I need to calculate the tonnage a medieval wood screw press could generate. In particular I’m speaking of a press used to squeeze water from newly formed sheets paper in-between layers of felt (see picture) however medieval wood screw presses used to extract olive oil or juice from grapes are identical.
I am not an engineer but I will be giving a PechaKucha (a short 6 minute 40 second lecture) to a group of hand papermakers in a few months from now in which I will include the concepts of simple machines like the lever and the inclined plane to gain mechanical advantage.
Such presses exist in museums throughout Europe however being over 500 years old we are unable to use these to test the actual force. Here’s what I already know. The formula for calculating the ideal mechanical advantage on jack screws is straight forward which includes the advantage gained from length of the lever and the pitch of the thread. The much more difficult part is allowing for friction.
I’ve read that even well-lubricated jack screws have efficiencies of only 15% - 20% but that’s for a machined iron screw. The threads on these wooden screws were chiseled by hand with the most difficult part being the inside threads of the nut.
So my question is – is it possible to calculate the efficiency of a hand carved wooden screw? Presumably the upper limit of efficiency would be less than the 15% noted above (and is this 15% figure is correct in the first place)? But what might be the lower end of efficiency be?
Here are the dimensions of the wood screw