Fig. 2.
When the square is in position, mark a line across the tin with the scratch awl held closely to the blade. Cut away the extra tin and you have two sides of your piece of tin squared. Proceed in the same manner to trim off the other end. The remaining or long side of the piece may be squared up either by using the ruler or the spring dividers. The strip of tin that you have squared up on three sides will probably be narrower at one end than at the other. Measure the width of the narrow end with the ruler and then measure off this same distance at the opposite end and mark it with the scratch awl. Use the ruler to connect the two measuring points and scratch a line in the tin by drawing the scratch awl along the edge of the ruler. Cut away the surplus tin and your piece of tin should be squared.
The spring dividers may be opened so that the points rest exactly on each corner of the narrowest end of the strips of tin. Then the dividers are moved to the opposite end of the strip and the lower end or point of the dividers moved back and forth slightly until a slight scratch is made in the surface of the tin to indicate the measuring point. The position of the dividers is shown in [Fig. 2]. The ruler is used to connect the two measuring points and a line scratched between them.
Small strips of tin may be marked off entirely by the dividers by setting the dividers to the required dimension, placing the dividers so that one point rests against one edge of the strip to be marked off and then drawing the dividers along in such a manner that the point of the dividers that rests on the tin will scratch a line parallel to the edge. The edge of the tin that the point of the dividers rests against must, of course, be cut straight before beginning the marking operations. The strip thus marked off may be cut away and another one marked off in the same manner until the required number of strips is cut.
Suppose that four strips are to be cut, each strip to measure one by ten inches. Square up a piece of tin to measure four by ten inches. Open the dividers so that the points are exactly one inch apart. Rest one point of the dividers against one edge of the tin as shown in [Fig. 2] and draw it along the entire length of the tin so as to scratch a line parallel to the edge. Cut off this strip, taking care to make a straight cut and then mark off another strip and cut it off, and so on until all four strips are cut. This method of using the dividers for marking is more accurate and much easier than that of using a ruler to measure off each strip, and certainly more rapid.
Finding Wheel Centers with the Dividers.—When making wheels of tin cans, some easy method must be used to find the center of the wheel in order to punch or bore a hole for the axle so that the axle may be placed as near the center of the wheel as possible, and so that the wheel will run true once it is placed on the axle.
The dividers may be used for this operation which is very simple. The can is first made up into wheel form as described in [Chapter X, page 108]. When the wheel is soldered together lay it flat on the bench. Open the dividers so that one point rests against the rim of the wheel or against the rolled edge of the can forming the rim of the wheel. If the wheel is made of a can that has a cap soldered on each end and this cap forms the end of the can (such as the small cans that are used for evaporated milk), then the one leg of the dividers may be rested in the slight line or depression just inside the rim that is invariably found in this can. Open the dividers so that the other point rests as near the center as you can guess it. When the dividers are set to dimension and are in position on the wheel as shown in [Fig. 3], then move the point of the dividers that is near the center of the wheel slightly back and forth so that it describes a slight arc and scratches it in the surface of the can and the other point of the divider is held at the point near the rim of the wheel during this operation. Then move the dividers directly across the wheel still set at the same dimension, placing one point against the rim or in the depressed line and describing a slight arc in the tin as before. Set the dividers at right angles to the first two marking points having the dividers still opened to the same dimension as at first and describe another arc. Set the dividers directly across from this point and describe another arc. The wheel should then resemble [Fig. 4], the four arcs forming sort of a pillow shape as shown. Draw lines diametrically across connecting each corner of the pillow as shown and where these lines cross is the center of the wheel.
