Hi Group
Some weeks ago there was a discussion re the ratio of diameter to length to roof supports.
I have just unearthed a the NCB Training Manual No 2 (Issued in 1950) and I quote :-
' Props may be of wood or steel.Those made of wood are cut from trees of Spruce or Fir and are of circular sectiion.
Experience has shown that as a general rule the diameter of a wood prop should be 1 inch for every foot length of the prop, so that a prop 4 feet long would be 4 inches in diameter, a good wood prop of these dimensions will support a load of approximately 20 tons before breaking. Props of diameter less than 2 1/2 inches are never used even in the thinnest seams.'
Cheers
John
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