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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.  



AN advantage of the single-web crankshaft with open crankpin-and of certain built-up types-is that the connecting rod can have a solid big-end eye, which simplifies its construction, makes for strength, and reduces bulk and weight-all important factors, and particularly so for high-speed engines and for two-stroke engines where dead space in the crankcase should be kept to a minimum. In the interest of reducing the weight of the connecting rod, while retaining a high degree of strength, duralumin is often used in model petrol engines, and in itself provides a good bearing on soft-steel or hard-steel gudgeon pins and crankpins. Steel may be used, but it is heavier, and the eyes require bushing with bronze, brass, or duralumin-except in some instances where the gudgeon pin may be a fixture in the small end and oscillate in the piston bosses. Brass or bronze may also be used for the connecting rods of simple engines, of moderate speed and power, and both are heavier than steel, though neither requires bushing expressly, but only to facilitate overhaul when wear occurs, thus avoiding renewal of the whole connecting rod.


Machining Simple Connecting


The simplest section for the length of a connecting rod is a rectangular one with rounded sides; and on a weight/strength basis it lacks little beside the familiar I-section, which is milled each side to leave a narrow central web. The connecting rod of rectangular section, however, can be entirely finished by turning methods and some handwork-without the need for milling where there are no facilities for this. Using a piece of suitable flat bar to make the comecting rod, it is faced flat one side by filing or machining a light cut, in the four-jaw chuck. Then the centres of small and big ends are marked, and these bores machined, clamping the bar to the lathe faceplate-preferably leaving the bores undersize for final finishing later by machining or reaming. For machining the web, the bar is centralised and clamped, and facing cuts taken across. Final smoothing may be done with a file, with the bar removed ; and for machining the opposite side of it, a piece of packing of appropriate thickness should be clamped against the faceplate, as at A, to provide support for the web.



The small-end and big-end bosses, which will be circular, can be produced partly by sawing and filing, partly by machining. Sawing and filing are recommended for removing the surplus material; and for holding. the connecting rod securely in the vice. without risk of damage, suitable hardened steel plugs should be made for each end, as at B. Following this, the connecting rod is mounted on a mandrel in the chuck (one mandrel for each end), and the bosses are turned back to the web-slightly tapering them towards the outside

if required. Surplus material along the edges of the web can also be removed by carefully sawing and filing; and eventually there will remain only material on the bosses in line with the web. Plugs can then be used as filing guides particularly where the outside edges of the bosses are tapered, as with larger plugs, the file will clear except at the centre. Alternatively, material in line with the web can be milled or “ turned ” off. For milling, as at C, the mill is run in the chuck, and the connecting rod mounted on a bracket on the top slide. A stop prevents the cutter gathering on to the web; with a light feed, the connecting rod is pulled round by hand. For “turning,” as at D, the connecting rod is on a mandrel in the chuck, which is pulled round by hand for each cut. Connecting rod centres may be accurately obtained, as at E, using a plug Y in one bore, for dimension X to be measured over a hollow “button” Z, which is then set to run truly for machining the other bore. 



46. Marking Centers Squares
Jan 20, 2017

HERE are three methods employed for the essential work of finding the centres of shafts or discs without setting them up in a lathe; 1, by the centre head of a combination square; 2, by jenny calipers-also called odd–leg or hermaphrodite calipers and 3, by surface gauge and wee blocks on a surface plate.The first two are hand methods while the third is a shop or toolroom method. The use of a bell centre punch (a metal cone with a punch in the centre, placed on the shaft and struck with a hammer), which is a fourth way, is neither so universal nor so accurate as the others. 


Hand Methods

The centre head has two arms disposed at right–angles and the blade of the square, or rule, fits in centrally and is clamped by means of a groove. The edge of the blade passes centrally across the shaft. Thus, the tool has only to be held firmly and moved round the shaft for several intersecting lines to be scribed.Jenny calipers have a leg with a scriber point and the other with a small step to rest on the edge of the shaft. The leg with the step is held firmly at one spot while the scriber leg is swung in an arc slightly beyond the actual centre of the shaft. This being done at four positions round the circumference, a tiny square is formed–in the centre of which the centre punch dot can be placed.


Marking Centers Squares



Surface Gauge Method

The surface gauge and vee blocks, normally used on a surface plate, can be employed on any flat surface like the bed of a machine. The shaft is rotated in the vee blocks for several lines to be scribed horizontally. These need not pass across the centre. If the scriber pointer is a little above or below, a small boxed in area is formed–centrally in which lies the shaft centre.The following method is as good as any. Scribe a horizontal line, turn the shaft through 180 deg. (approx.), scribe a second line; turn the shaft through 90 deg. (approx), scribe a third line, turn the shaft through 180 deg. (approx.), scribe a fourth line.To mark a square or hexagon on a shaft, using vee blocks and surface gauge, its centre should first be found, lightly centre punched and a horizontal line scribed through it. In marking a square, an engineer’s square is employed for the vertical centre line; for a hexagon, a 60 deg. Square or a combination square is used-first one way, then reversed, so producing two sloping lines. In this and subsequent work, vee blocks having horizontal grooves are advantageous, taking clamps to hold the shaft firmly.


Marking The Flats

To mark the flats, it is necessary to know the height H for the scriber pointer to be set above or below centre. This is calculated from the diameter of the shaft’ and its radius R. , For a square, R is multiplied by 0.707, for a hexagon by 0.866. This dimension H is obtained on an engineer’s steel rule with dividers. Then one leg of the dividers is placed in the shaft centre, and highest and lowest positions marked-to one or other of which the surface gauge pointer is adjusted.In marking, a line is carried across the end of the shaft and along the side(s) as required. Then the shaft is unclamped, and for a square turned through 90 deg., as checked by the engineer’s square, reclamped, and another flat and side line scribed-this being done for all four. For a hexagon, the procedure is similar, but either the engineer’s square or the 60 deg. Square can be used for the settings. At the finish, the side lines act as guides when filing the square or hexagon in the vice. Castings and parts can be marked off with the surface gauge, finding the centres, boxing them in with or scribing circles with dividers, then placing centre punch dots for reference when the holes are bored. 



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