CIRCULAR SAWS.

Press, Volume LXI, Issue 18287, 22 January 1925, Page 5

CIRCULAR SAWS.

THEIR VARIED USES, When a carpenter or joiner consider* that it is time he should add to hip working capacity, he usually buys a circular saw bench, and either an electric motor or a small gas engine to drive it. In some cases he obtains full value from his investment; in many ho fails to use many of the modern circular saws- used for cutting wood. In many instances the saw bought does not give the greatest satisfaction. For example, it is quite a common thing to find a circular saw, with very email teeth, being used in a builder's shop. The saw is run very fast under the impression that by so doing the cutting speed is increased. Several times I have had complaints about circular saws which cut badly, and found that the trouble was the teeth were no more than Jin from point to point, aad the 14jn or larger paw was run at from 2090 to 2509 revolutions a minute. The speed was go great that the cutting points of the saw did not get a grip of the wood, Reducing the speed to 1500, and knocking put every other tooth, made that saw a cutting tool which would tackle the wood as fast as it could be taken to the saw. Sawmakers work on a wrong theory; they consider that a certain number of teeth should go in a saw. If it 1b a 72in saw it should have fifty teeth, if it is a 12in saw jt should have the same number irrespective of What the saw has to cut. This- is not borne out by practice. The number of teeth should be govcrned'by what kind of wood is to be sawn. If cutting soft woods, teeth sin from point to point will give better results in a saw than teeth {in from point to point.

Cutting Hard Woods. If cutting hard woods, increase the number of the teeth, as it lessens the strain upon the gaw. A tooth should cut ail the time ;t is in the wood. Many teeth in a saw does not allow this, as each does go little as they follow one another that they scrape instead of bite. The best putting paws,-are those with inserted teeth,. These an pot accessary for ordinary joinery work. I mention it because it explains a theory, Most circular saws have teeth which are better jadppted for scraping thaw cutting. The average carpenter, indeed,, one might-say sawyer, does not . realise the action pf the teeth of a circular saw, They imagine that a sharp point on the tooth of a saw is best fpr its working. Ono is surprised to find bow this idea is prevalent throughout the country. ' Even in mills which have been established a good while, they lower the working capacity of the mill by giving tho teeth of the saws acute points. The Americans sharpen their saw teethe flat, b»ve. no bevels on tho tops- Many experiments have proved to Jtte that » very slight bevel on the top of the teeth, go one tooth is bevelled ono side, the next tho other, makes the saw cut freer than if the tops were flat. It is a mistakes idea to imagine that if the top of the tooth is an acute angle, say, from tjie point to the bottom of; the gullet, that it is best for putting purposes. It is npt, as a matter of fact, it only makes n very slight difference to the cutting, capacity of the saw. An examination of the inserted tooth will explain how it cuts so freely. TJip tooth has a vpry sharp angle below the point. The average saw sent out with a saw bench has the teeth with very little rake, or hoojf, just the slightest inclination, The inserted tooth has the top so it just clears the cutting lino, and the point very thin, because the, part which runs to tho gullet is a very tieuto angle. This makes a great difference in tho jn tho sawing capacity of tho circular. Have a sharp rako on the tooth, tho top high, so it just clears the cutting line, and, if it be used for soft woods, not toojinany teeth. If you have a great many teeth in a saw used for ripping purposes, do not run it top fast; if you reduce the number of teeth, regulate the speed of tho saw, so it will cut as fast as you can present the wood. I need not mention that correct sharpening of the teeth is necessary to obtain these ideal conditions, How to sharpen a saw so it will work as described must be dealt with, iu another article. A man who is not used to circular saws should not use a very thin one. It is best to have a thicker one, say, an lfJin circular, thirteen gauge, and ask the saw-maker to tension it so it wlil - work without j packings. Sawyers w the States never use packings for their circular saws; they have them tensioned so at a definite speed they ran stiff enough to do j any kind of sawing. It is outside the! scope of this article to explain how it j is done; tho saw-maker should know, |

ad can make your saw so that it will work under such conditions. The builder may often require to cut a great number of thin strips, and not waste 0 great deal of material jn bo doing. What is needed is a swage saw. This is a saw which is thick at the spindle then ground on the fence side to a thin edge. It would be more correctly described as a taper paw. more especially as the word swaged is also used fpr describing the teeth being spread at the points instead of being set. However, the word has now passed into eoipmon use > and a swaged saw means a taper one.

