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ALL turners who have served their time on a light lathe the kind used by most amateurs up to a generation ago-know that a decisive factor in its successful use is unremitting care in grinding and setting tools. This enables you to get round many of the problems caused by the light construction and lack of refinements. Contrariwise, without unrelaxing attention to tools, you are soon in trouble with rough finishes or wavy surfaces on the work. A production centre lathe has a broad bed, a spindle with widely spaced bearings, and a range of feeds for the saddle. Straightforward work can be done on it with much less skill and attention than is needed for the same job on a smaller and lighter lathe of the sort that many of us normally use.

 

 

On the smaller machine, spindle and slides must be in good adjustment; and you may have to feed the saddle by hand from the leadscrew, there being no fine self-acting feed to give an overlapping cut with almost any round-nosed tool. To get a fine finish, you may have to hone a small flat on the cutting edge of the tool, and then watch the depth of cut and the rate of feed to avoid chatter. A good general-purpose turning tool is shown at diagram A, with the essential angles and clearances. These comprise two rake angles, top rake V and side rake W, and three clearance angles, top clearance Y, front clearance X and side clearance Z. The front rake V and the front clearance X permit the tool to cut freely when it is pushed straight to the work by the cross-slide feed. The side-rake W and the side-clearance Z do the same when the tool is fed sideways by e th topslide feed or the leadscrew. The top-clearance Y reduces the length of cutting edge which is in contact with the work during a sideways cut. If this were not done, the wide contact would induce chatter-particularly on a light lathe.

 

 

Grinding and Setting Tools

 

 

The angles are shown sharp to the square shank of the tool bit to emphasize them, although the shape of an actual tool is to the dotted lines. The tool bit is intended for mounting horizontally on a top-slide, or in a turret. When it is mounted at an angle in a tool holder, the grinding must allow for this. To begin grinding a tool bit, you can hold it as at Bl at an angle and above the centre on the periphery of a grinding wheel. This produces a curved surface on the end of the bit which you can flatten later on the side of the wheel. In this way, you reduce wear on the side which cannot be rectified so easily as the periphery by use of a dresser. Some of the other grinding can be done on this principle. The first grinding leaves the bit with the front clearance angle X and the top clearance angle Y. You grind the side clearance angle Z as at B2, on the side of the wheel with a twist in the direction of the arrow. The next step is to grind the two rake angles V and W. This you do as at Cl, holding the tool to the other side of the grinding wheel, at an angle, and again with a twist. Lastly, you grind the radius by swinging the tool as at C2. You can cool it in water between grindings, and finally polish its faces with an oilstone. Diagram Dl illustrates how the tool should be mounted with its cutting tip at centre height. Use packing as required-and if the tip is above centre, you can pack under the back end of the bit, although by so doing you alter the cutting angles. With an above-centre setting D2, contact may be below the tool edge; with a below-centre setting D3 , you lose top rake, and the work may tend to climb over the tool. Diagram El shows the normal tool; E2 shows a tool for sharp corners; E3 shows the flat that you can hope for a fine finish. A gauge for setting tools appears at F. You make it from sheet and angle metal, screwing on a strip for setting turning tools, and drilling holes for boring tools.  

 

 

LAST week I described how a 4-jaw independent chuck can be set up in a split clamp on the slotted cross-slide of a lathe, so that work can be held for centering, drilling and machining. Various settings were mentioned to show the scope of the arrangement which, for some things, exceeds that of the vertical slide and machine vice. Points in its favor are that the four jaws of the chuck are usually more accommodating than the two of the vice, and the chuck itself can be adjusted at angles in its mounting, or on occasion made to rotate. Even so, I do not suggest that the arrangement supersedes the vertical slide and machine vice. This week we examine in greater detail some typical settings. The basic one, as I mentioned a week ago, is with the axis of the chuck at centre height and its face to the headstock. Looking down on it, you see it as A. If the clamp is accurate, it should provide a precise horizontal mounting for the chuck, gripping by the boss of the back-plate, so that the face of the chuck is vertical.

 

 

If you are doubtful about this there are several ways of checking alignment; and if you find an error, you can correct it by packing under the clamp. One way of checking is to use a steel square with its stock on the bed of the lathe, and its blade up the face of the chuck. Alternatively, you can mount a test indicator in another chuck on the spindle , or on a driving plate, and let the plunger touch on the face of the four-jaw chuck. You should see the same reading top and bottom. Again, you can use the end of a cranked bar in the same way as an indicator. By the same principle, the crosswise setting of the work or of the chuck can be checked. With the test indicator, you should get the same reading at points P and Q on true work, or the same clearance here when using a cranked bar. When you test on the face of the chuck, you should get the same reading or the same clearance at points R and S. The chuck mounting can be adjusted on the cross-slide for this.

