Wood-working factories and machinery

In the 'Treatise on the Construction and Operation of Wood-working Machines,' it was necessary to introduce a large number of expensive engravings, and to treat of many things not directly connected with the processes of wood conversion, but relating entirely to the construction of machines. This, while it added to the value of the work for engineers and machinists, at the same time extended its cost, and placed it c beyond the means of machine operators and wood mechanics generally; besides, the plan of the work did not include the practical details of shop manipulation.

In view of this fact, and further to promote the development of wood manufacture, it has been considered expedient to supplement the ‘Treatise on the Construction and Operation of Wood-working Machines,’ with a shorter one, directed to their care and management, including the plans of arranging and equipping factories for wood work, and particularly the details with which the practical workman has to deal.

The work is mainly based upon American practice, which can hardly detract from its usefulness in other countries. The wood interest is more extended in America than elsewhere, and we have every reason to assume, that with our present facilities of intercourse, wood conversion, like other manufacturing processes, will become analogous and uniform, as it progresses and improves.

It was intended to confine this treatise as much as possible to practical shop matters, and not to include the principles of machine construction or of machine action; but it is evident that a mechanic qualified to take care of, to set, arrange, and adjust, or to devise ways and means of working with cutters, should proceed upon general principles and understand the theory of their action. Therefore the following brief article on the subject, from the writer's  Treatise on the Construction and Operation of Wood-cutting Machines/ may be read with advantage.

"Cutting wood consists of two distinct operations; cross cutting the fibre, and splitting it off parallel to its lamination or grain.

"The two operations are in all cases combined; for to remove the wood both must be performed, and to go intelligently about the construction of machines and cutters, this principle must never be lost sight of. The greatest amount of power and the best edges are required to cross cut the fibre. To illustrate by a familiar example; To cross cut a block 12 inches square requires a considerable amount of effort and time, but a single blow will serve to split it in two, parallel to the fibre.

"This principle exists throughout the whole range of wood cutting with the same general conditions in all cases; a boring auger furnishes another example, different from the one given as an operation, but the same in principle.

"In boring, the main power is needed to cross cut the fibre with the spurs  or jaws  while the wood is split off and raised from the bottom of the hole without much effort; the spurs require frequent sharping, must have thin edges, and are soon worn away ; while the opposite is true of the radial or splitting edges, which may be blunt or dull, and yet work well enough and without much power.

"Another principle to be observed is that the cross cutting or cross severing of the fibre must precede the splitting process; the cross-cutting edges must act first and project beyond the splitting edges. There are no exceptions to this rule, which is from necessity carried out in most cases; yet it is not unfrequent to find tools working on the contrary principle, tearing instead of cutting away the wood.

"In some cases the wood is cross cut at such short intervals or lengths, that no splitting edges are needed, yet the operation is the same. A splitting saw is an example of this kind; each tooth cuts away its shaving, transverse to, or across the fibre, which is split off in the act of cross cutting without requiring separate edges. The cross-cut saw is an example of the same kind, although apparently different; the different shaped teeth that are required arise from the manner in which they are applied. With the ripping or slitting saw the plate is parallel to the fibre, and with the cross-cut saw it is transverse to the fibre; the cutting edges in both cases have nearly the same relation to and act in the same manner on the fibres or grain of the wood; in short, the difference between cross cutting and ripping saw teeth comes from the rotation being with or across the grain, and not from a difference in the operation of cutting.

"The line of the edge is parallel to the plate in cross cutting, and transverse to the plate in slitting. As before remarked all operations in wood cutting are the same in principle, and can be resolved into some such simple propositions as follow;

First. Wood cutting consists in two operations or processes; cross cutting and splitting.

Second. Tools for wood cutting must have independent edges directed to these two operations, unless the wood is cross cut into short lengths, as in the case of saws.

Third. The cross-cutting edges must project beyond those for splitting, and act first, as in grooving and tenoning heads.

Fourth. Cross-cutting edges will, if applied at an angle to the fibre, act with less power and be more durable.

Fifth. Splitting-edges act best when parallel to the fibre, but at an angle to the direction of their movement.

Sixth. Cutters for perforating, or end tools, as we will call them, should be arranged to have their action balanced across the centre whenever practicable, to prevent jar and vibration."

These propositions comprehend the whole system of cutter action, and as all wood manufacture is by cutting, they may also be said to comprehend all that is done in working wood.

We shall not attempt to show their application to planing, moulding, rabbeting, sawing, grooving, shaping and other cutters, the reader can observe this himself, and thus will acquire, if he has not already done so, a general idea of principles, that will guide him in making, setting, and arranging cutters for all kinds of work, without fear of making mistakes and without having to try whether this plan or that plan will work. It will also furnish a clue to the proper form of saw teeth, shearing knives, and other details, about which there is a great diversity of opinion.
 

While the operators of wood machines are not expected to construct their own cutter-heads, it is expected that they will furnish plans and instructions to others as to how they should be made, and as the angles at which the cutters act is an important matter in the making of machines, it
deserves some notice here.

The views given on the subject and the examples shown are not based upon theoretical inference so much as upon practical experiment. There are some very obscure conditions connected with the action of wood cutters; if they moved as slowly as metal-cutting tools we could observe and note the process of their action, but when in motion they are practically invisible, and nothing can be determined except by comparative experiments.

A general object among wood workmen seems to be to get as low or acute an angle for cutters as possible, regardless of the particular uses to which they are applied, and then to prevent slivering, or pulling out the wood, by means of caps. There are, of course, exceptions to this rule, especially with small cutter-heads, as in the case of shaping machines, but exceptions are generally necessary from the form of constructing the cutter-head rather than the result of any plans that have reference to the work. Never trouble with nor attempt to use caps on the cutters of power machines; they are expensive, inefficient to perform the intended purpose, and besides unnecessary.

Any kind of wood, including boxwood, rosewood, soft wood or green wood of all descriptions can be worked without caps, or chip breakers, as they are sometimes called, simply by giving the edges a proper angle, and attending to other conditions to be noted.

In planing veneers by hand it has long been demonstrated that the plane iron requires a much higher angle than for other work. It is also known that scraping tools with blunt edges are the only tools that can be used in turning hard woods or ivory ; in fact with all hand tools the principle of varying angles adapted to the work seems to be well known and generally applied, but when we come to power' tools we find planers and moulding machines made with their cutters at a constant angle, usually as acute as possible.

In determining the angle of cutters the following propositions are laid down;

1st. In cutting clean pine for surfacing, matching, or moulding, the angle of the cutters can be as low as practicable to clear a good washer and holding bolt with a standard head.

2nd. An acute angle requires a thin edge, and a thin edge cannot at the same time be a hard one, nor, for that reason, a sharp one, except in working soft clean lumber.

3rd. An edge may be hard, and kept sharp, as the angle is obtuse and the bevel short.

4th. In cutting thin shavings the operation is altogether cross cutting, and a sharp edge is more important than a thin one.

5th. As the angle of cutters becomes more obtuse, or higher, the shape of the edge approaches nearer to having the same profile as the work, and the cutters for moulded forms are cheaper and more easily made and kept in order than if at a low angle.

From these propositions we can deduce the following rules, which are recommended to operators when they have occasion to determine the angle and bevel of wood cutters.