Saw mills their arrangement and management

On the publication of the Author's book, "Wood-working Machinery: Its Rise, Progress, and Construction," it obtained a large measure of success. Finding, however, that a more comprehensive and detailed description of the arrangement and management of saw-mills, railway wagon and other wood works, would have rendered it of more service to those absolutely engaged in wood conversion, the Author determined, as his leisure permitted, to write an additional hand-book as a companion to the first; and the present work is the result. The Author has endeavoured to make his descriptions as simple as possible. He has printed a number of rules connected with the subject, but has abstained from inserting intricate theoretical calculations which, even when found in books designed especially for the use of engineers, are not always worked out by their readers, and may or may not be in accord with absolute practice. Tables of speeds and rates of feeds for various machines will be found, but the Author desires it to be distinctly understood that the figures given are not intended to be absolute, but as bases on which to work, and to be modified as circumstances or the special nature of the work may dictate. As the principles, nature of material, and circumstances involved in the operation of wood conversion by machinery are so many and so varied, to lay down an arbitrary table of speeds would practically speaking be impossible.

As competition in the conversion of timber has increased year by year, to secure an adequate return on invested capital it has become necessary to arrange and work saw-mills and wood converting works on an improved or, we may say, a more scientific basis than has hitherto been the practice; and, with this end in view, the Author has re-modelled and arranged a number of old mills, with very satisfactory results, both as regards output and working expenses.

In commencing this Book the author thinks it well to say he has no startling new plans or theories to propound, but simply intends to give briefly some of the practical results deduced from a lengthened experience in the construction and management of wood-working machinery.

A saw-mill being for the purpose of converting crude material into articles of commerce, the chief point to be aimed at is how to accomplish this with the greatest economy and despatch combined with quality of production.

As regards the arrangement of the saw-mill, some difference of opinion exists as to the best form, and as in crowded cities all kinds of buildings have to do duty, no arbitrary plan for setting out a mill can be laid down, for it necessarily varies according to the requirements or circumstances of the case. It must be admitted, however, that as a rule sufficient attention is not given to this very important point, the result being a daily loss in working through badly-arranged machinery: this loss in a day may appear small, but in the course of a year amounts to a very considerable sum, and is one that should not occur.

Again, the size and shape of a mill should be varied according to the nature of the work to be carried on; for instance, a mill adapted for green timber or general timber conversion would be unsuitable for a business chiefly consisting of floor board planing, &c., or for a railway carriage and waggon works. We will, in the first instance, briefly consider the requirements of a general saw-mill, where sawing, planing, moulding, and most kinds of wood conversion are carried on. Assuming ample ground space to be obtainable, we have found a rectangular building of a length of about two and a half times its width the most suitable shape. The building should be arranged with large sliding doors at either end of the mill, so that timber may be passed in at one end in the rough, and, after being worked through the various machines, passed out at the other as manufactured goods. A tramway should run down the centre of the mill, and where much heavy timber is worked an overhead traveller is necessary. In arranging a mill, advantage should always be taken of the site with reference to land or water carriage of the timber, as much money is often spent in unnecessarily hauling it about. If near a canal or river, the building should be so planned that as the timber leaves the water it shall pass directly to the heavy machines, such as the cross-cutting machine, timber
frames, or rack benches for breaking down; its further manipulation is thus at once made easier.

It will be seen from the plan that the boilers are placed in a house entirely separated from the mill. We shall give elsewhere a sketch of an improved plan for fixing them that has been found very satisfactory in practice. The engine also is separated from the other machines. Sheds for storing sawn timber are not shown in the plan, but we strongly recommend their use in preference to outdoor storing, as the wood is thus saved from unnecessary deterioration from the action of rain, frost, or sun. In designing these sheds care should be taken that the air is allowed to circulate freely through them.

The cross-cutting machine marked No. 8 on plan is placed below the mill floor, but is arranged so that it may be raised above or depressed below the floor line at pleasure, so that if a heavy log is brought into the mill and placed over the machine it can be immediately cross-cut and made at once more portable for future manipulation* The rack circular saw bench and log frame are so arranged that logs can either be rolled from the timber truck or dropped by the overhead traveller into position for sawing. The circular saw bench (No. 8) is arranged with a roller and rope feed. This combination is especially useful, as the continuous roller feed is capitally adapted for sawing deals, but is useless for round timber, for sawing which the rope feed comes in. No. 14 on plan is a small saw bench arranged with two saws, one for ripping and the other for cross- cutting. These saws are mounted on separate spindles, arranged to run in a revolving frame, which may be worked by a hand wheel and worm gearing, and either the rip or cross-cut saw be brought into use above the table, as may be desired, the saw not required sinking at the same time below the level of the table. This bench is especially useful where there are frequent changes in the nature of the work.

Occasionally it will be found advantageous to fix the log frame in a small building outside the main one, as in many cases the gantry crane cannot pass right through the saw-mill It sometimes also happens that from water or other causes it is impossible to dig a deep enough foundation for a large log frame; in this case it is necessary, to overcome the vibration in working, that the base plate be much extended, and that the machine itself be entirely self-contained. Should the log frame be fitted up outside the main building, and no belt power be readily obtainable, it can be driven by a separate engine or a cylinder attached directly to the top of the frame.

If the cylinder is attached to the top of the frame, the crank shaft is usually carried in a framing below the cylinder, and has a pair of fly-wheels fitted to it, one on each end; from these, connecting rods are attached to the swing or saw frame, and a cross-head fitted to the top of the piston rod; thus motion is given to the crank shaft and swing frame. This plan is also very useful where there is ample boiler but lack of engine power. Where no difficulties of site, &c., arise, however, we prefer the ordinary form of log or timber frame, driven by belts from below.

A combined thicknessing and surface-planing machine, with hand and power feed, could be added with advantage to the plant we have sketched in plan, or any other machines adapted to any special kind of wood manufacture it is desired to carry out.

A covered shed, or sheds, for the reception of dressed timber, should be attached to the mill, and also a magazine for shavings and sawdust made near the boiler- house. This and the engine-room should be made as nearly fireproof as possible, with iron doors to separate them from the mill. The chimney-stack base is best made of stone laid in cement, and the boiler-room floors also should be cemented,

All saw-mill floors, whether ground or otherwise, should be made of ample strength to withstand machine vibration or any load that may be placed on them. The ground floor should be built on piers or columns, and a cellar made for chips and sawdust. We have found joist floors the best form of flooring to use, as from their construction they resist successfully any excessive vibration. Where a single floor is used, and the bearing exceeds 10 ft., herring-bone strutting should be employed. It is very important that all machines should be perfectly steady in working, especially those with high-speeded revolving cutters, such as moulding machines, or the work turned out will be marked or jarred, and in the case of very thin mouldings the wood has a much greater tendency to split.