 

 

Chuck Mounting

 

 

The square mounting for the split clamp and the chuck is made by bolts in the T-slots of th creo ssslide, the holes and the slots having the same spacing. As a result, only small divergencies from the basic setting are possible, unless one side of the mounting is clamped to the cross-slide. Large angles can be taken from an adjustable angle gauge, or work a shop protractor, as a Bt, placing one side of this to the face of the chuck, or to the work, and testing points T an d U on the other side. Diagra Bm together with C shows how the base of the mounting is clamped. You tap the bolt hole in the base for a special stud with a larger thread at the bottom. Then a clamp or strap can be fitted to the base, with a short bolt in the T-slot and a block to take the reaction. The cap of the mounting you can fit by a nut at the top of the stud. With the mounting square or at an angle, you can adjust the chuck in it so that the jaws are square or at an angle to the bed of the lathe, as at D. For a square setting, checks are made at V and W with a surface gauge or indicator; or a steel square can be used for angle X. For an angle setting, an angle gauge can be used for either of the complementary angles Y, Z. These methods and their variations are, of course, applicable to work which is part-machined, or on which lines have been scribed in marking off. You can obtain further angles, or quick angular settings, after graduating the edge of the chuck back-plate and fitting a pointer to the cap with a short setscrew, as at E. Divide the back-plate as at F. Centre and machine a mild-steel mandrel for a lathe change wheel. Hold one end in the three-jaw chuck, with the change wheel keyed on, grip the 4-jaw chuck on the length, and support the other end by the tailstock. Use a detent to the change wheel and a pointed tool to the back-plate.


 

DIAGRAM A shows how a chuck can be mounted on a slotted cross-slide to hold work for drilling, tooling and grinding from the lathe spindle. In the illustration, a piece of steel is set up for grinding its edge square. I know that you can hold material on the topside, on the vertical slide, or in a machine vice on the vertical slide. With the chuck mounted in the clamp, which I have drawn at B, you can use it for other work. And so you have more power to your elbow-if your main interest is lathe work. The basic setting is the chuck at centre height. You are not limited to it. By arranging the clamp, the chuck can be below centre and with packing between the clamp and the cross-slide, it can be above. Its jaws, too, give height adjustment.

 

 

If the edge of the chuck overlaps the cross-slide, its use at centre height is limited to a face-to-face setting with the lathe spindle. But by packing under the clamp you can set the chuck at right-angles to the lathe axis. For other settings, you can twist the chuck in the clamp, so that jaws and work are at angles. With a normal vertical and horizontal setting, a shallow key, as shown, is needed for the bottom jaw. Diagram B shows you what the clamp is like in end-view. You can use material to hand for it. I suggest duralumin bar or aluminium-alloy castings. If you decide for the castings, you may be able to make your own from old car pistons. Alternatively, you can get some made from wood patterns. You need two : one for the cap, the other for the base. Two long bolts hold both these parts to the cross-slide, with nuts WX to the cap and nuts YZ to the base. To mount the chuck securely in the clamp, you need a smooth, parallel boss to the back-plate. If the finish is not up to this standard, you should remachine the boss, either with the backplate on the spindle, or with it face-to-face with a faceplate-having taken off the chuck. For a longer hold by the clamp, the heads of the setscrews can be reduced, or countersunk screws can be fitted. Another idea is to use a back-plate with a longer boss, which for this purpose need not be threaded.

 

 

How to do Chuck Mountings

 

 

With the clamp and ordinary bolts, the chuck can be used on the table of a drilling machine, jaws upwards, resembling the way that I suggested in a recent article. It serves as a machine vice-as at C, for odd-shaped material, and castings too big to hold in a normal machine vice. With the chuck and clamp mounted on the cross-slide, they form a specialised steady for operations in addition to those of which I wrote on November 15. For one class of work, they form a fixed steady, which is different from a fixed steady on the lathe bed. It is fixed in the sense that it does not rotate. For another class of work, and clamp form a rotating steady. Examples of the first set-up are shown at D and E.  You can hold multi-angular bar through the chuck for centring its end, D. Altematively, after setting the chuck at right-angles, E, you can hold a round shaft which is too big to go through the chuck. You support the free end of the bar or shaft to keep it level-and take off the tailstock if it is in the way. Both set-ups have their merits; and together they provide an effective alternative to the common method which employs a vertical slide and machine vice. Using one or the other, you can hold rough bars for centring, and shafts that have flats or keyways for which the ordinary fixed steady is useless.  In addition, you have the set-up at F for the unusual centring job. The other end of the work is in a chuck on the spindle. The cap of the clamp is loosened, for the chuck to revolve its boss well oiled. Then you run the tailstock barrel right through with the centre. This set-up always reminds me of the enormous Noble and Lund lathes with a chuck at each end that are used for machining forged steel boiler drums.  

