By R.O. Vandercook, Printing Equipment Engineer, October 1935
Dear Editor: I was very much interested in Mr. Carty’s discussion of the subject of register varying with the speed of the printing press cylinder.
Discussion of the subject a long time ago caused me to make some investigation on my own account. I had always noted that it was better to run color register jobs at the same speed, but I did not stop to consider the reason why.
By watching the gripper action closely on my own cylinder presses I came to this conclusion: The grippers were closed by the action of a spring. The grippers, therefore, closed at a constant speed that had nothing to do with the rim speed of the cylinder. If the cylinder was going continuously at a rim speed of about a thousand impressions an hour the grippers closed down on the sheet and therefore the sheet went through in register, but upon increasing the rim speed of the cylinder to produce 2000 impressions per hour the sheets which had been run at 1000 per hour would not register with those run at 2000 per hour. Why? I found it all in the gripper action. Doubling the rim speed of the cylinder while the grippers were closed by spring pressure at a constant speed caused the grippers to close down on the sheet a little later in relation to the travel of the cylinder than they would at a lesser speed, therefore the sheet went around the cylinder in a little different position at higher speeds than at lower speeds. Speed- ing up the dropping of the grippers by putting in livelier springs and lessening the distance of the drop while under spring tension helped some, but the common sense way out of the difficulty was to run color register jobs at practically the same speed.