Modern Machine-Shop Practice Part 106

The following, on some experiments upon the elasticity of wires, is from the report of a committee read before the British a.s.sociation at Sheffield, England.

"The most important of these experiments form a series that have been made on the elastic properties of very soft iron wire. The wire used was drawn for the purpose, and is extremely soft and very uniform. It is about No. 20 B.W.G., and its breaking weight, tested in the ordinary way, is about 45 lbs. This wire has been hung up in lengths of about 20 ft., and broken by weights applied, the breaking being performed more or less slowly.

"In the first place some experiments have been tried as to the smallest weight which, applied very cautiously and with precautions against letting the weight run down with sensible velocity, will break the wire.

These experiments have not yet been very satisfactorily carried out, but it is intended to complete them.

"The other experiments have been carried out in the following way: It was found that a weight of 28 lbs. does not give permanent elongation to the wire taken as it was supplied by the wire drawer. Each length of the wire, therefore, as soon as it was hung up for experiment, was weighted with 28 lbs., and this weight was left hanging on the wire for 24 hours.

Weights were then added till the wire broke, measurements as to elongation being taken at the same time. A large number of wires were broken with equal additions of weight, a pound at a time, at intervals of from three to five minutes--care being taken in all cases, however, not to add fresh weight if the wire could be seen to be running down under the effect of the weight last added. Some were broken with weights added at the rate of 1 lb. per day, some with 3/4 lb. per day, and some with 1/2 lb. per day. One experiment was commenced in which it was intended to break the wire at a very much slower rate than any of these.

It was carried on for some months, but the wire unfortunately rusted, and broke at a place which was seen to be very much eaten away by rust, and with a very low breaking weight. A fresh wire has been suspended, and is now being tested. It has been painted with oil, and has now been under experiment for several months.

"The following tables will show the general results of these experiments. It will be seen, in the first place, that the prolonged application of stress has a very remarkable effect in increasing the strength of soft iron wire. Comparing the breaking weights for the wire quickly broken with those for the same wire slowly broken, it will be seen that in the latter case the strength of the wire is from two to ten per cent. higher than in the former, and is on the average about five or six per cent. higher. The result as to elongation is even more remarkable, and was certainly more unexpected. It will be seen from the tables that, in the case of the wire quickly drawn out, the elongation is on the average more than three times as great as in the case of the wire drawn out slowly. There are two wires for which the breaking weights and elongations are given in the tables, both of them 'bright'

wires, which showed this difference very remarkably. They broke without showing any special peculiarity as to breaking weight, and without known difference as to treatment, except in the time during which the application of the breaking weight was made. One of them broke with 44-1/4 lbs., the experiment lasting one hour and a half; the other with 47 lbs., the time occupied in applying the weight being 39 days. The former was drawn out by 28.5 per cent. on its original length, the latter by only 4.79 per cent.

"It is found during the breaking of these wires that the wire becomes alternately more yielding and less yielding to stress applied. Thus from weights applied gradually between 28 lbs. and 31 lbs. or 32 lbs., there is very little yielding, and very little elongation of the wire. For equal additions of weight between 33 lbs. and about 37 lbs. the elongation is very great. After 37 lbs. have been put on, the wire seems to get stiff again, till a weight of about 40 lbs. has been applied.

Then there is a rapid running down till 45 lbs. has been reached. The wire then becomes stiff again, and often remains so till it breaks. It is evident that this subject requires careful investigation."

TABLES SHOWING THE BREAKING OF SOFT IRON WIRES AT DIFFERENT SPEEDS.

I.--WIRE QUICKLY BROKEN.

+------------------------+-----------+---------------+ | | Breaking | Per cent. of | | Rate of adding weight. | weight in | elongation on | | | pounds. | original | | | | length. | +------------------------+-----------+---------------+ | _Dark Wire._[29] | | | | 0-1/4 lb. per minute | 45 | 25.4 | | 1 " 5 minutes | 45-1/4 | 25.9 | | " 5 " | 45-1/4 | 24.9 | | " 4 " | 44-1/4 | 24.58 | | " 3 " | 44-1/4 | 24.88 | | " 3 " | 45-1/4 | 29.58 | | " 5 " | 44-1/4 | 27.78 | | _Bright Wire._[29] | | | | 1 lb. per 5 minutes | 44-1/4 | 28.5 | | " 5 " | 44-1/4 | 27.0 | | " 4 " | 44-1/4 | 27.1 | +------------------------+-----------+---------------+

[29] The wire used was all of the same quality and gauge, but the "dark" and "bright" wire had gone through slightly different processes for the purpose of annealing.