 

 

50. Fixed Lathe Steadies
Mar 16, 2017

AN ACCESSORY considerably extending the range of work on a centre lathe is the fixed steady which is mounted on the bed to provide intermediate support for lona shafts and similar slender components in conjunction with the tailstock, or to support the outer ends of components having a lengthy projection from the chuck. Without such support, a shaft of any length even running between centres, is hkely to wobble and would certainly be unstable and subject to chatter under cutting stress. The normal steady supplied with a lathe is provided with three equally spaced jaws which ‘are individually adjustable to the work, and tipped or, capped with brass to obviate scoring. Each jaw is set just to touch and support the work? then locked by a nut or similar device. Frequent oiling is necessary and adjustments must be made as the jaws wear and bed to the work. In the absence of a steady, either as an accessory or for a particular job, a temporary one can usually be contrived from a wood block with an angle-iron mounting to the bed.How a steady extends the use of a lathe to work which could not otherwise be performed is shown at A.

 

 

An axle too large to pass through the lathe spindle-even if this is hollow-and too long to run between centres is required to be machined with parallel concentric ends. With the tailstock removed from the bed, a piece of over-length shafting is held in the chuck, while the free end is supported. in the steady and the turning-and any screw cutting-is done close to the chuck. Afterwards the surplus pieces are cut off-as far as possible by parting tool, then finishing by hacksaw for safety. A set-up for facing the ends of a long tube can be made in the same way if a mandrel is mounted in the chuck for the tube to be pushed on. On the same principle, shafts can be faced and centred, as at B. This is necessary when large billets are to be run between centres;. or when it is desired to centre material accurately, there being a minimum to machine from the outside afterwards. When a centre in a shaft has been damaged, such a set-up is necessary; and for truing, a fine boring or pointed tool may be required on the slide to avoid the swing and continuing wobble to which the centre drill would be subject. A setting for the steady jaws may be obtained by adjusting them with the ‘steady close to the chuck, then bringing it back to the working position. -Lifting and riding of the centre drill-from bad setting-is to be avoided on new work.

 

 

Fixed Lathe Steadies

 

Support for hollow work, such as for boring a large bush, can be provided as at C, when the adjustment of the steady jaws has an effect on the parallelism or otherwise of the bore-so checks and adjustments are necessary well before finished size is reached.

When prolonged use is to be made of the steady and frequent adjustments to jaws would be necessary-apart from the possibility of marking the work from restricted local contact-a

bush provides larger and more durable support, It can be from brass to fit the work and mount in the steady’ jaws, as at D. A screw in the side counteracts a tendency to rotate? And adjustment can be made by slitting lengthwise. To reduce wear, steady jaws in general use may be given a radius, as at E, using a reamer or boring tool in the chuck and adjusting the jaws to it. Using a boring tool, the steady can bc traversed by lightly gripping it to the bed, then pushing it along by saddle feed. A built-up steady, as at F, can be a wood block bored on the faceplate, or as at E, and bolted to a piece of angle iron which has a guide tongue for the bed riveted to the underside. A slit and a screw can provide adjustment.

 

 

Experience indicates that unless  design has arranged for it to be unnecessary, lack of suitable means of adjustment can be a handicap in producing good work on a machine, or set a limit to the useful life of certain of its parts. Consequently, commencing with the simplest lathe, various means of adjustment are common to a wide variety of machine tools-to ensure accurate fitting, smooth and rigid working, correct alignment, to accommodate wear or take end-thrust loads. One of the simplest means of adjustment of journal bearings is as A, a slit at one side through which the bore can be closed slightly to provide the desired degree of fit of the spindle, or take up wear. This may be used for the spindle of a drilling machine, the mandrel bearings of a small lathe, and on occasion is employed on the tailstock of a lathe for clamping the barrel-with a handle instead of nuts on the stud.

 

Simple Machine Adjustments

 

 

Fitting  Shims   

A normal split bearing with a cap and liners or brasses is as B. Several thin shiis each side, or one thick one, may be the means of adjustment-a thin shim or shims being extracted, and the thick ones rubbed down as necessary on a smooth file or sheet of abrasive cloth on a flat surface. If, after rubbing down thick shims, the spindle is gripped too tightly, a thin metal shim or strip of paper of suitable thickness can be inserted, since the caps of such bearings should be pulled tight to the housings or body portions. Thus, with a little trouble, bearing adjustment can be regulated to a nicety, as is necessary for smooth running of a drilling machine spindle or production of chatter-free work on a lathe.A simple bearing for light duty, and with the advantage of taking both journal and thrust loads, is the coned type, C, which is employed for countershafts, overhead shafts and treadles, mostly of older lathes.Each end of the shaft has hardened disc contaimng the countersink. The hardened pointed screw passes through the machine frame and is held by a locknut. In amateur workshops bearings of this type can last literally a lifetime, with occasional lubrication and slight adjustment.For thrust loads only, as on a drilling machine, or a lathe with a solid spindle a ball may be employed in a hardened screw. This type of thrust is used on old-type lathes with opposed cone journal bearings. These bearings can be adjusted for play by locknuts on the spindle at the far end from the chuck, but the ball thrust is essential or the bearing nearest the chuck will, run tight or seize under the thrust of cutting. The principle is as D.

