Modern Machine-Shop Practice Part 126

[Ill.u.s.tration: Fig. 1822.]

The construction of the head D and clutch and ring H is shown in Figs.

1821 and 1822.

The body F is bolted by the f.l.a.n.g.e I to a face plate in the live spindle or shaft of the machine, and through slots in this body pa.s.s the holders or cases C containing the chasers or dies. Upon F is the piece D provided with a slot to receive the die cases and a tongue to move them.

This slot and tongue, which are shown at E', are at an angle to the axis of F; hence if D be moved endways upon F the cases and dies are operated radially in or through the body F. To operate D laterally or endwise upon F the clutch ring H and the toggles G are provided, the latter being pivoted in the body F, and H being operated endwise upon F by the lever shown at N in the general view, Fig. 1820. The amount to which the dies will be closed is adjustable by means of the adjusting screws E, which are secured in their adjusted position by the set-screws R, Fig.

1821; it being obvious that when H meets the shoulder S of G and depresses that end of the toggle, head D is moved to the right and the dies are closed when the end of G meets E, and ceases to close when G has seated itself in F and can no longer move E. The backward motion of the clutch ring H, and therefore the amount to which the dies are opened, is regulated by the screw B and stop A in Fig. 1822, it being obvious that when B meets A the motion of H and D to the left upon F ceases and the dies are fully opened. The amount of their opening is therefore adjustable by means of screw B. J is simply a cap to hold the dies and cases in their places.

[Ill.u.s.tration: Fig. 1823.]

In the end view, Fig. 1823, E, E are the adjustment screws for the amount of die closure, and B, B those for the amount they will open to, T representing the screws for the cap J, which is removed for the insertion and extraction of the dies and die cases.

[Ill.u.s.tration: Fig. 1824.]

The construction of the dies P and cases C is shown in Fig. 1824. Two screws at N secure the dies in their cases and a screw M adjusts them endways so as to set them forward when recutting them. By inserting the dies in cases they may be made of simple pieces of rectangular steel, saving cost in their renewal when worn too short.

[Ill.u.s.tration: Fig. 1825.]

Fig. 1825 shows the machine arranged with back gear for bolts from 2 to 2-1/2 inches in diameter, the essential principles of construction being the same as in Fig. 1820.

[Ill.u.s.tration: Fig. 1826.]

In Fig. 1826 is represented a single and in Fig. 1827 a double "rapid"

machine, constructed for sizes up to 5/8 inch in diameter, the double machine having a pump to supply oil to the dies. This pump is operated by an eccentric upon the end of the shaft of the cone pulley.

The construction of the head of this machine is shown in Fig. 1827A. Z is the live or driving spindle, upon which is fast the head A. In A are pivoted at M the levers L which carry the dies D, which are secured in place in the levers by the set-screws B and adjusted to cut to the required diameter by the screws E. The levers L are closed upon the clutch C by means of the springs R and S, each of these springs acting upon two diametrically opposite levers, hence the action of the springs is to open the dies D. The clutch C has a cone at T and slides endways upon the live spindle Z. The clutch lever and shoes are upon a shaft running across the machine and actuated by a rod corresponding to the rod R in Fig. 1820. When the clutch and levers L are in the position shown in the figures the dies are closed for threading the bolt, and when this threading has proceeded to the required distance along the work, clutch C is moved by the aforesaid rod and lever in the direction of arrow W, and the springs R, S close the ends P of lever L down upon the body X of the clutch opening the dies and causing the threading to cease.

[Ill.u.s.tration: Fig. 1827.]

[Ill.u.s.tration: Fig. 1827A.]

Fig. 1828 represents a "double" rapid machine for threading work up to four inches in diameter, and therefore having back gear so as to provide sufficient power. The gauge rod from the carriage here disengages a bell crank from the end of the long lever shown, and thus prevents the spring to operate the cross shaft and open the dies.

In Fig. 1829 is represented a bolt threading machine or bolt cutter, which consists of a head carrying a live spindle upon which is a head carrying four bits or chasers that may be set to cut the work to the required diameter, and opened out after the work is threaded to the required length and the bolt withdrawn without losing the time that occurs when the dies require to run backward to release the work, and also preventing the abrasion and wear that occurs to the cutting edges of the die bits or chasers when revolved backward upon the work. This head is operated by the upright lever shown in the figure, this lever being connected to the clutch shown upon the live spindle. The details of construction of the clutch and of the head are shown in Figs. 1830, 1831, 1832, and 1833. The work to be threaded is gripped between jaws operated by the large hand wheel shown, while the vice moves the work up to or away from the head by means of the small hand wheel which operates pinions geared with racks on each side of the bed of the machine as clearly shown in the figure.

Fig. 1830 is a longitudinal section of the head, and Fig. 1831 an end view of the same. P are the threading dies or chasers held in slots in the body _a_ by the annular ring face plate K. The ends of the dies are provided with [T]-shaped caps T fitting into corresponding grooves or slideways in the die ring B, and it is obvious that as the heads of their caps are at an angle therefore sliding the ring B along _a_ and to the right of the position it occupies in the figure will cause the dies P to close concentrically towards the centre or axis of the head _a_. At C is a ring capable of sliding upon _a_ and operated by the upright lever shown in the general view in Fig. 1829.

