FOREST UTILIZATION 79 



Lumber can be more evenly dried by steam than by hot 

 air. 



Sapwater heated to boiling point expands 600 times. Con- 

 sequently, wood at 212° F. contains only 1/600 of the 

 water originally found therein. 



Before building a mill be sure to consult insurance com- 

 panies, submitting mill plans. 



The insurance company prescribes the distance between 

 the yard, boiler house, engine house, mill and dry kiln. 

 The rate of insurance on a mill is 5% and over. 



§ XVIII. WOODWORKING PLANT. 



A. Planing (surfacing, dressing or sizing). 



The planer consists of cylindrical cutter heads carrying two 

 to four knives and making 3,000 to S,ooo revolutions per min- 

 ute. It is preferably belted at both sides. 



The smaller the diameter of the cylinder with its knives, the 

 smoother is the planing. 



The feeding is done either by two to four feed rolls (above) and 

 friction rolls (below) or by a traveling bed. The entire 

 cutting length of the knives should be uniformly used. 



The top cutter should do the heavier work in double surfacers. 



The knives are usually sharpened automatically. 



Lumber is fed into the machine at the rate of 20 feet to 150 feet 

 per minute. Hardwoods more slowly than the soft woods. 



The chip breaker is merely] a front pressure bar preventing long 

 splinters from being torn oflf. 



Price of single planers is $100 to $400; of double planers $400 

 to $800. 



No machine should have wood in its construction. 



B. Flooring. 



The flooring machine is a surfacer having an additional outfit 

 of I two side cutters revolving on ratchet spindles, cutting 

 tongues and grooves. 



The machines weigh s tons and more. 



The usual flooring made is hard maple. 



Planers and flooring machines must be provided with a folding 

 hood connected with an exhaust fan, so as to prevent the shav- 

 ings from clogging up the machinery or from pressing them- 

 selves into the planed surface, 



C. Resawing. 



Resaws are either circular or band resaws. 



The use of a resaw involves a great saving, since it takes a very 

 fine kerf and at the same time relieves the work of the main 

 saw. 



The feed is automatic and consists of four rolls. 



Circular resaws have as low' as 19 gauge at the rim and are fre- 

 quently built as segment saws. 



