Article goes on to say to check for shear (h).

h=3V/2bd

V=wL/2=931 x 47.25 / 2 = 21,994lbs

h=3 x 21994 / (2 x 12 x 14) = 196psi

Which is way over the recommended value of 125psi for red oak. For EW Pine the Fv value is meant to be less than 65psi. If P. Radiata is comparable then the beam would need to be 23" square giving, h=62.4psi!

Green that sucker is going to way around 500kg!

My conclusions are that either:

- I'm doing something wrong;
- the safety factors, are overly conservative ie there is no need for a continous loading safety factor or wet service safety factor;
- traditonal screw presses, ie pre industrial revolution, didn't develop any where near 20t of force.