084 SAW-MILLS 



ever, which depends on the best mechanism, ns a rule, the large 

 mills are superior, owing to their smooth cut. 



Section III. — Steam Saw-mills.* 

 1. Frame-sairs. 



Although most of the saw-mills which will be now described are 

 driven by steam, the use of water-power is not excluded ; it must 

 then be strong and steady so as to be suitable for powerful turbines. 

 "Whilst forest saw-mills usually work with only one saw, or at 

 most two saws, steam saw-mills are supplied with a number of 

 saws and other wood-working machines, so that they can turn- 

 out wood completely ready for use in buildings, &c. They differ 

 chiefly from forest saw-mills by their enormous outturn and its 

 better quality. 



Besides differing from forest saw-mills in these points and in 

 their motive power, steam saw-mills are also constructed differ- 

 ently ; being completely formed of iron they are more compact, 

 stronger, possess greater stability and work more evenly ; 

 friction is reduced to a minimum and they are much more 

 powerful. This greater power is specially utilised in steam 

 saw-mills by there being several saws, up to 10, in the same 

 frame, all of Avhicli work at once ; a butt is thus sawn into 

 planks in one operation. These arc termed multiple saws. 

 As regards the power required to drive multiple saws, it is 

 estimated that 3 horse-power is required for the empty frame 

 alone, one horse-power for the first four blades and for every 

 other blade half a horse-power. These saws are constructed 

 on the same principle as ordinary saws, but mechanical improve- 

 ments are introduced to increase their efficiency and reduce the 

 motive power required to drive them. 



Figs. 'dO'i and 305 represent one of the numerous kinds of 

 multiple saws from the catalogue of Kirchner & Co. of Leipzig. 

 The frame, which is generally driven from below (A), runs very 

 smoothly in simple bearings (a a) and may support 10 to 20 

 blades at suitable distances. The blades are usually fixed in 



* An excellent account is given of modern American saw-mills by Hotchkiss, in 

 ?',ucyc. Brit., 1880, vol. xxi. Also see Worssani & Co.'s catalogue (King's. 

 Koad, Chelsea). 



