Fig. 577Fig. 577.
Fig. 577.
Fig. 578Fig. 578.
Fig. 578.
An excellent example of an elevating rest for a weighted lathe is shown inFigs. 577and578, which represent the construction in the Pratt and Whitney lathe.ais the lathe shears upon which slides the carriage provided withVslidewaysrfor the sliding pieceb, and provided at the other end with the guidesh. The cross slidesis pivoted uponbatd, and fits at the other end between the guidesh. Ateis the elevating screw which when operated raises or lowers that end of the elevating rest to adjust the tool height. This also affords an excellent means of making a minute adjustment for depth of tool cut. The tool restfis bolted tos.
The weightwis suspended fromsand, therefore, holds one end ofstob, the lathe toc, andctoa; at the other end the weight holdsstoc(through the medium of the elevating screwe) andctoa. The cross feed nutnis fast tos, the cross feed screw being operated by hand wheelg.bis provided with theVslidewaysr, which slide upon correspondingVslidesr′uponc;pis a lug cast uponc, andkis a screw threaded inb. When the end of screwkabuts againstpthe motion ofs, and, therefore, of the cutting toolt, towards the work is arrested, hence when the tool is adjusted to the proper depth of cut,kis operated to abut firmly againstp, and successive pieces may be turned to the same diameter without requiring each piece to be measured for diameter.nis the handle for opening and closing the nut for the feed screwq, andzis the wheel for the hand feed traverse. The length of cross feed motion is determined by the length of the crossVslidesr′.
This class of rest possesses the advantage that no lost motion in the slides occurs by reason of the wear, because the weight keeps the parts in constant contact notwithstanding such wear; on the other hand, however, the slideVs sustain the extra wear due to the weightwin addition to the weight of the carriage. Lathes of this class are intended for light work, and are less suited for boring than for plain turning; they are, however, very convenient, and are preferred by many to any other kind of lathe for short and light work.
Fig. 579Fig. 579.
Fig. 579.
Fig. 580Fig. 580.
Fig. 580.
The tool rest being removable may be supplanted by other special forms of rest. ThusFigs. 579and580represent a special rest for carrying two tools to cut pieces of work to the exact same length. Boltsdandeare to secure the restato the elevating rest, andc care the clamps for the two toolsb.
Largeimage(334 kB).Fig. 581Fig. 581.
Largeimage(334 kB).
Fig. 581.
Fig. 581represents a cross sectional view of the Putnam Tool Company’s gibbed elevating rest, there being a gib on the underneath side of the front shear. The elevating screw is pivoted by a ball joint. By employing a gib instead of a weight, the bed may be provided with cross girts or ribs joining the two sides of the shear, thus giving much greater stiffness to it.
Largeimage(107 kB).Fig. 582Fig. 582.
Largeimage(107 kB).
Fig. 582.
Largeimage(68 kB).Fig. 583Fig. 583.
Largeimage(68 kB).
Fig. 583.
Largeimage(106 kB).Fig. 584Fig. 584.
Largeimage(106 kB).
Fig. 584.
Figs. 582,583, and584represent a lathe feed motion by William Munzer, of New York. The object in this motion is to insure that no two feeds can be put into operation simultaneously, because putting the feed in motion in one direction throws it out of gear for either of the others. Another object is to have the transmitting motion as direct as possible so as to avoid the rotation of any wheels not actually necessary for the transmission of the motion; and a third object is to enable the throwing out of gear of all wheels (when no feed motion at all is required) without leaving the apron.
The means employed to effect these objects are asfollows:—
InFig. 582frepresents the independent feed spindle andsthe lead-screw:fis splined to drivea,a′anda′′, which is a sleeve in one piece, and consists of a circular rack ata, a bevel pinion ata′, and a second bevel pinion ata′′. This sleeve may be operated in either direction alongfby rotating the pinionb. As shown in the cuta′anda′′are both out of gear with the bevel-wheelc, but ifbbe rotated to the right thena′will be in gear withc, or if it be operated to the left thena′′will be in gear withc. Now the direction of rotation ofcwill be governed by which pinion,a′ora′′, drives it, and these are the means by which the direction of the feed traverse and also of the cross feed is determined.