The Swage Saw. Such a saw is exceedingly useful for many purposes. It will cut up to fin boards comparatively easily with no more waste than a frame saw. Using the top of the saw, Jin boards can Jje cut so thpy do viot lose more than l-32in of their width in the sawing- For instance, as the average 3aw does not take a foil 1-IG, go two pieces will not Jose more than l-32in. In many_ instances this means the saving of a great deal of wood, as a board can be entirely worked up into the job, instead of the outside one being put aside as too narrow.

The swage saw, if used by an ordinary workman, should not be ordered too thin. If an 18in saw is decided upon, have one eighteen gauge at the teeth, ten gauge at the spindle, the taper to be on the fence side, and the teeth to be lin from point to point, and tlio gullet not more than -Jin deep. When using theso saws for deeping, the tendency of the saw is to cut thick. The thicker the board you are cutting the greater the possibility of the saw to cut a thicker board than what the 'fence is set for sawing purposes. This is regulated by the ggt and the lead of tli? saw. Put more set on the fence side, and if this does not make the board parallel let that range of teeth be higher than the outside ones. This 5s called the lead of the saw, and it is 3 better method of regulating the sawing capacity tlum setting the teeth xjut tco much on one side. With a little practice it will soon be discovered how much lead and set are necessary for cutting various-sized boards. ,If you cut Jin ones, you will require more on the fence side than if_ you cut -Jin ones. When you realise this, and work the saw accordingly, it will go a good way tpwarda making the swage saw a successful one in a saw bench. One of the most useful saws which can be used in a small saw bench is what is known as a dimension, or hollow-ground one. This saw is just the reverse of a ground-off or swage saw, inasmuch that ft is thicker at the cutting edge than at the spindle.

Hollow-Ground Saws. The saw is used for cross-cutting wood blocks or other wooden articles which have to be cut as smoothly as the planed sides. By having a certain amount of rake on the teeth it is possible to use these saws so they will cut and leavo a sawn surface which will not require planing. The saw is ground on each side up to the part which goes 011 the spindle. Yarious men have different opinions as to,tho amount of grinding which should be applied to the saw. ltcally it depends on the size of the saw. A small one need not-be ground so much as a large one. It is best to use small saws, as they can be more easily kept in proper condition than a large one, A 12iu saw will do a great deal of useful sawi.»g, and cut up a quantity of wood which will not require planing. Such a saw should be about twelve or thirteen gauge at ihe teeth and seventeen gauge at the spindle. What is most important to obtain accurate results is the sharpening. It is ridiculous to expect that the saw, unless it is properly sharpened, will saw wood so it need not" be planed. It will not do so, and in a very short time it will be buckled and useless. \VJiile the sharpening is comparatively oasy, if caro is taken, it is difficult if it is undertaken in a haphazard manner. Every tooth must be made to cut an equal amount, This is ppssiblo providing great care is taken in the sharpening, Not only that, as the saw is used without any set, the front of tho teeth have to bo sharpened so the edgo is very sharp. No blurred edges arc possible for working conditions with theso saws, otherwise they will bind aud burn in tho wood, Carefully worked, it is remarkable what a saving such a saw will make in tlio work in a joiner's or carpenter's shop.

A crystal set in- a watch-case,. and another in a minute ring-box, but capable of receiving Chelmsford, 140 miles away, wers among the novelties at the British Wireless Exhibition in London. A Morse code recorder has been made by a London amateur from n needle-box, bicycle wheel spokes, a gramophone motor, and tho lid of a tin box.