The connection between the die ring B and the clutch ring C is shown in Figs. 1832 and 1833, the former being also a longitudinal sectional view of the head, but taken in a different plane from that in Fig. 1830. The barrel or body _a_ _a_ of the head is provided with two diametrically opposite curved rocking levers which are pivoted in recesses in _a_ _a_.

The clutch ring C envelops body _a_ and pa.s.ses between the curved ends of these rocking levers. The upper of the two rocker levers shown in the engraving connects with a lever E, which connects to a stud or plunger P, threaded to receive the adjusting screw I, which is threaded into the die ring B. Obviously when C is moved to the right along _a_ it operates the rocking lever and causes B to move to the right and to close the dies upon the work. The amount of die closure, and therefore the diameter to which the dies will thread the work, is adjustable by means of the adjusting screw I, which has a coa.r.s.e thread in B and a finer one in P, hence s.c.r.e.w.i.n.g up I draws B to the left and farther over the plunger P, thus shortening the distance between the centre of the curved lever and limiting the motion of B to the right. On the other hand, uns.c.r.e.w.i.n.g I moves B to the right, and it is obvious that in doing this the cap T in Fig. 1830 is forced down by the groove in B and the dies are moved endwise towards the axis _a_ _a_, or in other words, closed.

It will be clear that a greater amount of power will be necessary to hold the dies to their cut than to release them from it, and on that account the lower curved rocking arm D connects through E to a solid plunger G, the screw H ab.u.t.ting against the end of G and not threading into it, because G is only operative in pushing B forward in conjunction with P, while P pulls B backward, the duty being light. It is obvious, however, that after the adjustment screw I is operated to set the dies to cut to the proper diameter, adjustment screw H must be operated to bring the ring B fair and true upon _a_ _a_ and prevent any lateral strain that might otherwise ensue.

[Ill.u.s.tration: Fig. 1828.]

[Ill.u.s.tration: Fig. 1829.]

These two adjustments being made the clutch ring C is operated to the left to its full limit of motion to open the dies and to its full limit to the right to close them.

It will be seen, by the lines that are marked to pa.s.s through the pivoting pins of the rocking lever D, that the joints marked 2 in Fig.

1832 are below these lines, and as a result the links E form in effect a toggle joint locking firmer in proportion as the strain upon them is greater.

Fig. 1834 represents a bolt threading machine having two heads each of which is capable of threading bolts from 1/2 up to 1-1/2 inches in diameter.

[Ill.u.s.tration: Fig. 1830.]

[Ill.u.s.tration: Fig. 1831.]

[Ill.u.s.tration: Fig. 1832.]

[Ill.u.s.tration: Fig. 1833.]

[Ill.u.s.tration: Fig. 1834.]

The levers for operating the clutch rings are here placed horizontal, so that they may extend to the end of the machine and be convenient to operate, and a pump is employed to supply oil to the dies.

The capacity of a double machine of this kind is about one ton of railroad track bolts per day of 10 hours' working time.

In American practice it is usual to employ four cutting dies, bits, or chasers, in the heads of bolt threading machines, while in European practice it is common to employ but three. Considering this matter independently of the amount of clearance given to the teeth, we have as follows:--

If a die or internal reamer, the cutting points of which were all equidistant from a common centre, were placed over a piece of work, as a bar of iron shown in Fig. 1835, and set to take a certain cut, as shown by the circle outside the section, it is evident that if revolved, but left free to move laterally, or "wabble," the cutter would tend to adjust itself at all times in a manner to equalize the cutting duty--that is, if the die had two opposite cutting edges or points, and the piece operated upon were not of circular form, then, when one cutter reached the part that was not round, it would have either more or less cutting to do than before, and hence, the opposite cutter having the same amount, the tendency would be for the two cutting edges to travel over and equalize the cuts, and hence the pressure. With three cutting points, no two being opposite, the tendency would all the while be to equalize the cuts taken by all three; with four, s.p.a.ced equally, the tendency would always be to equalize the cuts of those diametrically opposite; with five, the tendency would be to equalize the duty on each, and so on. Thus it will be noticed that there is a difference between the acting principle of a die having an even or an odd number of cutters, independent of the difference in the actual number of cutting edges, or points, as we are now considering them.

[Ill.u.s.tration: Fig. 1835.]

[Ill.u.s.tration: Fig. 1836.]

