POWER WOOD-WORKING MACHINES 437 



slip off. The slipping off of a counterbalance, due to a set 

 screw working loose, recently cost a workman his right hand. 



The dangers incident to the use of circular saws are too 

 well known to require description. A "riving knife," or 

 "spreader," when properly attached to the table immediately 

 back of the saw, will spread the cut sufficiently to prevent 

 cramping. It is very important that cramping shall not 

 take place, as this usually stops the saw and throws the belt 

 off, or throws the work back on the operator, often with 

 serious results. 



The riving knife is simply a piece of sheet steel mounted 

 in a vertical position back of the saw and preferably curved 

 to conform somewhat to its outline. The edge near the saw 

 should be a little thinner than the saw itself, so that the 

 saw cut will slide over it easily. The opposite edge should 

 be at least the thickness of the saw, or even of a slightly 

 greater thickness. The length of the knife will, of course, 

 depend upon the size of the saw with which it is used. 



Another very simple device to prevent the work being 

 thrown back in case of cramping, consists of a board 4 or 5 

 in. in width, fastened perpendicularly to the ceiling directly 

 over the saw, and of such length that its lower end will just 

 clear the saw. The plane of the board should be at right 

 angles to that of the saw. 



If a saw without a guard is permitted to run while the 

 operator is away, a small oblong wooden box placed over it 

 will serve as a safeguard to persons passing the table. If 

 practicable, this box or cover should have, in each end, a 

 dowel pin fitted in the table. 



505. Jointer Guards. The hand-planer or jointer is a 

 most dangerous machine when operated without a guard. 