 

 

 

Slide  Adjustments   

No less important than adjustment of spindles is that of carriages and slides. For slides on the normal flat-topped guide or lathebed, adjustment is normally made through an angled strip or gib piece, E, which can be adjusted to the vee by a number of screws, then held by setscrews or studs-these, of course, have to be slightly loosened to make adjustment. Actuated by its screw or feed, the slide should move reasonably freely, and without shake.

A simpler fitting on some small machines and lathes is as F, where instead of being angled the strip is parallel and adjusted to the vee by a number of pointed screws which serve to locate and hold it. This means of adjustment is less effective than the other for controlling play and vibration in cutting.Some lathes with flat-topped beds and headstocks located from central guide faces have a means of head- stock lateral adjustment as at G. The tongue portion of the headstock fits with slight clearance between the guide faces, and has two adjusting screws each end which can be turned outwards to wedge between the faces. Thus, by regulating the screws, the headstock can be trued laterally to produce true turning or boring in the chuck. On feedscrews,’ locknuts and a washer are normal means of effecting adjustment and taking thrust. 

 

 

48. Some Facts about Tapers
Feb 15, 2017

APART from many other uses a taper is often the means of securing a flywheel, a sprocket, a gear or pulley to a shaft-either with or without a key. For such purposes, a taper is usually mechanically more satisfactory than a plain interference fit between shaft and bore, a sliding fit with a drive-in key, or a sliding fit with a locating shoulder and, a nut for holding. The angle of a taper has a considerable influence on the grip exerted when components are pulled together ; and the smaller the angle, ‘or the less the change in diameter for unit length, the more powerful the hold. 

 

Some Facts about Tapers

 

A taper may be dimensioned or designated in two common ways, A. The angle, P, may be given irrespective of the size of the shaft, which may be convenient when the angle is a whole degree, such as 5 deg., or whole degree and a simple fraction, such as 6) deg. Alternatively, the smaller and larger diameters, Q and R, may be given and the distance, S, between them. In such an event, the taper may also be given as so much per foot or per inch as the case may be. On a lathe, a fairly-quick taper is machined by setting the topslide at an angle and using this for machining; while a slow or gradual taper longer than can be machined from the top-slide is produced by setting over the tailstock, or using a set-over centre when the work is mounted between centers. Again, on lathes so equipped, a taper turning attachment may be used to control movement of the cross-slide, leaving the work in longitudinal alignment with the lathe bed. Some experiments are virtually always necessary in setting up for machining a taper, since no graduation -particularly of the top-slide is sufficiently accurate. Moreover, i t is important for the tool to be at centre height, otherwise, variations in shape and angle occur, B. When the tool is at centre height it lies on the horizontal centre line of the shaft, where the slide angle is the same as the taper. If the tool is dropped, however, to’ plane, T, the effect on the larger diameter, U, is much less than on the smaller diameter, V. 

 

 

In obtaining well-fitting tapers, size, angle and finish, both externally and internally, are extremely important. If one has the choice when fitting two parts on a “ one-off” job the shaft is better finished last, as it is the more easily adjusted for size to secure longitudinal location, and the simpler to provide with a good finish, or on which to correct small inaccuracies, from careful use of a fine (Swiss) file and/or abrasive cloth. Variations in longitudinal location with size are shown at C, where the component moves from W to X as the bore is increased. If there is no choice in procedure, as when fitting a new sprocket to an existing shaft, the taper is picked up on the topslide with the shaft in the lathe and a mandrel turned to the same taper, but smaller. This is used for preliminary testing, though the final testing should be with the shaft itself. Illustrations, D, show some ways in which an internal taper can be faulty The bore may be large on the outside or inside, when on entering the mandrel and “ feeling” slackness can be noticed. Pushing in the mandrel and twisting also shows where the taper is touching.

 

 

 

When the taper is faulty, the top-slide requires m-adjustment. Finish is important, since if the mandrel rides on ridges the fitting will be poor though the angle may be correct. Slight correction and improvement follows from grinding the parts together, but too much reliance should not be placed on this. For small bores, silver-steel tools, E, can be made by bending as Y or turning to leave a diameter, Z, both of which can be filed to shape, then hardened and tempered. Of course, with a taper reamer available, or made from silver steel, sizing and finishing are simplified.  

 

 

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