The -inch hole to receive the end of the first broach was drilled in the stock, and the other end of the broach was inserted in the hole H in plate C, Fig. 293. To the plate was secured two rods, which had a vertical movement in plate B, light springs keeping plate C away from the punch. An important feature is the hole H, which received the end of the broach and prevented its being placed in the wrong position, as each broach had to follow exact, owing to the keyway.

A clearance (shown at D) on each broach served to guide an end of the broach while entering. After the first broach was entered and forced into the work by the press, the upper end

projected above the work to receive the second broach, which was in turn punched through, being followed by broach No. 3, and the latter by No. 4. If teeth were cut the full length of the last broach, it would stick in the work. To overcome this it was cleared at the end, as shown, so that when punched down to the end of the stroke the broach would fall through. The work in making broaches of this length is simple, as they are easy to turn, harden, draw, and grind.

In punch A a hardened-steel plate, D, was inserted, as at this point any wear would cause the broach to twist and spoil the key. This is made a driving fit, and can be replaced at any

time. The finished hole, Fig. 286, was drifted cold; and owing to the quality of the stock was a neat piece of work. Figs. 293 and 294 show the drift and the punch-press fixtures. The punch

for putting in the drift had a steel insert, the same as D in A. It is very important in making broaches that the stock be thoroughly annealed, and when broaching use nothing but the very best of oil.

SOME POINTS ABOUT BROACHES AND BROACHING.

In order to secure good results in broaching the bottom of the tool used should be hollowed out somewhat, so that a nice clean chip will be cut from the inside of the hole, and so that the tendency to dodge to one side when places in which the cored hole is rough or crooked are encountered will be obviated. The stripper for the work should be arranged so as to pull off square. Otherwise, if the hole is a long one, it will be spoiled when the broach is pulled out.

The special presses provided for broaching are usually backgeared and very powerful. It is not well to speed the press too fast. In all cases use oil as a lubricant. When the amount of

stock to be removed is considerable, it will be necessary to do the work in two operations; too heavy a cut having a tendency to make the hole rough. Socket-wrenches or similar fits are easily made in this way. If the cuts are made light enough, it is possible to broach cast-iron in this way, using for this purpose several punches or broaches of different sizes. Such punches should be slightly larger at the cutting end, and for the finishing cut or last operation-if clear through the piece-should work into a die or the tool will break off or tear away the lower edge of the work. The temper should be a trifle harder than that given to ordinary punches and dies. A in Fig. 295 shows a side view of a broach which was made for cutting out the holes in three cast-steel flanges for a steamboat. The holes had been cored out of a ğ-inch bolt instead of a 3-inch; hence the necessity for enlarging them. The broach was made with six steps, as

shown at A, and with the steps numbered at B. Step 1 acts as a pilot and to scrape out the sand; step 2 cuts on four sides somewhat, as shown at C, step 3 cuts the hole slightly larger in the same manner; the next three steps cut out the corners, as shown in 4, 5, and 6.

There were ninety holes in all, one-half of which were through metal-inch thick, and the other through metal §-inch thick. It took about three hours to broach them out, driving the broach with a sledge, as no press was at hand. The operation of making the tool took about one and one-half hours on the millingmachine, using an end-mill.

BROACHING: ITS RELATION TO SHEET-METAL

WORK.

Oberlin Smith, in his "Press Working of Metals," has given us the following in regard to the relation of the word "broaching" to sheet-metal work:

The word broaching' has here a very different meaning from that given it by the machinist, who applies it to the process of forcing a piece of male work through a lower cutting-die, or pushing a cutting-punch through a hole in female work, thereby shaving it to a given size, and really performing an operation analogous to planing or slotting. In cases where he uses male or female broaching-cutters having a series of teeth following each other, and each taking off its own chip, his work more nearly resembles milling. In relation to sheet metals the word broaching means smashing the work thinner by forcing it through a space between the punch and die, as in some kinds of tube-drawing, which again is the same as wire-drawing, if we imagine the mandrel to be a part of the tube. In the case in question a reduction of diameter is being made at the same time as the thinning of the metal is taking place. This is much practised in cartridge-drawing, especially where it is desirable to keep the end or bottom of the work of the original thickness. When done, the bottom remains of as much greater thickness than the sides as happens to be required and as has been arranged for in choosing the thickness of the sheet. In small work of this kind the use of a blank-holder, or upper die, is abandoned after the first one or two draws, as the metal is reduced so little in diameter in proportion to its thickness that the wrinkles have no chance to form. Even if incipient wrinkles do form they are quickly crushed out again as the metal is squeezed somewhat thinner. In this, as in all drawing, however, the wrinkles must never be allowed to get big enough to fold over upon one another."

CHAPTER XIX.

Shop Use of Micrometer-Calipers and the Height

Gauge.

MICROMETER-CALIPERS.

IN the accurate production of duplicate parts as carried on to-day in the economic manufacture of machinery, tools, punches and dies, and instruments of precision, accurate gauges are demanded. For years the average machine-shop got along with. templets and gauges of sheet steel, so-called "limit-gauges," of doubtful accuracy and of little value, as they were carelessly made and used with indifference. However, we are pleased to say, this state of affairs has passed away; and the increased use of the micrometer-caliper has enriched the scrap piles of many shops with collections of "snap" and "limit" gauges, "templets" and "reference" disks; has increased the economic production of the shops, and made the workmen more skilful.

To produce accurate work the skilled machinist or tool-maker of to-day demands as a first requisite a means of measuring his work during the process of machining it to the required size and shape; and this requirement is filled when the workman is supplied with a micrometer caliper and the feed-screws of the machine which he operates are fitted with graduated disks. Of course it must not be inferred from this that brains are not required along with these gauges; or that an indifferent or careless workman will instantly become a skilled mechanic upon being supplied with a micrometer. However, the use of the micrometer will improve the poorest workman; as instead of guessing he will measure; he will use his eyes and think; thus a consequent improvement will take place.

Among shop managers, superintendents, and foremen, the most common objection raised against the general shop use of micrometers is that they are too light, and are liable to get out