H4 



ENGINEERING ON THE FARM 



Mill work. Mill work includes all lumber which has been 

 worked or surfaced on more than two sides, such as window 

 and door frames, outside casings, inside trimmings, base- 

 boards, finished flooring, window sash, storm sash, screen 

 doors, mantels, corner beads, picture rails, plate rails, and 

 any special shapes which may be desired for cornice embellish- 

 ment. 



Curing. Curing of lumber, technically known as drying, 

 has an important bearing on the preservation and life of 

 the structure made from it. The tendency of all lumber 

 is to shrink, warp, and crack as the moisture leaves it 

 (Fig. 1 1 6). These drying defects vary in a greater or less 

 degree with lumber made from different species of trees and 

 in the same species, depending on the age of the tree and 



the part of the trunk from which the 

 piece is taken. 



The defects initiated by drying on 

 coming from the mill are exaggerated 

 by exposure to the air, as the lumber 

 gives off moisture on clear days and 

 absorbs it on damp ones. The effect 

 of drying on some wood is so marked 

 as to render it worthless for the build- 

 ing of permanent structures that 

 would be exposed to ordinary atmos- 

 pheric conditions, owing to twisting, 

 cracking, or its alternate expanding 

 and contracting. The life of a piece 

 of common wood may be extended indefinitely if it is always 

 kept wet or perfectly dry ; but if it is laid on the earth as it 

 comes from the mill and exposed to ordinary atmospheric 

 conditions, it will be rendered worthless in from six to ten 

 years. 



To minimize the deteriorating effects of drying, wood 

 should be as thoroughly seasoned as possible before being 

 u < -d. The best method would be to have the log thoroughly 



Fig. i i 6. Effects of 

 curing 



A — Shrinkage cracks 

 B — Warping 



