Saturday, September 20, 2008

Wheels Within Wheels

There's been a lot of discussion on Briar Press and the LETPRESS mailing list recently about operating a press safely. One of the important factors to consider is the speed of the press. Without a treadle or variable speed motor, running the press at a slow enough speed for safe operation, whether for a beginner or experienced pressman, is not always so straightforward.

To use my press for an example: It came from a print shop where the printer had over 50 years experience. The press had a 1725 rpm motor which gave 36 impressions per minute when belted to the 24" pulley on the drive shaft. Needless to say, this was much too fast for me and probably even for many experienced printers.

The press had no treadle and an expensive variable speed motor was financially put of the question. The answer was to slow the speed down by the use of an intermediate pulley arrangement known as a countershaft. By adjusting the diameter of the pulleys in this setup the speed of the press is adjusted up or down. In this case, the pulley on the motor is a 2" V-belt pulley which is belted to a 6" V-belt pulley on the countershaft. On the end of the shaft is a 2" flat belt pulley which in turn is belted to a 24" flat belt pulley on the press. The motor, 2" and 24" flat belt pulleys came with the press.

The photo below shows my countershaft. I was fortunate in having an old motor mount with a built-in countershaft but a similar setup could easily be made out of wood and with pillow blocks, a shaft, and pulleys purchased from an industrial supplier, flea market, etc. The wide pulley under the belt is an idler pulley to keep tension on the belt and help it wrap around the small pulley better and provide more surface contact. This is not essential but I had it laying in my basement and it works well. I made the base for it out of wood, the same as can be done for the main countershaft and motor mount.

I've read and been told that 14 impressions per minute is a good speed to start for a beginner, or even slower. My press runs at 15 ipm and as a beginner I'm very comfortable with that speed. I thought I would post this to show a less common but effective, inexpensive, and relatively simple option to run the press at a safe speed.

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