If none of the feeds are required to operate, the sleeve occupies the position shown in the cut, and the circular rack atasimply rotates whileband all other parts remain at rest. On the same central pin ascis the pinionddriving a spur geare′′. On the same centre pin aseis the gearfdrivingg, which is on the same central pin ascandd. The gearhis fixed to and rotates withgand drivesi; all these gears serving to reduce the speed of motion when operating to feed the carriage traverse in either direction.
A gearjis carried on the end of a leverk, being pivoted atl. In the position shownjis out of gear with all gears, but it may be swung to the right so as to engage with wheeliand wheelm, and convey the motion ofitom. Upon the same spindle asmis the pinionn, engaging with the racko, which is fast on the lathe bed. This completes the automatic feed traverse.
For a hand feed traverse, pinionpis employed to drivem, which is fast ton. The cross feed is self-acted by moving leverkto the left, causing it to engage with pinionqas well as witht,qbeing fast on the cross feed screw. To lockjin either of its three positions there is provided on leverka spring locking pinr, shown clearly inFig. 584, which represents an irregular section of the gearing viewed from the headstock of the lathe. The pinris pressed inward by the spiral spring shown, and has a conical end fitting into holes provided in the apron to receive it. There are three of these holes, shown in dotted lines ata b cinFig. 582. When the pin is inathe leverk, and therefore wheelj,Fig. 582, is locked out of gear; when it is in holebwheeljis locked in gear withiandm, and when it is incthe wheeljis in gear withtandq, and the cross feed is actuated.
A similar locking device is provided for the pinionbfor actuatinga; thus inFig. 582bis the lever, the spring pin being atr′′; or referring toFig. 584,xis the lever fast atxon the pin drivingb, andr′is the spring pin.
The nut for the lead screw is secured either in or out of gear with the screw in the same manner,x′,Fig. 583, being the lever andr′′the spring pin.
Fig. 585Fig. 585.
Fig. 585.
In screw cutting the cutting tool requires to be withdrawn from the thread while the carriage traverses back, and it is somewhat difficult to know just how far to move the tool in again in order to put on a proper depth of cut. To facilitate this the device shown inFig. 585(which is taken from the “American Machinist,”) is sometimes employed.
It consists of a ringcinserted between the cross slidedand the handle hubbhaving journal bearing on and rotating with the latter. When the first cut is put on, the mark oncis coincident with that ond, and the ring is then, while the first cut is traversing, moved (supposing the cross feed screw to have a right-hand thread) to the left, as shown in the figure, to the amount the handle will be required to move to the right to put on the nextcut, and when the next cut is put on the handle will be moved the distance it was moved to withdraw the tool for the back traverse, and in addition enough to make the marks coincide, then while the second cut is being taken the ring is again moved to the left, as in the cut, to give the depth of cut for the next traverse, and so on.
If the cross feed screw has a left-hand thread, the mark on the ring would require to be moved to the right instead of to the left of the mark ond. It is obvious that this answers the same purpose, but is more exact than the chalk mark before referred to, and, indeed, that chalk mark could be used in the same way, leaving the chalk markdand rubbing out that oncwhile the cut is proceeding and making a new one for the next cut.
Fig. 586Fig. 586.
Fig. 586.
