Speed

In the US, speed is measured in 8.5x11-inch sheets per minute - simplex. But most printing is duplex. In most cases, if you halve the simplex speed you get the duplex speed. If you can print both sides of the sheet more or less simultaneously, you can increase the duplex speed. On sheetfed printers, both approaches exist for monochrome printing, but not for colour.

Since digital colour came to market in 1993, speeds have been creeping up. You can buy sheetfed digital colour printers at almost any speed point: 20, 35, 40, 50, 55, 60, 65, 70, 80, 90, 100, and 110. The 20-40ppm printers are bargains today and one can start low and then add new machines with higher speeds. There are more models at 70ppm than any other. Within a year, 100ppm could be the benchmark. You need the high simplex speed to deal with the duplex volumes. Thus, a 100ppm printer is really a 50ppm printer when you realise that 70% of all printing is duplex.

Sheet size

8.5x11 [roughly A4] and 11x17 [roughly A3] were US standards because digital printers evolved from copiers. In other parts of the world, metric rules. The US quickly moved to 12x18 so there could be bleed and after 2005, the 13x19 [between A3 and B3] became the new 12x18. Most printers have a fraction, such as 13x19.2 and I have left the fraction out in this discussion. When I look at paper purchasing for digital printers, the most common size is 11x17. Older model HP Indigos run 12x18 and 13x19 for newer models. But all other sheetfed printers can handle 8.5x11, 11x17, 12x18, and 13x19, and custom sizes. The Kodak Nexpress applies a lot of Heidelberg thinking and its size matches the GTO press at 14x20 (B3+). The Xerox iGen series in 14x22. Some Xerox models are 12.8x19.2.

I feel for the paper suppliers who must maintain SKUs for all sizes for all printers. In a few years, many toner-based printers will max out at 14x20 or so. This size is especially relevant for larger format book covers with bleed.

Resolution

Remember when 300dpi was good enough? We have now evolved from 600dpi to 1,200dpi to 2,400dpi. I think 1,200dpi was great, especially if there was a higher bit depth. But it appears that new laser systems will provide a modus operandi to reach 2,400 dpi.

But I use the numbers as a guide and emphasize a review of actual output. A 1,200dpi printer may in fact produce better quality than a 2,400dpi printer.

Monthly volume

There are as many printers at 100,000 impressions per month with slower printers as there are at 1,000,000 impressions per month with high-speed printers. Almost all have a click-charge basis for use. Duty cycle is the theoretical average number of pages the machine should print in a given time period, generally one month. Exceeding the duty cycle on a regular basis can lead to malfunctions and breakdowns over time. Alternatively, not printing in numbers close to the duty cycle could mean additional charges. There is also a monthly volume that you have contracted for. If your volume is over that contracted number, you may pay an additional charge for each impression. 

Paper 

Most sheetfed digital printers can handle a maximum of 300gsm with a few at 350gsm. 70gsm tends to be the minimum, although a few can handle lighter weights. Roll-fed printers can handle even lighter weights. 

Frank Romano is professor emeritus at the Rochester Institute of Technology. This article first appeared in ProPrint.