WORKED BY STEAM. 



687 



in it can be easily removed and another with freshly-sharpened 

 saws substituted. 



The best steam saws have a play of 30 to 50 centimetera 



Fio. 306. 



(12 — 20 inches), giving 200 to 300 cuts a minute. For sawing 

 coniferous woods they have very thin blades with scarcely any 

 set ; they turn out planking, whenever a large quantity of raw 



Via. 307. 



material is available, at rates scarcely dearer than ordinary 

 forest saws. It should also be noted that saw-mill engines are 

 often driven by burning sawdust and refuse wood instead of 

 coal, this being rendered possible by the use of special furnaces. 

 Besides fixed saw-mills, portable frame-saws, termed in 

 America pony-saws, are now employed. Fig. 307 shows their 