Another device for use on lathes specially designed for screw-cutting is shown inFig. 586, in whicharepresents the cross feed screw. It is fast to the notched wheelb, and is operated by it in the usual way.cis a short screw which provides journal bearing for the screwaby a plain hole. It is screwed on the outside, and the plate in which it fits acts as its nut. It is fast to the handled, and is in fact operated by it. The handle or lever is provided with a catche, pivoted in the enclosed boxf, which also contains a means of detaining the catch in the notches of the wheel, or of holding it free from the same when it is placed clear. If, then, the leverdbe moved back and forth the feed screwa, and hence the slide rest, will be operated; while, if the catch be placed in one of the notches on the wheelb, both the screws,aandc, will act to operate the rests. When, therefore, the tool is set to touch the diameter of the work, the catcheis lifted and the feed wheelbrotated, putting on the cut until the catchewill fall into the next notch inb, the leverdresting in the meantime on the studg. When the cut is carried along the work to the required distance the tool is withdrawn by movingdover until it rests upon stud or stoph. While the slide rest is traversing backeis lifted andbrotated so thatewill fall into the next notch, and when the tool starts forward againdis moved over fromhtog, as shown in the figure, and the tool cut is put on.
When the device is not required to be usedeis thrown out,drests one, and the feed is operated in the ordinary manner.
Fig. 587Fig. 587.
Fig. 587.
A simple attachment for regulating on a slide rest the depth of tool cut in screw cutting or for adjusting the cut to a requisite diameter when a number of pieces are to be turned to diameterby a finishing cut, is shown inFig. 587, in whichbrepresents the slide rest carriage, andethe cross slide on which the slide restais traversed by means of the cross feed screwf. A screw is screwed into the rest, as shown, carrying the two circular milled edge nutsr p; the screw passes an easy fit through the piecec, which is capable of being fixed in any position along the slideeby means of the set screws; the nutris set in such a position on the screw that it will abut againstcwhen the tool is clear of the work surface (for the back traverse) whilepmay be used in two ways:—First it may be set so that when it comes againstcthe thread is cut to the required depth, and thus act as stop to give the thread depth without trying the gauge: or it may be used to answer the same purpose and in the same way as the ringcinFig. 585.
The use of this device as a stop to gauge the thread depth is confined to such lengths of work as enable the tool to cut several pieces without requiring regrinding, because when the tool is removed to grind it, it is impracticable to set it exactly the same distance out from the tool post, hence the adjustment ofpbecomes destroyed. It is better, therefore, in most cases where a number of threads of equal pitch and diameter are to be cut, to rough them all out, cutting the threads a little above the gauge diameter so as to leave a finishing cut to be taken. In roughing out, however, the nutpmay still be used to regulate the depth.
For the finishing cut the tool may be ground andpadjusted to give the requisite depth of cut, taking a single traverse over each thread to finish it. This, of course, preserves the tool and enables it to finish a larger number of threads without regrinding, and the consequent readjustment ofp.
It is obvious that the nutpmay be employed in the same manner to turn a number of plain pieces to an equal diameter.
Fig. 588Fig. 588.
Fig. 588.
It is preferable in a device of this kind, however, to employ the two adjusting nutspandqinFig. 588,qbeing a clamp nut that can be closed by a screw so as to firmly grip the threaded stud.qis adjusted so that whenpabuts against it the tool will cut to the correct diameter when it is moved in as far as nutsp qwill permit. The use of the second nutpis as follows:—Suppose a first cut has been taken andpmay be screwed up to just meet the face of clampc. Then while the carriage is traversing,pmay be screwed back towardsqsufficiently to put on the next cut, and so on, so thatpis used to adjust the depths of the roughing, andqthat of the finishing cut.
Sometimes a feed motion to a slide rest is improvised by what is known as thestar feed, the principle of action of which is as follows: Upon the outer end of the feed screw of the boring bar or slide rest, as the case may be, is fastened a piece of iron plate, which, from having the form in which stars are usually represented, is called the star. If the feed is for a slide rest a pin is fastened to the lathe face plate or other revolving part, in such a position that during the portion of the revolution in which it passes the star it will strike one of the star wings, and move it around sufficiently to bring the next wing into position to be struck by the pin during its succeeding revolution. When the feed is applied to a revolving boring bar the construction is the same, but in this case the pin is stationary and the star revolves with the feed screw of the bar.
Fig. 589Fig. 589.
Fig. 589.
