Woodworking machinery its rise, progress, and construction

The following pages, written in the spare hours of a busy life, attempt to give an account of the rise and progress of what is now in this country an important branch of engineering. Although wood is employed in the constructive arts more largely than any other substance, its conversion by machinery is of comparatively modem origin, and therefore very few books or treatises have been written on the subject. The aim of the Author has been to combine, as far as possible, the historical with the practical. In the first portion of the book, in addition to notes on design and construction, the names of the chief inventors and pioneers in woodworking machinery will be found; the latter part of the work is devoted entirely to practical and technical details.

The illustrations are confined to the designs of English, French, and American engineers, the machines constructed by other nations being, as a rule, based on these models.

The adaptation of machinery to common uses is, without doubt, increasingly necessary to the commercial prosperity and progress of a nation, and has been exemplified by the success of American competition in some branches of manufacture. This can in a measure be accounted for by the low patent fees and high rates of wages in vogue in that country, thus encouraging inventors to perfect the smallest details in their machine construction which tend either to lessen the cost of production, improve the quality or increase the range of the work performed. The saving thus effected may, in a day be infinitesimal, but when multiplied by months or years it assumes a gigantic total. This points, the Author takes it, to the urgent necessity of assimilating our own patent rates - which bear heavily on the brain power of the nation - to those of other countries.

From a somewhat extended practical experience of the subject treated on, the Author trusts that what he has written may afford some fresh information, and prove of service to the engineer and student. In that case his end will have been attained.

Many of our remarks on log band-sawing machines will apply also to those of ordinary construction, but we may say that, to make a really efficient machine, the main framing should be rigid and cast in one piece, and of a height not greater than is absolutely required for working. Hollow or box framing is to be preferred, but for light machines a stout flange casting may be sufficient; the base of the machine should be extended, and, given these, freedom from excessive vibration in working may be secured.

To insure easy manipulation of the wood, it will be necessary to bow the main frame sufficiently to allow of ample space between it and the saw. The next most important point is the construction of the saw wheels. These should be of as large a diameter as may be convenient, and combine strength with lightness in the highest possible degree, and be perfectly in balance. An elastic rubber band or cushion must also be provided for the saw to ride on.

In the best practice the old cast-iron flanged wheels have given place to light steel or wrought-iron ones, made somewhat after the fashion of bicycle wheels and without flanges. The top wheel is arranged to cant thus directing the saw to run on any part of the periphery and equalising the wear on the elastic covering. The top saw wheel must be mounted elastically, and the author has found for heavy machines two pairs of bearings - mounted in a slide for the top wheels and in standards or pedestals for the bottom wheel - to be preferable to single bearings or the plan of mounting the wheel to run on studs. To keep the saw to its proper tension, and lessen the breakage of the blades a weighted counterbalance lever, or a spring arrangement, must in all cases be fitted to the top slide. An extremely important matter is the guiding and supporting of the saw blade as it enters and leaves the wood; this may be done by fitting in the table metallic friction guide wheels to receive the back thrust of the saw, an adjustable wooden guide immediately beneath the table and a similar guide fitted in an adjustable counter-balanced slide fixed immediately above the surface of the wood.

The table must, of course, be arranged to set to angle: this is usually done by means of a slotted quadrant and stud, but the trouble of unslacking the nut and uncertainty of fixing the table may be obviated by forming a worm on the quadrant, and working it by a worm and hand wheel. The table can thus be set to any desired angle with the greatest nicety.

Before commencing work, the machine should be carefully fixed to a dead level, and it would be well to place beneath the base-plate a sheet of felt, as this has a tendency to absorb and lessen the vibration in working, especially if the machine be placed on an upper floor.


Why do band saws break, that is the question.

Many people would probably say because they are not strong enough ; but when we consider that the limit of endurance of a jointed and strained band saw blade is not less than 180 lbs. for every of its width, something beyond fair usage must account for their constant breakage. I take it the chief causes of breakage may be set down as follows:  

1. Improperly or badly constructed machines.
2. Bad saws.
3. Saws of too thick a gauge for the diameter of the wheels.
4. Saw wheels too small, too heavy, or out of balance.
5. Want of elastic tension in mounting the saw wheels.
6. Too great or sudden a tension, or wheel covering worn, or out of order.
7. In overcoming the inertia of starting the top wheel, and from the top wheel overrunning the bottom wheel and saw.
8. From the expansion of working and the omission to loosen the saw blade as it contracts after finishing work.
9. Improper method of receiving the back thrust of the saw.
10. From imperfect brazing and the joint being thicker than the other part of the blade.
11. From chips dropping between the blade and the bottom saw wheel.
12. Insufficient guides for the saw as it enters or leaves the cut.
13. Improper teeth or width of blade for the wood or work to be done.
14. Improper and uneven sharpening and setting.
15. Improper speed.
16. Improper working, such as forcing the saw, using dull saws, &c.

There may be other reasons for breakage than above, but these are the chief ones the writer can call to mind at the moment; practical readers can add to the list.

Referring to cause of breakage No. 1 on the list, we have already given some notes on the points to be desired in a well-constructed machine which will sufficiently answer this.

With reference to band saws (No. 2), the user has to a great extent to place himself in the hands of the saw-maker, as it is difficult to distinguish by inspection the quality or temper of a saw blade. By bending the blade or by setting some of the teeth coarsely you can in a degree judge its elasticity as to its temper, as, should it be too hard, it would probably crack. A blade either too hard or too soft is useless; what is required in a band saw is toughness, and a certain degree of hardness combined. (3) A fruitful cause of breakage of the blades is the use of band saws of too thick a gauge for the size of the saw wheels on which they run.The blades when in work are subjected to several severe strains the chief of which are bending and torsional; this is particularly the case when thick saws are run on wheels of small diameter as the arc of contact of the saw and wheel is too sharp. It is a mistake to use thick saws; a thin gauge saw will stand better than a thick one.

