Modern Machine-Shop Practice Part 125

The face F of the tool is ground at an angle in the direction of I, so that the tool shall take its cut gradually, and that the whole length of the tool cutting edge shall not strike the cut at the same instant, which would cause a sudden strain liable to break either the tool or some part of the machine itself. So likewise the tool will leave its cut gradually and not with a jump. As shown in the cut, but a small part of the cutting edge would first meet the work, exerting for an instant of time only enough pressure and resistance to bring all the working parts of the machine up to a bearing, and as the tool descends (as denoted by the arrow G), the strain would increase until the whole length of tool cutting edge was in operation. For such heavy duty as this the tool is tempered down to a purple to give it strength.

CHAPTER XXI.--THREAD CUTTING.--BROACHING PRESS.

In Fig. 1809 is represented a front view of a patent die stock for threading pipe up to six inches in diameter. In the figure the three bits or chasers are shown locked in position by the face plate, which is shown removed in Fig. 1810. Fig. 1811 shows the machine with the face plate removed, the bit or chasers having pins in them which fit into the slots in the face plate, so that by rotating the plate the chasers may be set to size.

[Ill.u.s.tration: Fig. 1809.]

[Ill.u.s.tration: Fig. 1810.]

[Ill.u.s.tration: Fig. 1811.]

[Ill.u.s.tration: Fig. 1812.]

The head carrying the chasers is revolved by means of the gear-wheel and pinion, and Fig. 1812 represents a ratchet lever for revolving the pinion, and is useful when the pipe is in the ground and the die stock is used to cut it off and thread it without lifting it from its position.

[Ill.u.s.tration: Fig. 1813.]

The method of gripping the pipe is shown in Fig. 1813, in which the machine is represented as arranged for operating by belt power, the pinion being operated by a worm and worm-gear.

[Ill.u.s.tration: Fig. 1814.]

Referring to the pipe-gripping vice it is seen in the figure that the back of the machine is provided with ways in which the gripping jaws slide. The lower jaw is adjusted for height to suit the size of pipe to be operated upon, and is firmly locked in its adjusted position. It is provided with an index pointer, and the face of the slideway is marked by lines to suit the different diameters of pipe, so that this jaw may at once be set to the proper height to bring the pipe central to the bits. The lower jaw being set, all that is necessary is, by means of the hand wheel, to operate the upper one to firmly grip the pipe. Fig. 1814 shows the front of the machine when arranged for belt power.

The No. 1 die stock threads pipe from one to two inches in diameter, but has no cut-off. The large gear has cut teeth, and the pinion is of steel, working in gun-metal bearings. The gripping jaws are fitted with cast-steel faces, hardened.

By a simple change the stock may be used to cut left-hand as well as right-hand threads, this change consisting in putting in left-hand bits and in replacing the right-hand screw ring with a left-hand one. After a piece of pipe has been threaded, all that is necessary is to turn the head in the opposite direction, and the bits retire from the pipe thread, so that the pipe may at once be withdrawn, which preserves the cutting edges of the bits as well as saves the time usually lost in winding the dies back.

In threading machines the bolt (or pipe, as the case may be) may be revolved and the die held stationary, or the die may be revolved and the pipe held from revolving, the differences between the two systems being as follows, which is from _The American Machinist_:--

Fig. 1815 may be taken to represent a machine in which the pipe is held and the die revolved, and Fig. 1816 one in which the pipe is revolved and the dies are held in a head, which allows them to move laterally to suit the pipe that may not run true, while it prevents them from revolving.

In the former figure the bolt or pipe is shown to be out of line with the die driving spindle, and the result will be that the thread will not be parallel with the axis of the pipe. Whereas in Fig. 1816 the thread will be true with the axis of the work, because the latter revolves, and as the die is permitted more lateral motion it can move to accommodate itself to the eccentric motion of the work, if the latter should not run true.

If the end of a piece of pipe is not cut off square or at a right angle to the pipe axis, and the die has liberty to move, it will thread or take hold of one part, the longest one, of the pipe circ.u.mference first, and the die will cant over out of square with the pipe axis, and the thread cut will not be in line with the pipe axis.

[Ill.u.s.tration: Fig. 1815.]

[Ill.u.s.tration: Fig. 1816.]

The two important points in operating threading machines is to keep the dies sharp and to well lubricate them with oil. When dies are run at a maximum speed and continuously at work they should be sharpened once or, if the duty is heavy, twice a day, a very little grinding sufficing.

In nut tapping the oil lubrication is of the utmost importance, and is more difficult because the cuttings are apt to clog the tap flutes and prevent the oil from flowing into the cutting teeth.

When the tap stands vertical and the nuts are put on at the upper end (the point of the tap being uppermost), the cuttings are apt to pa.s.s upwards and prevent perfect lubrication by the descending oil. When the taps stand horizontally, gravity does not a.s.sist the oil to pa.s.s into the nut, and it falls rapidly from the tap, hence it is preferable that the tap should stand vertical with its point downwards, and running in oil and water.

In machines which cut the bolt threads with a solid die, it is obvious that after the thread is cut upon the bolt to the required distance, the direction of rotation of the bolt or die, as the case may be, requires to be reversed in order to remove the bolt from the die, and during this reversal of rotation the thread upon the bolt is apt to rub against and impair the cutting edges of the chasers or die teeth.

To obviate this difficulty in power machines the dies are sometimes caused to open when the bolt is threaded to the required distance, which enables the instant removal of the finished work, and this saves time as well as preserving the cutting edges of the die or chaser teeth.