InFig. 589is shown a star feed applied to a slide rest.ais the slide rest, upon the end of the feed screw of which the star,b, is fitted.cis a pin attached to the face plate of the lathe, which, as it revolves, strikes one of the star wings, causing it to partly rotate, and thus move the feed screw. The amount of rotation of the feed screw will depend upon the size of the star and how far the circle described by the pincintersects the circle described by the extreme points of the star wings. Thus the circles denoted byd eshow the path of the pinc; the circlef hthe path of the star points, and the distance fromftogthe amount which one intersects the other. It follows that at each revolution ofcan arm or wing of the star will be carried from the pointgto pointf, which, in this case, is a sixth of a revolution. If more feed is required, we may move the pinc, so that it may describe a smaller circle thand e, and cause it to intersectf hto a greater extent, in which case it will move the star through a greater portion of its revolution, striking every other wing and doubling the amount of feed.
It will be observed that the pointsfandgare both below the horizontal level of the slide rest’s feed screw, and therefore that the sliding motion of the pincupon the face of the star wings will be from the centre towards the points. This is better, because the motion is easier and involves less friction than would be the case if the pin contact first approached and then receded from the centre, a remark which applies equally to all forms of gearing, for a star feed is only a form of gearing in which the star represents a tooth wheel, and the pin a tooth in a wheel or a rack, according to whether its line of motion is a circle or a straight line.
It is obvious that in designing a star feed, the pitch of the feed screw is of primary importance. Suppose, for example, that the pitch of a slide rest feed screw is 4 to an inch, and we require to feed the tool an inch to every 24 lathe revolutions; then the star must have 6 wings, because each revolution of the screw will move the rest1⁄6in., while each revolution of the pincwill move the star1⁄6of a revolution, and 4 × 6 = 24. To obtain a very coarse feed the star attachment would require to have two multiplying cogs placed between it and the feed screw, the smaller of the cogs being placed upon the feed screw.
Fig. 590Fig. 590.
Fig. 590.
In many lathes of European design, the feeds or some of them,are actuated by ratchet handles, operated by an overhead shaft, having arms which rock back and forth. Thus inFig. 590is a lathe on which there is provided atacrank disc, carrying in a dovetail slot a pinp, for rocking the overhead shaft from whose arms a chain is attached which may be connected to the ratchet handle shown on the cross-feed screw, the weight being for the purpose of carrying that handle down while the chain pulls it up. To regulate the amount of feed the pinpis adjusted in the slot ina, or the chain may be attached in different positions along the length of the ratchet arm, the weight being provided with a set screw so that it may be set in any required position along the ratchet arm.
Tool-holding Devices.—Perhaps no part of a lathe is found in American practice with so many different forms of construction as the device for holding the cutting tool. The requirements for a lathe to be used on light work and where frequent changes in the position of the tool are necessary, are quite different from those for a lathe intended to take as heavy a cut as the lathe will properly drive, and wherein tools having the cutting edge at times standing a long way out from the tool post (as sometimes occurs in the use of boring tools). In the former case a single holding screw will suffice, possessing the advantage that the tool may be quickly inserted, adjusted for height and set to one side or the other, with a range of motion which often permits of a tool that has taken a parallel cut being moved in position to capacitate it to take a facing one, which would not be the case were its capacity for side adjustment limited.
In the case of the common American lathe having a self-acting feed and no compound rest, the tool post is usually employed, the rest being provided with aTslot such as shown inFig. 577. This enables the tool post to be moved from side to side of the tool rest, and swing around in any required position. In connection with such tool posts various contrivances are employed to enable the height of the cutting edge of the tool to be readily adjusted. Thus in theFig. 591, the tool post is surrounded by a cupped washerw, and through the slot in the tool post passes a gibg, which may be moved endways in the slot and thus elevates or depresses the tool point.
The objection to this is that the tool is not lifted parallel, or in other words is caused to stand out of its proper horizontal position which alters the clearance of the tool, and by presenting the angles forming the tool edge in an improper position, with relation to the work, impair its cutting qualification, as will be shown hereafter when treating of lathe cutting tools.