II.--WIRE SLOWLY BROKEN.

+--------------------+------------+--------------------+ | Weight added and | Breaking | Per cent. of | | number of | weight in | elongation on | | experiment. | pounds. | original length. | +--------------------+------------+--------------------+ | 1. 1 lb. per day | 48 | 7.58 | | 2. " " | 46 | 8.13 | | 3. " " | 47 | 7.05 | | 4. " " | 47 | 6.51 | | 5. " " | 47 | 8.62 | | 6. " " | 47 | 5.17 | | 7. " " | 46 | 5.50 | | 8. " " | 47 | 6.92 bright wire | | 1. 3/4 lb. per day | 49 | 8.50 | | 2. " " | 48-1/4 | 8.81 | | 3. " " | Broken by accident. | | 4. " " | 46 | 7.55 | | 5. " " | 46 | 6.41 | | 6. " " | 45-1/2 | 6.62 | | 1. 1/2 lb. per day | 48 | 8.26 | | 2. " " | 50 | 8.42 | | 3. " " | 49 | 7.18 | | 4. " " | 47 | 4.79} | | 5. " " | 46-1/2 | 6.00} bright wires | +--------------------+------------+--------------------+

The American Standard diameters of solid drawn or seamless bra.s.s and copper tube are as in the following table.

+----------+-----------------+---------------+---------------+ | Outside |Thickness Stubs's| Weight per | Weight per | |diameter. | wire-gauge. | running foot. | running foot. | | | | Bra.s.s tubes. | Copper tubes. | +----------+-----------------+---------------+---------------+ | 5/8 | 18 | 3/8 | 3/8 | | 3/4 | 17 | 1/2 | 1/2 | | 13/16 | 17 | 9/16 | 9/16 | | 7/8 | 17 | 5/8 | 5/8 | | 15/16 | 16 | 11/16 | 11/16 | | 1 | 16 | 3/4 | 3/4 | | 1-1/8 | 16 | 7/8 | 7/8 | | 1-1/4 | 12 and 14 | 1-1/4 | 1-1/4 | | 1-3/8 | 12 " 14 | 1-3/8 | 1-3/8 | | 1-1/2 | 12 " 14 | 1-1/2 | 1-6/10 | | 1-5/8 | 12 " 14 | 1-5/8 | 1-7/10 | | 1-3/4 | 12 " 14 | 1-3/4 | 1-8/10 | | 1-13/16 | 12 " 14 | 1-13/16 | 1-9/10 | | 1-7/8 | 12 " 14 | 1-7/8 | 1-15/16 | | 1-15/16 | 12 " 14 | 2 | 2-1/10 | | 2 | 12 " 14 | 2-1/8 | 2-1/4 | | 2-1/8 | 12 " 14 | 2-1/4 | 2-3/8 | | 2-1/4 | 12 " 14 | 2-3/8 | 2-1/3 | | 2-3/8 | 12 " 14 | 2-1/2 | 2-2/3 | | 2-1/2 | 11 " 13 | 2-3/4 | 3 | | 2-5/8 | 11 " 13 | 3 | 3-1/8 | | 2-3/4 | 11 " 13 | 3-1/8 | 3-1/4 | | 2-7/8 | 11 " 13 | 3-1/4 | 3-3/8 | | 3 | 11 " 13 | 3-3/8 | 3-1/2 | | 3-1/8 | 11 " 13 | 3-1/2 | 3-3/4 | | 3-1/4 | 11 " 13 | 3-7/8 | 4-1/8 | | 3-3/8 | 11 " 13 | 4-1/8 | 4-1/4 | | 3-1/2 | 11 " 13 | 4-1/4 | 4-3/8 | | 4 | 11 " 13 | 5 | 5-1/4 | | 4-1/4 | 11 " 13 | 6 | 6-1/2 | | 5 | 10 " 12 | 7 | 8 | | 6 | 10 " 12 | 9 | 10 | +----------+-----------------+---------------+---------------+

CHAPTER XVI.--SHAPING AND PLANING MACHINES.

