What size press you need and features you should seek out depend on your expected customer demands. The most common and popular configurations include four, six, and eight colors over four, six, and eight arms holding the platens.
Standard available features are micro-registration alignment, precision all-heads-down alignment, and tool-less adjustment controls for off contact, pitch, and alignment.
Printers about to buy a new press can get caught up in the thought of how many colors are available to print and forgetting the ability and need to flash while printing. As such, press configuration ends up as a secondary thought far too often.
When a printer is operating a carousel press and needs a flash, there will also be a need for the platen to cool before printing additional colors. At the minimum, this means that a printer will need three platens in operation on the platen arm hub: the print position, the flashing position, and a cooling position.
One of the oddities of the industry is the popularity of the six-color upper hub over the four-platen hub. I have had this conversation with most of the manufacturers in the industry, and they are convinced that the six-hub over three-hub will not sell because consumers do not like odd numbers.
From the buyer’s position, the popularity of the six over four doesn’t justify anything. In the four over four configurations, with an all-heads down press, you have four possible printing positions, or with a flash, two printing positions. When mapping out the printing of a 4/4, there is a load/print, flash, cool, and print/unload available. With the 6/4, there will only ever be two printing positions open. With a flash, the cooling position is in the only available additional print position and has to be unused. This forces the 6/4 into a one-printer station machine with a flash. In use, the printer must rotate the weight of an additional arm and platen and also the cost of an unneeded platen.
With the advent of precision computerized machining, cutting and welding exhaust the manufacturing difficulty reasons for the 6/4 configuration.