In machines in which the bolt rotates, the machine must be stopped to take out each finished bolt and insert the blank one, which is unnecessary when the bolt is stationary, because so soon as the bolt is threaded to the required distance the dies may open automatically, the carriage holding the bolt at once withdrawn and a new one inserted.

When the dies open automatically the further advantage is secured that the bolts will all be threaded to an equal distance or length without care on the part of the operator.

[Ill.u.s.tration: Fig. 1817.]

A hand machine for threading bolts from 1/4 inch to 3/4 inch in diameter is shown in Fig. 1817. It consists of a head carrying a live spindle revolved by hand, by the lever shown at the right-hand end of the machine, being secured to the live spindle by a set-screw, so that the handle may be used at a greater or less leverage to suit the size of the thread to be cut; on the front end of this spindle are the dies, consisting of four chasers held in a collet that is readily removable from the spindle, being held by a spring bolt which, when pressed downwards, frees the collet from the spindle.

The work is held in a pair of vice jaws operated by the hand wheel shown, and this vice is moved endwise in its slideways on the bed by means of the vertical lever shown. The bolt being stationary, the small diameter of the die enables it to thread bent or crooked pieces, such as staples, &c.

For bolts of larger diameter requiring more force than can be exerted by a hand lever, a geared hand bolt cutter is employed.

[Ill.u.s.tration: Fig. 1818.]

In Fig. 1818 is represented a hand bolt cutter. In this cutter the bolt is rotated, being held in a suitable chuck. The revolving spindle is hollow in order to receive rods of any length, and is operated by bevel-wheels as shown, so as to increase the driving power of the spindle by decreasing its speed of rotation. To provide for a greater speed of rotation than that due to the diameters of the bevel-pinion and wheel, the lever is made to slide through the pinion, effecting the same object and convenience as described for the machine shown in Fig. 1817.

The threading dies are held in collets carried by a head or cylinder mounted horizontally on a carriage capable of being moved along the bed by means of a rack and pinion, the latter being operated by a handle pa.s.sing through the side of the bed as shown. The cylinder also carries a collet adapted for recessed plates so as to receive square or hexagon nuts of different sizes for tapping purposes, the taps being held in the rotating chuck. The collets are capable of ready and separate extraction, and by removing the collet that is opposite to the one that is at work, the end of a bolt may pa.s.s if necessary entirely through the head or cylinder threading the work to any required length or distance.

To insure that the die shall stand axially true with the revolving spindle, bolt holes are drilled in the lower part of the cylinder, and a pin pa.s.ses through the carriage carrying the head, and projects into these holes, which are so situated that when the pin end projects into a hole and locks the head a collet is in line with the spindle.

The dies consist of four chasers inserted in radial slots in collets held in place and bound together by a flat steel ring, which is let into the face of the collet and the external radial face of the chasers, and secured to the collet by screws. One chaser only is capable of radial motion for adjusting the diameter of thread the die will cut, and this chaser is adjusted and set by a screw in the periphery of the collet.

The other two chasers being held rigidly in a fixed position in the ring act as back rests and cut to the diameter or size to which they are made, or according to the adjustment of the first chaser. The shanks of the collets are secured in the cylindrical head by means of either a bolt and key or by a set-screw.

The chasers are sharpened by grinding the face on an ordinary grindstone or emery wheel.

[Ill.u.s.tration: Fig. 1819.]

The chasers are numbered to their places and are so constructed that if a single chaser of a set of three should require renewal, a chaser can be obtained from the manufacturers that will match with the remaining two of the set, the threads on the one falling exactly in line with those on the other two, whereas in other dies the renewal of one chaser involves the renewal of the whole number contained in the die. This is accomplished by so threading the dies that the thread starts from the same chaser (as No. 1) in each set.

In Fig. 1819 is represented one of these machines, which is intended for threads from 3/8 to 1 inch in diameter. It is arranged to be driven by belt power, being provided with a pulley having three steps; on this pulley spindle is a pinion operating a gear-wheel on the die driving spindle, as shown.

The oil and cuttings fall into a trough provided in the bed of the machine, but the oil drains through a strainer into the cylindrical receiver shown beneath the bed, whence it may be drawn off and used over again.

[Ill.u.s.tration: Fig. 1820.]

In Fig. 1820 is represented a bolt threading machine which is designed for bolts from 3/16 to 1 inch in diameter.

The bolt to be threaded is gripped in the vice L, operated by hand by the hand wheel M, and is moved by hand up to the head D, by the hand wheel Q operating the pinion in the rack shown at the back of the machine. When the dies or chasers have cut or threaded the bolt to the required distance, the threading dies are opened automatically as follows:--

At H is a clutch ring for opening and closing the threading chasers, and at N is the lever operating the shoes in the groove of the clutch ring.

This lever is upon a shaft running across the machine and having at its end the catch piece P; at Z is a catch for holding P upright against the pressure of a spring that is beneath the bed of the machine, and presses on an arm on the same shaft as the catch piece P. On the back jaw of the vice L is a bracket carrying a rod R, and the bolt or work is threaded until the end of rod R lifts catch Z, when the before-mentioned spring pulls lever N and clutch ring H forward, opening the dies and therefore stopping the threading operation. The length of thread cut upon the work is obviously determined by adjusting the distance rod R projects through V. The handle W is upon the same shaft as catch piece P and clutch lever N, and therefore affords means of opening the dies by hand.

The operation of the machine obviously consists of gripping the work in vice L, moving it up to the head D by the hand wheel Q, setting the rod R to open the dies when the bolt is threaded to the required length, and moving the vice back to receive a subsequent piece of work.

[Ill.u.s.tration: Fig. 1821.]