In putting on the saw, it should be passed up to the collar, and c screwed home until it binds in the saw eye with enough force to bring the threads of c fairly in contact with those on the mandrel a, but if screwed home too tightly it may spring the saw, especially if the saw is a very thin one.
As c must be removed from the arbor or mandrel every time the saw is changed, the wear on its thread is great, and in time it becomes loose, which impairs its accuracy.
Fig. 3082.
This objection is overcome in the construction shown in [Fig. 3082], which is that employed by the S. A. Woods Machine Company. It is seen in the figure that the cone c fits externally in a recess in the collar b, and at the coned end also upon the plain part e of the arbor. The cone is hollow and receives a spiral spring s, s. When the saw is put on it first meets c, and as nut n is screwed up, the saw s and cone are forced along arbor e until the saw meets the face of b, and the clamping takes place. The strength of the spring s is sufficient to hold the saw true, and as the motion of cone c is in this case but a very little, therefore its wear is but little, which makes this a durable and handy device, while the saw cannot be sprung from over-pressure of the cone. Circular saws of large diameter, as from 40 inches upwards, are made a fair sliding fit upon their arbors or mandrels, and are provided with two diametrically opposite pins that are fast in the arbor collar.
The pins should be on diametrically opposite sides of the arbor, and an easy sliding fit to the holes in the saw, but they should not bind tight. Both pins should bear against the holes in the saw, and if both the pins and the holes in the saw are properly located, the saw will pass up to the collar with either side against the arbor collar, or in other words, the saw may be turned around upon the arbor.
If the pins, or either of them, bind in the holes of the saw, and the latter is forced on the arbor, it will spring the saw out of true, and when this is the case care should be taken in making the correction to discover whether it is the pins or the holes in the saw that are wrongly located. If it is the pins, the error will show the same whichever side of the saw is placed next to the arbor collar, while if the error is in the holes, the error will show differently when the saw is reversed on the arbor.
When a saw becomes worn, and its teeth require sharpening, the first thing to do is to joint it, that is to say, bring down all its teeth to the same height, which may be done by holding an emery block or file against it while the saw is running, care being taken to hold the block or file firmly, and to continue the process until the tops of the teeth run true.
The next operation is to gum and sharpen the teeth. Gumming a saw is cutting out the throats, or gullets between the teeth, so as to maintain the height of the tooth, and it follows that on saws that have sharp gullets (or in other words, saws in which the back of one tooth and the face of the next tooth join in a sharp corner), the sharpening process with the file may be made to also perform the gumming.