither can coated or heavy stock. Factors such as curl and static will also slow down production.
If your 8 1/2" x 11" sheet is to be folded in thirds to a #10, the job lends itself to being run 2-up on a 17" x 11" sheet, thus doubling your output to almost 70,000 finished pieces per hour. At this speed manning would probably be one loader and two catchers.
But we figure the maximum speed of parallel work on a 7,000" per minute folder is 5,500" per minute.
And for right angle work, real-world speed is 3,500" to 4,000" per minute. So if you have a 16-page signature on a 23" x 25" sheet of 60 lb. paper, you should figure on running 4,000" per minute, giving you this calculation of output speed:
4,000" ÷ (35 3.5") x 60 = 6,233 sheets per hour. We have occasionally run 16s at 11,000 per hour, but not often.
Other factors that can slow you down are imposition, slitting and chasing, split guides, map folds, gatefolds, trimming waste while running, gluing, etc. Make-ready times are significant, too-and hard to predict.
With the host of factors that can degrade folding speed, it's only our operators' years of experience that guides them in estimating how much speed will be lost for each of these factors.
Finally, keep this in mind: today's new machines are way ahead of machines manufactured 5 or more years ago. The older your equipment, the tougher it is to schedule reliably. We've ordered two new folders-one for signatures and one for maps-to stay on top of the technology.