The office of the shaping machine is to dress or cut to shape such surfaces as can be most conveniently cut by a tool moving across the work in a straight line.

The positions occupied among machine tools at the present time by shaping and planing machines are not as important as was the case a few years ago, because of the advent of the milling machine, which requires less skill to operate, and produces superior work.

All the cutting tools used upon shaping and planing machines have already been described with reference to outside tools for lathe work, and it may be remarked that a great deal of the chucking done on the shaping and planing machine corresponds to face plate chucking in the lathe. Both shaping machines and small planing machines, however, are provided with special chucks and work-holding appliances that are not used in lathe work, and these will be treated of presently. On large planing machines chucks are rarely used, on account of the work being too large to be held in a chuck. Shaping machines are also known as shapers and planing machines as planers.

[Ill.u.s.tration: Fig. 1496.]

The simplest form of shaping machine, or shaper as it is usually termed in the United States, is that in which a tool-carrying slide is reciprocated across the work, the latter moving at the end of each back stroke so that on the next stroke the tool may be fed to its cut on the work. Fig. 1496 represents a shaper of this kind constructed by Messrs.

Hewes and Phillips, of Newark, New Jersey, in which P is a cone pulley receiving motion from a countershaft, and driving a pinion which revolves the gear-wheel Q, whose shaft has journal bearing in the frame of the machine. This shaft drives a bevel pinion gearing with a bevel-wheel in one piece with the eccentric spur-wheel S, which is upon a shaft having at its lower end the bevel-wheel B to operate the work-feeding mechanism. S drives an eccentric gear wheel R, fast upon the upper face of which is a projection E, in which is a [T]-shaped groove to receive and secure a wrist or crank pin which drives a connecting rod secured to the slide A by means of a bolt pa.s.sing through A, and secured to the same by a nut D.

When the gear-wheel R revolves, the connecting rod causes slide A to traverse to and fro endways in a guideway, provided on the top of the frame at X. On the end of this slide is a head carrying a cutting tool T, which, therefore, moves across the work, the latter being held in the vise V, which is fast upon a table W upon a carriage saddle or slider _p_, which is upon a horizontal slide that in turn fits to a slide vertical upon the front of the machine, and may be raised or lowered thereon by means of an elevating screw driven by a pair of mitre-wheels at F. The slider and table W (and therefore the vise and the work) are moved along the horizontal slide to feed the work to the tool cut as follows. A short horizontal shaft (driven by the bevel pinions at B), drives at its outer end a piece C, having a slot to receive a crank pin driving the feed rod N, which operates a pawl K engaging a ratchet wheel which is fast upon the horizontal screw that operates slider _p_.

[Ill.u.s.tration: Fig. 1497.]

The diameters of the eccentric gear-wheels E and S are equal; hence, C makes a revolution and the cross feed is actuated once for every cutting stroke. The swivel head H is bolted to the end of the slide or ram, as it is sometimes called, A, and is provided with a slide I upon which is a slider J, carrying an ap.r.o.n containing the tool post holding the cutting tool, the construction of this part of the mechanism being more fully shown in Fig. 1497. The eccentric gear-wheels R S are so geared that the motion of the slide A during the cutting stroke (which is in the direction of the arrow) is slower than the return stroke, which on account of being accelerated is termed a quick return. Various mechanisms for obtaining a quick return motion are employed, the object being to increase the number of cutting strokes in a given time, without accelerating the cutting speed of the tool, and some of these mechanisms will be given hereafter.

[Ill.u.s.tration: Fig. 1498.]

Referring again to the mechanism for carrying the cutting tool and actuating it to regulate the depth of cut in Fig. 1497, G is the end of the slide a to which the swivel head H is bolted by the bolts _a_ _b_.

