iron hand press pressure

Greetings! Does anyone have a number, specific or just an estimate, at to the pressure generated when printing with an iron hand press? (The amount of pressure that the platen exerts on the paper/type when the bar is pulled. My press is a R. Hoe No. 4 with a platen size of approximately 22 x 30). Out at the Printer”s Fair in Mt. Pleasant, Iowa they have a big Wessel that generates some incredible amount of pressure but I cannot remember the number listed on the signage. As an aside, if you get a chance to visit the Printer’s Fair at their annual event in September go for it! Thanks all for your time and thoughts on this.

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I can’t give you a number but I can say that with a forme well filled with type, almost to the edges, I need to plant my foot and use both arms and a swift movement to draw the platen down. My press is an Ostrander Seymour Washington with a platen of around 18 by 22 inches (not nearby to measure at the moment).
When the forme has little type you may not feel any resistance from the impression at all.

As you can guess the pressure number varies with model and maker. The impression mechanism consists of a train of levers. I calculate it by figuring out the mechanical advantage of each of the levers: the bar typically has a mechanical advantage of about 6-8:1; the upper toggle joint has a similar mechanical advantage range depending on the model; and as the upper joint closes it straightens out a sort of “knee” joint, and in straightening that the mechanical advantage increases almost exponentially. The key is that the distance moved by the printer’s hand pulling the bar and the resulting platen movement downward make a changing ratio, increasing as you arrive at actual impression, with the toggle closed, almost to infinity. If you had a compression micrometer you could place between the platen and bed and compare its reading with a measurement of the distance moved by the hand on the bar and the force applied to the bar by the hand multiplied by that ratio will tell you the force applied to the platen at its center. Then you have to calculate the total contact area of the printing surface (if it’s type, the area of the face of each individual letter, totaled) and divide the applied force by the surface area to get force per unit area. Knowing just the platen surface area and the force doesn’t give you the true picture because with text type the ink area is only about 10% of the area of the foot of the letter , or less and its the area in contact with the paper that determines the pressure there. Sorry! Long explanations are my specialty!


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