4. As we have elsewhere remarked saw wheels of small diameter are to be avoided. We prefer to run wheels without flanges on them. 5. A very important point in working band saws is to secure a constant and even tension on the saw blade ; at the same time the tension should be elastic, and not rigid, to allow for the expansion and contraction of the saw, as the friction of working sets up heat, which causes the blade to expand, and when the machine is at rest, and the blade becomes cool, it contracts again. Should the saw catch in a knot or nail and give a jump, if the top saw wheel is mounted rigidly it will almost invariably snap, but should it be elastically mounted it will give with the saw, and so save its fracture.

6. Some operators run their saws at too great a tension, and should this be suddenly increased by the saw striking some hard substance fracture is the result; or if the elastic saw wheel covering is allowed to get worn the saw becomes twisted in running and breakage often ensues. This latter can be avoided by arranging the top saw wheel to cant, and so leading the saw to any part of the periphery, and thus equalising the wear of the rubber covering. Should saws be run at too great tension, the excessive friction rapidly alters the granular structure of the steel, which becomes crystallised and soon cracks and fractures.

7. In working band-sawing machines it is important that they should be set in motion gradually, more particularly where the wheels are of the old fashioned type and heavy, as it takes a little time to overcome the inertia of the top saw wheel, and if the power is applied all at once there is a considerable tendency to snap the blade from the sudden strain put upon it.

A fruitful cause of breakage of the blades is the overrunning by the top wheel of the bottom or driving wheel of the saw, and also of the saw itself. When the top saw wheel is running at full speed it necessarily acquires a considerable momentum, and acts somewhat after the fashion of a fly wheel; consequently, when the speed of the saw blade is suddenly checked by its entry into the wood as it commences to saw, the acquired momentum of the top wheel not being checked in a like proportion overruns the saw and the driving wheel, and creeps, so to speak, up the back of the saw, and consequently buckles or breaks it at the point of resistance, viz. where the saw enters the wood.

8. Saw blades should in all cases be slackened out after finishing work. Notwithstanding the small area of the blade in frictional contact with the wood and the constant cooling action of the air through which the saw passes, a considerable amount of heat is often engendered in the blade, especially in sawing resinous or difficult woods. Consequently, the blade expands considerably, and the slack is taken up by the operator. When the work is over, and the friction on the blade removed, it immediately commences to contract.

9. Another cause of the breakage of the blades is an improper method of receiving their back thrust. The best way to do this has been the subject of considerable discussion. We prefer to fit revolving steel discs for this purpose, as the back of the saw blade does not so readily cut into them as with fixed ones. If a disc is allowed to get deeply grooved, the blade gets buckled and twisted, and often breaks.

10. Imperfect brazing is another cause of breakage. To secure a steady and even motion on the saw blade, it is important that the brazing be carefully and neatly done (see p. 338).

11. Chips may be prevented dropping between the saw blade and the bottom wheel by attaching an angular guard to the frame of the machine.

12. No comment is needed with respect to insufficient guides.

13. The proper shape and pitch of the teeth is a matter of great moment in the successful working of band saws. Should teeth be used unsuited to the wood being cut, a largely increased friction on the blade is set up, the teeth are rapidly dulled or broken, and the work turned out is inferior. For sawing all ordinary woods of the Pinus family ordinary hand saw teeth are suitable except for pitch pine; for working this wood coarsely spaced and set teeth are suitable. We can recommend for durability saws with gullet teeth, that is, rounded at the root, as they are less liable to fracture than saws with the roots running to an angle, as the fracture in the blade is found almost invariably to commence at the point of this angle. Owing, however, to small gullet teeth being more troublesome to sharpen, the hand saw. teeth are now largely employed. For sawing oak, ash, elm and hard woods generally, more teeth or points, say five or six to the inch, should be used, and these filed farther back.

14. Care must be taken that the saw teeth, are uniformly set and sharpened. Uneven and improper setting causes a considerable amount of tension to the saw blade, increased friction crystallising the steel, and consequent breakage. The teeth of band saws should by preference be set by light, carefully given blow, instead of bending, which, unless very carefully performed, is more liable to buckle the blades and prevent them running true. Several little machines are now made, by which saws can be accurately set to any desired coarseness by a blow similar to that given by a hammer instead of by a bending pressure.

15. The speed at which the saw blade travels has much to do with its cutting efficiency. Saws running on small wheels say, below 3 ft. diameter cannot be run with safety so fast as on larger wheels.

16. We need hardly say a bad workman may break any amount of saws by forcing them, bending them edgeways, using dull saws, or saws too wide or stout for the work, &c. If in working a properly sharpened and set blade should have a tendency to bind, it probably arises from insufficiency of throat room in the teeth. It would be well, therefore, to try a saw with the teeth set a little further apart: this will not cut quite so fast, but the sawdust will have time to escape, and the binding should be done away with.

In concluding our remarks on working band saws, there is little doubt that - given in the first instance a well-constructed machine, a careful operator, and a saw blade uniform in gauge, width, toothing, sharpening, setting, and temper - a band sawing machine is one of the most money-earning and valuable of all wood-working machines, not only for the ordinary curved work, for which it is generally used, but for breaking down heavy logs.