A Practical Course of Instruction in The Science of Horology Or The Construction and Repair of Time-Measuring Instruments
by Orville R. Hagans and D. L. Thompson
To test the slip for satisfactory condition, run the little fingernail along the faces and there should be a noticeable catching of the nail on the lines. A soft iron grinding slip will require frequent reconditioning as the oilstone paste used on it will cut the slip also.
A triangular grinding slip, such as that shown in Fig. 5, is superior to the square one for cylindrical pivot work for the reason that the angle of the edge is acute and will grind a clean square shoulder. In making this slip a rod of iron of 1/4" in diameter and about 4" in length is placed in a bench-vise in such a manner that about half of its length can be filed to triangular section, as it would be difficult to hold it in a vise to file it for its full length. The finishing of this slip is done in the same manner as that of the square one.
A flat grinding slip, such as shown in Fig. 6, is one on which the corners have been filed to. an acute angle, or relieved, which produces the same results as that of the triangular one. This slip is made of iron rod of 1/4" in diameter, or a flat strip of iron of 1/4"x l/8" in section, filed to the section shown in the drawing and finished in the same manner as the others.
A flat slip with rounded corners, which is used to grind coned pivots, is shown in Fig. 7. It is made in the same manner as the sharp cornered one and then the acute corners are rounded on a carborundum stone, after which it is finished the same as described above. One corner should be rounded with a small radius for small pivots and the other corn-er with a larger radius for the larger ones.
A tang could be filed on any of these slips and a handle, of about 1/2" in diameter and 4" in length, fitted with which it could be more easily held and used.
5. MAKING A BELL-METAL POLISHING SLIP
A bell-metal slip, such as shown in Fig. 8, is used to hold a finer abrasive paste, such as diamantine, saphirine, or rouge with oil mixed to a waxy paste, with which to polish pivots smoothly and brightly after grinding to 'size with oilstone paste on an iron grinding slip. It is made in the same manner as the flat grinding slip using either a rod of bellmetal of about 1/4" in diameter or a flat strip of about 1/4"x1/8" in section. This slip is to be finished, after filing to shape, on a strip of medium emery-paper and lined on coarse emery-paper. Two of these should be made, one with sharp acute edges and one with rounded edges of different radii, or one combining these features would suffice.
6. FILING TAPERED PINS
Taper filing, or the filing of iron and brass pins, is an operation for which the horologist has frequent use. It is done in a similar manner to that of filing cylinders. The wire to be filed is held in a pin-vise, such as shown in Fig. 9, the wire rotated in a tapered groove in a filing block, Fig. 2, and filed to a slight taper like that shown in Fig. 10. Pins filed to a needle point, Fig. 11, must be avoided as they cannot be depended upon to hold securely in their holes. A pin of any ordinary size can be readily produced in this manner and after filing to fit the hole properly it should be burnished lengthwise with a burnisher to remove the file marks and make it smooth. It is now placed in the hole again, twisted friction tight, marked for length with a sharp knife, after which it is removed, cut to length with nippers, the ends filed Or stoned flat and the edges slightly rounded. A pin made and fitted in this manner will hold securely in its hole and show good workmanship.
7. METAL SAWING
In using the jeweler's saw, the outlines of the part that is to be made are first marked, from a sample or from a drawing, on the metal to be used. The sawing of straight lines should first be practiced and to do this mark a straight line on a piece of sheet brass, of about 1/16" in thickness, and fasten it in a bench vise, allowing only a moderate length of it to extend so as to prevent it from springing or bending while sawing. Hold the thumbnail or the edge of the metal to assist in starting the saw on the line, after which handle the saw in much the same manner as you would file for flat filing. Hold the saw in the right hand and the end of the saw frame, close to the blade, with the thumb and forefinger of the left. Saw slowly with even and measured strokes, watching the saw and the line continually and releasing the pressure on the return stroke.
A saw blade should be tightened in the adjustable saw-frame until it is quite taut and the pressure used on it should be judged by the size of the blade and the hardness of the metal being sawed. A dull saw has lost most, if not all, of its off-set which causes it to bind in its cut.