The heads of these bolts pa.s.s into [T]-shaped annular grooves in G, so that H may be set to have its slides at any required angle. I is a slider actuated on the slide by means of the vertical feed screw which has journal bearing in the top of H, and pa.s.ses through a nut provided in I. To I is fastened the ap.r.o.n swivel J, being held by a central bolt not seen in the cut, and also by the bolt at _c_. In J is a slot, which when _c_ is loosened permits J to be swung at an angle. The ap.r.o.n K is pivoted by a taper pin L, which fits into both J and K. During the cutting stroke the ap.r.o.n K beds down upon J, but during the back stroke the tool may lift the ap.r.o.n K swinging upon the pivot L. This prevents the cutting edge of the tool from rubbing against the work during the return stroke.

Thus in Fig. 1498 is a piece of work, and it is supposed that a cut is being carried down the vertical face or shoulder at A; by setting the ap.r.o.n swivel at an angle and lifting the tool during the return stroke, its end will move away from the face of the shoulder. The slider I obviously moves in a vertical line upon slides M.

[Ill.u.s.tration: Fig. 1499.]

To take up the wear of the sliding bar A, various forms of guideways and guides are employed, a common form being shown in Fig. 1499. There are two gibs, one on each side of the bar, and these gibs are set up by screws to adjust the fit. In some cases only one gib is used, and in that event the wear causes the slide to move to one side, but as the wear proceeds exceedingly slowly in consequence of the long bearing surface of the bar in its guides, this is of but little practical moment. On the other hand, when two gibs are used great care must be taken to so adjust the screws that the slide bar is maintained in a line at a right angle to the jaws of the work-holding vice, so that the tool will cut the vertical surfaces or side faces of the work at a right angle to the work surface that is gripped by the vice.

To enable the length of stroke of slide A, Fig. 1496, to be varied to suit the length of the work, and thus not lose time by uselessly traversing that slide, E is provided with a [T]-slot as before stated, and the distance of the wrist pin (in this slot) from the centre of wheel E determines the amount of motion imparted to the connecting rod, and therefore to slide A. The wrist pin is set so as to give to A a rather longer stroke than the work requires, so that this tool may pa.s.s clear of the work on the forward stroke, and an inch or so past the work on the return stroke, the latter giving time to feed the tool down before it meets the work.

The length of the stroke being set, the crank piece E (for its slot and wrist pin correspond to a crank) is, by pulling round the pulley P, brought to the end of a stroke, the connecting rod being in line with slide A. The nut D is then loosened and slide A may then be moved by hand in its slideway until the tool clears the work at the end corresponding to the connecting rod position when nut D is tightened and the stroke is set.

[Ill.u.s.tration: Fig. 1500.]

Now suppose it is required to shape or surface the faces _f_ and _f'_, the round curve S and the hollow curve C of the piece of work shown held in a vice chuck in Fig. 1500, and during the cutting stroke the slide _a_ will travel in the direction of _n_ in the figure, while during its return stroke it will traverse back in the direction of _i_. The sliding table W in Fig. 1496 would continuously but gradually be fed or moved (so much per tool traverse, and by the feeding mechanism described with reference to Fig. 1501) carrying with it the vice chuck, and therefore the work. When this feeding brought the surface of curve S, Fig. 1500, into contact with the tool, the feed screw handle in figure would be operated by hand so much per feed traverse, thus raising the slider, and therefore the tool, in the direction of _l_, and motion of the work to the right and the left of the tool (by means of the feed handle) would (if the amount of tool lift per tool stroke is properly proportioned to the amount of work feed to the right) cause the tool to cut the work to the required curvature. When the work had traversed until the tool had arrived at the top of curve S, the direction of motion of the feed-screw handle Z in Fig. 1496 must be reversed, the tool being fed down so much per tool traverse (in the direction of _m_) so as to cut out the curves from the top of S to the bottom of _c_, the face _f'_ being shaped by the automatic feed motion only.

The feed obviously occurs once for each cutting stroke of the tool and for the vertical motion of the tool, or when the tool is operated by the hand feed-screw handle in Fig. 1496, the handle motion, and therefore the feed should occur at the end of the back stroke and before the tool again meets the work, so as to prevent the cutting edge of the tool from sc.r.a.ping against the work during its back traverse.

In this connection it may be remarked that by setting the ap.r.o.n swivel over, as in Fig. 1498, the tool is relieved from rubbing on the back stroke for two reasons, the first having been already explained, and the second being that to whatever amount the tool may spring, bend, or deflect during the cutting stroke (from the pressure of the cut), it will dip into the work surface and cut deeper; hence on the back stroke it will naturally clear the surface, providing that the next cut is not put on until the tool has pa.s.sed back and is clear of the work.