An improvement on this form has been pointed out by Professor John E. Sweet, whose device is shown inFig. 592. Here the washer or ring is rounded and the bottom surface of the gib is hollowed, so that chips or dirt will to a great extent fall off, and every time the tool post is swung the gib acts to push off whatever dirt may lodge on the washer.
In the design shown inFig. 593, the tool rests upon two washerswthat are tapered, and its height is adjusted by revolving one of these washers, it being obvious that the limit of action to depress the tool point is obtained when the two thin sides of the washers are placed together, and on the same side of the tool post as the cutting edge of the tool, while the limit of action to raise the tool point is obtained when the washers have their thick sides together and nearest to the tool point.
Here again the tool is thrown out of level, and to obviate this difficulty the stepped washer shown inFig. 594may be used, the steps on opposite sides of the washer being of an equal height. This enables the tool to be raised or lowered without being set out of the horizontal position; but it has the defect that the adjustment cannot be made any finer than the height of the steps, and if the height is made to vary but slightly, in order to refine, as it were, the adjustment, the range of tool elevation or depression is correspondingly limited. Another form of stepped washer is shown inFig. 595, in which no two steps are of the same height. This affords a wider range of adjustment, because the same two steps will alter the height of the tool by simply turning the washer one-half revolution. It has two defects, however; first, the least amount of adjustment is that due to the difference in height of the steps; and, second, when the tool is elevated it grips the washer ata, so that the tool is not supported across the full width of face of the washer, as it should be.
A defect common to all devices in which the tool is thrown out of level, is that the binding screw does not bed fair upon the tool, and as a result it is apt, if screwed home very firmly, as is necessary to hold boring tools that stand far out from the tool post, to spread the screw end as inFig. 596, or to bend it.
A very convenient tool-adjusting device is shown inFig. 597. It consists of a threaded ringnreceiving the threaded bushm, the tool height being adjusted by screwing or unscrewing one within the other.
The objection to this is, that it occupies so much vertical height that there is not always room to admit it, which occurs, for example, in compound slide rests on small lathes.
On these rests, therefore, a single washer is more frequently used, which answers very well when the tool post is in a slot, so that it can be moved from side to side of the rest as occasion may require. When, however, the position of the tool post is fixed it has the disadvantage that the pointp,Fig. 598, where the tool takes its leverage, is too far removed, and the tool is therefore liable to bend or spring from the pressure of the cut.
InFig. 599is an elevating device sometimes used on the compound rests of large lathes. The top of the rest is provided with a hubh, threaded externally to receive a ring nutr, around whose edge there are numerous holes to receive a pin for operating the nut. The tool-post is situated central in the hub. When the tool is loose the ring nut can be operated by hand or the tool may be gripped lightly and the ring nut operated by a pin. The level of the tool is here maintained; it is supported to about the edge of the rest on account of the large diameter of the ring nut, and a very delicate adjustment for height can be made, but such a device is only suitable for large lathes on account of the depth of the ring nut and hub.
On small slide-rests the device shown inFig. 600is often found. It consists of a holderh, in which is cut a seat for the tool, this seat being inclined to give the piece of steel used as a tool a certain constant degree of angle, and at the same time to permit of the tool being moved endwise in the holder to set it for height; but, as the tool requires to be pushed farther and farther through the holder to raise it, it is not so well supported as is desirable when slight tools are used, unless the holder is made long, so as to pass through the tool post with the tool. Again, it does not support the tool sideways unless the tool steel is dressed up and closely fits the groove in the holder.
InFig. 601w ware two inverted wedges which afford an accurate adjustment, but the range is limited, because if the wedges have much taper they are apt to move endways when the tool is fastened.
A convenient device for the compound rests of small lathes is shown inFig. 602. It consists of a holder pivoted upon a central post and carrying two tool-binding screws, hence it can be revolved to set the tool in any required position. A similar device is shown inFig. 603, in which the central post is slotted atato receive the tool, and also carries a platec, held by the nutn, and provided with tool-holding screwsbandb′, which abut against the top of the rest, a top view of the device being shown inFig. 604. Platecmay thus be swung around to set the tool in any required position on either side of the rest.
