SAWING MACHINERY. 



549 



when the spaces are thus filled up, they are kept tight 

 .Machinery, by screws tapped in the sides of the saw-frames. Each 

 ^^"Y"*"*' saw is strained in succession by a steel-yard, construct- 

 ed as follows. A strong axis goes across the fixed 

 frame in which the saw-frame slides ; and above the 

 top of this frame from one side of this axis proceeds a 

 lever, which has a weight fixed at the end, and from 

 the opposite side of the axis proceed two short levers, 

 which are connected by links with a strong cross bar, 

 situated immediately above the upper cross bar of the 

 saw-frame, when it has reached its highest elevation. 

 Upon the steelyard cross bar is a shackle or link, 

 which can be united by a key with any of the shac- 

 kles on the upper cross bar of the frame, which shac- 

 kles, as we have already said, are united by their hooks 

 with the upper end of their corresponding saws. By 

 this means the lever with its weight becomes a steel- 

 yard, by which any one of the saws may be drawn 

 up with a given force. 



In order to apply the steelyard, the frame is raised 

 to its greatest height, and wedges are then put in be- 

 tween the top of the saw-frame and a fixed part of 

 the stationary frame, so that the saw-frame may be 

 kept fast when the steelyard is applied. The sharp 

 saws are now put into the saw-frame by hooking them 

 on the lower cross bar, and uniting the upper hooks 

 to the shackles on the upper cross bar. The pieces of 

 wood are then introduced between the saws, accord- 

 ing to the size of the wood, and they are bound 

 fast by screws. The loaded end of the steelyard 

 is now lifted up by a rope going over a pulley, 

 so as to allow the link in the cross bar of the steel- 

 yard to be united with the shackle of one of its 

 saws by its keys. The steelyard being now allowed 

 to descend, it stretches the saw with a force depend- 

 ing upon its load. The wedge of the shackle for the 

 saw is then thrust in by the hand as far as possible, so 

 aa to retain the saw at the tension given to it by the 

 steelyard. The shackle of the steelyard is then dis- 

 engaged from the saw and removed to the next, which 

 is stretched in a similar manner. 



In this saw mill, there is a contrivance by which 

 each saw frame is allowed to retreat a small quantity 

 in its ascent, in order that the teeth of the saws may 

 keep quite clear of the wood when they ascend and do 

 not cur. 



Circular saws, or saws of a circular form, which cut 

 during a continuous rotatory motion, have been used 

 for cutting the teeth of watch and clock wheels since 

 the time of Dr. Hook. They have been long used in 

 Holland for cutting veneers, and they are said to have 

 been introduced into this country by General Bentham. 

 Mr. Taylor of Southampton, and Mr. George Smart, 

 had the merit of introducing them very early ; but we 

 do not know the exact dates. 



A circular saw is nothing more than a circular plate 

 of steel, having teeth upon its circumference, and 

 made to revolve upon an axis with great rapidity, by 

 means of bands or straps. The saw itself may move 

 either on a horizontal, a vertical, or an inclined plane ; 

 and as the timber may be laid upon a plane inclined 

 in any given direction, it may be sawn in lines mak- 

 ing any angle whatever, or at any given distance from 

 one another. When the saw is fixed at a certain angle 

 and at a given distance from the edge of the frame, 

 all the pieces of wood may be cut exactly of the same 

 size, by pressing them against the edge as the saw is 

 cutting them. The following is a description of the 

 circular saws at Rothiemurchus in Inverness-shire. 



There are two kinds of saws made use of in the 

 Rothiemurchus saw-mill, circular saws and upright 



Circular 



Cirrul** 



ones. A circular saw is a thin round plate of teel, 

 toothed on the circumference fixed on a revolving axle. Mcfctor)r. 

 An upright saw is the common paw made use of by 

 awyers, fixed in a frame moving vertically. In both 

 cases, the log to be *awn is fixed to a frame, which i 

 moved against the saw. Each of thete comt ruction* 

 has peculiar advantages. The upright aw, it it evi. 

 dent, cuts only in descending ; there are aUo two 

 poiius in every ttroke at which it is stationary , the 

 one when it is at its height, the other when at it* 

 lov.est. A large proportion of the time of each stroke 

 is thus consumed without effect A circular taw cuts 

 during the whole of iu revolution ; and it is found 

 that a much greater velocity can be given to a circu- 

 lar motion, which is equal and constant, than to an up- 

 right one, which is necessarily unequal. A circular 

 saw is thus much more expeditious than an upright 

 one. It is, however, much more limited in its appli- 

 cation, as it can only work in wood of less depth than 

 the radius of the saw. The size of wood is further 

 controlled by the thick plates of metal which are made 

 use of to fix the saw on its axle. These Jlaungct, as 

 they are called, it is found by experience, require to 

 be about one-third of the diameter of the saw. Be- 

 sides this, the size of the saw itself is controlled by 

 the thickness required to give the plate sufficient stiff- 

 ness. A circular saw, too, one-eighth of an inch thick, 

 would occasion much lo;s in saw draft. In this mill no 

 saws have ever been used above three feet diameter. 



The application of upright saws is controlled only 

 by the length of stroke given to the saw frame and 

 its size ; the stiffness of the saws is given by stretch- 

 ing them tightly between the upper and lower end* 

 of the frame, and is therefore in a great degree inde- 

 pendent of the actual size of the saw. 



The intention in this mill is to saw by circular saws, 

 where they would not occasion too great a loss in saw 

 draft ; and in this case only, to saw by upright ones. 



The circular saws run about 1000 turns per minute, 

 and will cut 10 inches deep on 3-l(hhs of an inch of 

 saw draft. The upright saws make about 120 strokes 

 per minute, and will run on rat fieriest saw draft. 



The circular saws will cut a 12 foot log in less than 

 a minute ; the upright saws in equally fine work, 

 will not cut above 15 inches in the same time. 



In the process of making deals with circular saws, the 

 first operation is called stabbing ; it is to reduce the 

 tapering round log into a plank as thick as the deals are 

 intended to be broad. This is done by running two 

 saw-drafts parallel to each otber through the log, which 

 products a flat-sided round- edged piece of timber ot 

 equal thickness, but tapering in breadth. The slabbed 

 log is then cut into deals ot the required thickness, by 

 running the saw through it as often as is necessary at 

 right angles to the former saw drafts. 



In chis mill the slabbing is performed by two saws 

 fixed on the same axle, S, S, Figs. 2. and 3. the dis- 

 tance between which regulates the thickness of the 

 slabbed log. A plank or batten B, so narrow as to 

 pass freely between the saws when at the least requir- 

 ed distance from one another, is laid parallel to the 

 face of the saws in the centre between them. A 

 broader plank D, E, is laid parallel to this batten on 

 the outward side of each saw, as far apart as to pass 

 the saws freely when at the greatest required distance 

 from one another. These three planks are connected 

 together by cross pieces A, C, at the ends, and be- 

 ing laid on rollers R parallel to the axle of the saw, 

 form a table, moveable backwards and forwards, 

 limited in either range by the connecting cross-pieces 

 coming against the saws. This travelling table is 



PLATK 



-XXII. 



Figs. 2 and 3. 



