Does anyone know the approximate pressure or force of a Kelsey 5x8 press, in pounds per square inch? We are trying to build a platen-style press; although the design will be quite different from a Kelsey, the press area will be similar, but the pressure needed is a sticking point in the design—we don’t know how much it needs. Initially we’ll be using polymer plates but might move to type in the future. I’m happy to report on the end results if it works!
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You are opening an entire world of discussion when you ask “how many psi are required to print?” When I was designing my press, I asked the same question and got a wide variety of answers….. and a lot of debate. Various disciplines within printing seem to have different viewpoints about pressure.
Being an engineer by profession, I tested a few presses with plastic crusher gauges.
Here is what I found out in my little investigation:
A Speedball Lino-Cut press operates at less than 200lbs TOTAL force, or about 8 psi on a 4x6 block…. they do not print very well, though in my opinion. They break at ~10 psi. (240 lbs total pressure)
An 1880’s style Galley Proof Press operates at ~150 to 200psi.
A 5x8 Kelsey broke at ~7500lbs total force. If this force is applied across the entire chase area, it would be 187.5 psi. (BUT you never print a totally solid area on a little press. Generally the rule is to only print with 1/3rd of the chase area “in the black”. This means that each square inch of the actual inked area is operating at a MAX of ~562 psi. )
A Vandercook set up to print a decent page with hard packing seemed to be pressing at about 600 psi. I am fairly sure that it could produce thousands of psi across it’s cylinder’s contact stripe, but one would be foolish to use such pressures for relief priniting.
As a result of my tests, I decided that a pressure range of 150 to 400 psi across the actual inked area is sufficient for letterpress work. I designed my press to operate at a MAX of 300 psi over the entire print area and it prints quite nicely.
Others in the letterpress world will probably disagree with me… and they might be right.
I want to have your babies.
Seriously though, that is just about the most thorough and useful reply I’ve ever received on a discussion board. :) Engineers are awesome. And it makes me feel a little better about trying to build our own press!
I’d be open to hearing other opinions if they do exist, but in the meantime, this will do quite nicely for planning purposes, thank you!
Well thank you! Unfortunately I have to decline….. my wife would not approve, I don’t think. ;)
Before you finalize your design, you might want to look at cylinder presses such as a proof press before deciding upon a platen. Because the cylinder only bears upon a tiny contact stripe at any given moment, instead of the entire surface area of a platen, it is easier to achieve higher pressures. That’s why a 12 x 18 sign press only weighs 100 lbs, where a 12 x 18 C&P platen press weighs a lot more.
Platen presses do have advantages, but they seem harder to build to me.
I posted quite a while ago on press pressures…let me grab from that:
A bit of trivia…a cylinder relief press like a Miehle or KSBA can exert between 200 and 500 PSI. For those working in intaglio, a manually driven etching press can exert upwards of 6000 PSI.
So, Mr. Winking Cat has a point, that a cylinder press might be a better way to go…you can get a lot more pressure out of it, and they can be extremely precise. Some Timken bearings and precision machining is all you need.
If I remember correctly, Harold Berliner (Born 1923, the same year that huge ATF catalog was printed) said of the future of letterpress printing: The two things needed to sustain the printing method were high precision cylinder presses, and matricies for casting.
Neither of those are made any more. Arguably, various plate technologies make casting type a moot point, but eventually the presses will wear out. So, originating and exploring a new press design will be of interest to people down the road.
Anyway, good luck, and keep us updated on your project.
This is the PRESSURE discussion from a year of so ago