In Maudslay’s slide rest, the tool clamp shown inFig. 605is employed. Screwsaare employed to grip the tool moderately firm, and a turn of screwsb(whose ends abut against the top of the slide rest) very firmly secures the tool, since it moves the clampcas a lever, whose fulcrum is the screwa.
Fig. 607Fig. 607.
Fig. 607.
Figs. 606and607represent the Whitworth tool clamp, the clamping plates of which change about upon the four studs, and are supported at their inner ends by a block equal in height to the height of the tool steel.
Fig. 608Fig. 608.
Fig. 608.
Fig. 609Fig. 609.
Fig. 609.
Fig. 610Fig. 610.
Fig. 610.
Fig. 611Fig. 611.
Fig. 611.
Figs. 608,609,610, and611represent the “Lipe” tool post, so called from the name of its inventor. The top of the cross slide is cylindrical, and is bored to receive the tool post which has a cylindrical stem. The cylindrical part of the tool post is split vertically, and has two lips, the boltdpassing through one lip and threading into the other, so that by operating boltdthe tool post may be gripped very firmly or released, so that it may be revolved to bring the tool into any required position after it is fastened in the tool post, which is a great advantage because the tool is brought to a solid seating in the post before its height is adjusted, and will not therefore be altered in height by setting up the set screws as often occurs in ordinary tool posts. From the shape of the tool post, the tool may be gripped by one set screw only, when required for light duty, or by two set screws for heavy duty or for boring, while in either case it is supported clear to the edge of the rest.
Fig. 608shows the tool in position, held by a single screw, for work requiring the tool to be close up to the work driver. InFig. 609a tool is shown held as is required by work between centres, but both set-screws are used.Fig. 610shows a tool in position for boring, two set-screws being used.Fig. 611shows a tool being held for the same purpose, but by a single screw, and it will be observed that the advantage of the second set-screw is obtained without in any way sacrificing the handiness of the post, when used with a single screw. Whether one or two set-screws are used, the boring tool may be forged from a single bar of octagon steel, which can be seated in a piece like that shown ateinFig. 610, which is grooved so as to receive and hold the tool. As is well known, boring tools are the most troublesome both to forge and to adjust in the lathe, and, as the result, a light tool is often used because no other is at hand and it is costly to make a new one. When, however, the tool can be forged from a plain piece of steel, these objections are overcome, and a sufficient number of tools may be had so that one can always be found suitable for any ordinary sized hole, the object being to use as rigid a tool as can be got into the hole bored.The feature of maintaining the tool level is of great importance in boring work, because when the tool requires to be set out of level to adjust its height, it will generally strike against the mouth of the hole if the latter is of much depth. This annoyance is also frequently met with in boring tools which are forged out of rectangular steel, because the rounded stem is generally left taper. The largest end of the taper is generally nearest the tool post. Hence the capacity to use octagon steel and keep it level while adjusting its height, added to the fact that the tool is supported clear to the edge of the tool rest, and the tool post is so blocked as to virtually become a part of the rest, constitute a very important advantage.
Fig. 612Fig. 612.
Fig. 612.
A common device on large lathes is shown inFig. 612, the two clamps being shown in position for outside turning, and being changed (so as to stand at a right angle to the position they occupy in the figure) for holding boring tools. The bolts are enveloped by spiral springs which support the clamps.
Fig. 613Fig. 613.
Fig. 613.
Figs. 613and614represent the tool holders employed in the Brown and Sharpe small screw machines. In the front rest,Fig. 613, the piecerreceives two adjusting and tool-gripping screwss, upon which sits the gibg, and upon this the tool is placed. The surfaceeat the top of the tool post slot is curved so that it will bear upon the top of the tool at a point only. The tool is here supported along the full length of the gib, and there is no set-screw at the top of the tool post, which enables a much more unobstructed view of the tool.