To take an example, in Fig. 1835 is represented a die having four cutting points, placed upon a piece of iron of a round section, with the exception of a flat place, as shown. Now, in this position each one of the cutting points A, B, C, and D, is in contact with the true cylindrical part of the work only; hence, if the die were set to take the amount of cut shown, each point would enter the iron an equal distance, and the inner circle through the points would be the smallest diameter of the die. Upon revolving the die in the direction denoted by the arrow, an equal cut would continue to be taken off, and hence the circular form maintained, until cutter D had reached the edge _x_ of the flat, the opposite one B, being at _y_ (A at _r_ and C at _v_), proceeding as D moved from _x_ towards A, its cutting duty would continually become less and its pressure decrease, but as it is the cutting pressure of D that holds the opposite point B to its cut, as the pressure in D, after reaching _x_, continually becomes less, the die would gradually travel over so as to carry D toward the centre and cause it to take more cut, while B, on the opposite side, would travel out a corresponding distance and take less, thus keeping the duty equalized until the cutter D had reached H, the lowest part of the flat, when the die would have moved the greatest distance off the centre, a.s.suming the position shown by dotted lines. Thus the cutting point at H has pa.s.sed inside the true circle that all the cutters commenced to follow, while F has pa.s.sed outside. Meanwhile, as H and F have shifted over, E and G have, of course, moved an equal amount and in the same direction, but the diameter of E and G being at right angles to that of H and F, the distances of E and G from the centre would be changed but an infinitesimal amount; hence, they would virtually continue to follow the true circle, notwithstanding the deviation of the other pair. As the die continues to revolve and H pa.s.ses toward A, the lateral motion is reversed, the die tending to resume its original central position, which it does upon the completion of another quarter of a revolution, when the cutter that started at D has pa.s.sed to H and finally to A. A cutting has now been removed from the entire circ.u.mference of the iron, leaving it of a form shown approximately in Fig. 1836, where A _z_, B _y_, C _v_, and D _x_, are the four true circular portions cut respectively by the points A, B, C, and D, before the flat place was reached. After the flat place was reached _x_ A is the depression cut by D, _y_ C the elevation formed by B, and _z_ B and _v_ D are the arcs, differing almost imperceptibly from the true circular ones cut by A and C.

[Ill.u.s.tration: Fig. 1837.]

[Ill.u.s.tration: Fig. 1838.]

Fig. 1837 represents a die having three instead of four cutting points--that is, the point C of Fig. 1835 is left out, and the remaining ones A, B, and D, are equally s.p.a.ced. This, placed upon a similar bar and taking an equal cut, would produce a truly circular form until D had reached _x_--with A and B at _z_ and _y_--after which the die would move laterally, tending to carry D toward the centre of the work and A and B away from it, so as to equalize the cuts on all three. Hence, when D had reached H and the three-cutter die attained the position shown by dotted lines in Fig. 1837, H would have made an indentation inside the true circle, while E and F have travelled away from it, thus forming protuberances. From H to A the lateral movement is reversed, and finally upon the completion of a third of a revolution, the die is again central and a cut has been carried completely around the bar, leaving it as shown in Fig. 1838. Comparing this with Fig. 1836, it will be seen that there are three truly cylindrical portions--viz., A _z_, B _y_, and D _x_ instead of four in Fig. 1836, but each one is longer; that there is a depressed place, _x_ A, of equal length to that in Fig. 1836, and two elevations, _z_ B and _y_ D, each of equal length to the one (_y_ C) in Fig. 1836.

[Ill.u.s.tration: Fig. 1839.]

[Ill.u.s.tration: Fig. 1840.]

[Ill.u.s.tration: Fig. 1841.]

Now, suppose the bar to have an equal flat place on its opposite side, becoming of a section shown in Fig. 1839, upon applying the dies and pursuing a similar course of reasoning, the die with four points would reduce the bar to the size and shape shown in Fig. 1840, or a true cylinder, while the triple-pointed cutter would produce the form shown in Fig. 1841, which is a sort of hexagon, coinciding with the true circle in six places--A, _z_, B, _y_, D, and _x_--while between A and _z_, and opposite, between _y_ and D, there is an elevation; also from _z_ to B and from D to _x_. A flattened portion, A _x_, with a similar one B _y_, opposite, completes the profile. Suppose, now, that a bar of the form shown in Fig. 1842, having two flat places not opposite, be taken, and the four-cutter and three-cutter dies are applied. The product of the four is shown in Fig. 1843, and that produced by the three-cutter die in Fig. 1844. The section cut with four coincides with the true circle at four points, A, B, C, D, and differs from it almost imperceptibly at _z_, _y_, _v_, and _x_. There are two elevations between A and B and between B and C; also two depressions between C and D and between D and A. The section from the three-cutter die is the perfect circular form between A _z_, B _y_, and D _x_, with a projection from _z_ to B and two depressions from _y_ to D and from _x_ to A. The four-die, applied to a section having three flats like Fig. 1845, would produce Fig. 1846, which does not absolutely coincide with the true circle at any point, although the difference is inconsiderable at A, _z_, _y_, C, _v_ and _x_; three equidistant sections A _z_, _y_ C, and _v_ _x_, are elevated and the three alternate ones depressed.

[Ill.u.s.tration: Fig. 1842.]

[Ill.u.s.tration: Fig. 1843.]

[Ill.u.s.tration: Fig. 1844.]

[Ill.u.s.tration: Fig. 1845.]