This friction causes heating which expands the blade and causes it to stick in its cut and break. A slightly dull blade will not follow a line as readily as a sharp one and if one is to do much metal sawing it is well to have a good supply of blades on hand. Jeweler's saw blades are made in various sizes, running from quite fines ones to those of scroll saw size, and for practice work a medium sized blade should be selected.
When straight lines can be sawed in brass, then mark one on a piece of sheet iron, of about 1/32" in thickness, and continue the practice of this work until it can be done without difficulty.
Having learned to saw straight I lines easily, mark a circle on a piece of 'sheet brass, using a scriber-compass or a coin and a sharp pointed instrument, and saw it out in the same manner. Then repeat the operation on sheet iron. The only secret of sawing to a line, either straight or curved, by hand, is to use slow, measured strokes of the saw and to continually watch the saw and the line.
8. MAKING A PAIR OF PIERCED CLOCK HANDS
Making a pair of pierced clock hands, such as shown in Figs. 12 to 15, will give further practice in the use of files and saw and will prepare one for the work of making flat watch parts. Secure from a hardware store or machinist's supply house, two pieces of flat sheet iron of 1"x 6"x 1/32" in dimensions. This stock can be bought with finished or with unfinished surfaces. The former which is more expensive, has a flat ground finish while the latter is flat rolled stock which usually has a surface scale which is too hard to file or saw. This scale can be removed by grinding with emery-paper. When either is used the iron should be given a blue color so as to plainly show the lines of the design which is to be marked on it. This is done by holding the metal with a pair of pliers over the flame of an alcohol lamp, one with a half-inch wick will provide sufficient heat-and moving it back and forth, to evenly distribute the heat, until an even dark-blue color appears.
After bluing the iron the design of of the hand is to be marked on the metal, from a sample hand or from the drawings shown in Figs. 12 and 14. To copy the designs shown in the drawings, first making a tracing on tissue paper, then glue the tracing on the metal and mark the lines with a sharp pointed instrument, such as a point ground on a round file. The metal is then placed in a benchvise and sawed to outline, which is best done by starting at the end. The edges are then filed to line and then smoothed with a stone. Several small files of different shapes, such as a round and an oval file for inside curves, and a barette file, which has saw-edges, for acute corners, will be required for this work, after which holes are drilled to start the saw and the inside markings sawed and filed to line.
In practical work, the sockets from the old hands, if available and in good condition, can be removed and the new hands fitted to them. The new hands should be ground smooth with emery-paper and colored before being fastened to their sockets.
If a minute hand is to fit on a squared center-arbor or a squared cannon-pinion, of a striking clock then care must be taken in filing the square in the hand, or in fitting the squared socket to the hand, so that it will fit properly in relation to the striking pi~s in the center-arbor or cannon pinion. To file a square hole, first measure the diameter of the square it is to fit on and drill a hole of this diameter.
The hole is then squared by filing a little form one corner, then the next, and so on around the hole, as shown in Fig 10, trying it frequently on the square, until it fits nicely.
9. COLORING HANDS
After the hands have been completed and smoothed with emery paper, they can be colored red, purple, or dark-blue by heating. 'To do this, secure a flat piece of sheet iron of about 1"x 6" x l/16" in dimensions, and then straighten the hands until they will lay flat on the strip and in contact with it for their full length. Clean the hands with benzine to remove all grease and finger-prints so they will take a nice even color. Place a hand on the strip and hold it over the flame of an alcohol lamp, moving it lengthwise over the flame to evenly distribute the heat, until an even dark-blue color appears, then drop it in a dish of water. The iron will first take on pale yellow or straw color which deepens to a dark straw, then red, purple, dark-blue, pale-blue, and finally to greyish white again. If the hand does not color evenly on the first attempt, then brighten it with emery-paper, clean with benzine, and try again. Rusted or scratched iron or steel hands can be restored to their original color in this manner.
(to be continued)