[Ill.u.s.tration: Fig. 1501.]

Referring now to the automatic feed of the sliding table W, in Fig.

1496, the principle of its construction may be explained with reference to Fig. 1501, which may be taken to represent a cla.s.s of such feeding mechanisms. A is a wheel corresponding to the wheel marked M in Fig.

1496, or, it may be an independent wheel in gear with the feed wheel. On the same shaft as A is pivoted an arm B having a slot S at one end to receive a pin to which the feed rod E may connect. F is a disk rotated from the driving mechanism of the shaping machine, and having a [T]-shaped slot G G, in which is secured a pin to actuate the rod E. As F rotates E is vibrated to and fro and the catch C on one stroke falls into the notches or teeth in A and causes it to partly rotate, while on the return stroke of E it lifts over the teeth, leaving A stationary.

The amount of motion of B, and therefore the quant.i.ty of the feed, may be regulated at either end of E; as, for example, the farther the pin from the centre of G the longer the stroke of E, or the nearer the pin in S is to the centre of B the longer the stroke, but usually this provision is made at one end only of E.

To stop the feed motion from actuating, the catch C may be lifted to stand vertically, as shown in dotted lines in position 2, and to actuate the feed traverse in an opposite direction, C may be swung over so as to occupy the position marked 3, and to prevent it moving out of either position in which it may be set a small spring is usually employed.

Now suppose that the tool-carrying slide A, Fig. 1496, is traversing forward and the tool will be moving across the work on the cutting stroke, as denoted by the arrow _k_ in Fig. 1502, the line of tool motion for that stroke being as denoted by the line _c_ _a_. At _a_ is the point where the tool will begin its return stroke, and if the work is moved by the feeding mechanism in the direction of arrow _e_, then the line of motion during the return stroke will be in the direction of the dotted line _a_ _b_, and as a result the tool will rub against the side of the cut.

[Ill.u.s.tration: Fig. 1502.]

It is to obviate the friction this would cause to the tool edge, and the dulling thereto that would ensue, that the pivot pin L for the ap.r.o.n is employed as shown in Fig. 1497, this pin permitting the ap.r.o.n to lift and causing the tool to bear against the cut with only such force as the weight of the ap.r.o.n and of the tool may cause. Now suppose that in Fig.

1503 we have a piece of work whose edge A A stands parallel to the line of forward tool motion, there being no feed either to the tool or the work, and if the tool be set to the corner _f_ its line of motion during a stroke will be represented by the line _f_ _g_. Suppose that on the next stroke the feed motion is put into action and that feeding takes place during the forward stroke, and the amount of the feed per stroke being the distance from _g_ to _h_, then the dotted line from _f_ to _h_ represents the line of cut. On the return stroke the line of tool motion will be from _h_ along the dotted line _h_ _k_, and the tool will rest against the cut as before. Suppose again that the feed is put on during the return stroke, and that _c_ _c'_ represents the line of tool motion during a cutting stroke, and the return stroke will then be along the line from _c'_ to _b_, from _c_ to _b_ representing the amount of feed per stroke; hence, it is made apparent that the tool will rub against the cut whether the feed is put on during the cutting or during the return stroke. Obviously then it would be preferable to feed the work between the period that occurs after the tool has left the work surface on the return stroke and before it meets it again on the next cutting stroke. It is to be observed, however, that by placing the pin actuating the rod E, Fig. 1501, on the other side of the centre of the slot G in F, the motion of E will be reversed with relation to the motion J of the slide; hence, with the work feeding in either direction, the feed may be made to occur during either the cutting or return stroke at will by locating the driving pin on the requisite side of the centre of G.

[Ill.u.s.tration: Fig. 1503.]

An arrangement by Professor Sweet, whereby the feed may be actuated during the cutting or return stroke (as may be determined in designing the machine), no matter in which direction the work table is being fed, is shown in Fig. 1504. Here there are two gears A and D, and the pawl or catch C may be moved on its pivoted end so as to engage either with A or D to feed in the required direction.