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USING the same principle employed for the faceplate of the large industrial lathe – which often serves as a chuck – the faceplate of a small lathe can be provided with dogs or clamps for holding components which require to be gripped edgewise, as in chuck jaws. The components I have in mind are those which cannot be merely clamped back to the faceplate, and cannot – because of their size or irregular shape – be held in the ordinary three-jaw self-centring chuck, or the four-jaw independent type. For such components, dogs or clamps convert the faceplate into an extra-large, extra-adaptable independent chuck, when they are mounted in place with bolts through the slots in the faceplate, or through holes which have been drilled. On slides or tables with T-slots, they are equally useful for side-gripping components as in machine vices. The advantage here is that in their setting they provide the widest possible choice of angles and positions through which such grip may be applied. 

 

How To Use Faceplate, Dogs and Clamps

For a large lathe, dogs are of special construction and the faceplate, when intended to be used as a chuck, is adapted to take them. The bases which are bolted to the faceplate are short box-like steel castings, the sliding jaws of forged steel, and the feed screws of heat treated nickel chrome steel. The bases have locating plates or tongues to engage any of a series of recesses in the faceplate, and so prevent sliding under heavy pressure: Radial setting can, of course, be wherever required, with the jaws pointing to provide a hold on components either from outside or inside. For a small lathe on which the faceplate may only occasionally be used as an extra-large chuck, dogs or clamps can be of much simpler construction. The bases can be of various types, built-up or solid, but without sliding jaws, for the pressure screws themselves can perform that function in securing components, bearing either at their ends or their heads, pointed or rounded, and directly on components or through packing pieces. Mild steel which can easily be brazed or welded should be used for built-up bases, but duralumin or aluminium alloy is suitable for solid types. With either, tirm bolting to the faceplate should be sufficient to prevent slip, so that only in exceptional cases should dowelling be necessary. For pressure screws, high tensile hexagon-headed setscrews (threaded the full length) can be used in 1/4 in., 5/16 in. and 3/8 in. dia., and with BSF threads. 

 

 

 

An example of work set up through dogs or clamps on the faceplate is as at A. each clamp consists of a flat base with brazed or welded-on tapped bosses, so that two pressure screws can provide a balanced grip with a single holding bolt. The grip with this arrangement is better than obtained from a single pressure screw, and so is always to be preferred where there is sufficient length of flat face. Besides this, it is not necessary to do any drilling for holding through the faceplate slot, and should drilling be essential on any occasion, there is need for only one hole.  

 

 

The  Bases :    

Short pieces of angle-section steel with nuts for extra length of thread make bases for simple single-screw clamps, as at B, where the pressure screws bear through their heads and the work is hollow and supported inside by blocks bolted to the faceplate. The bases of the clamps can be secured by countersunk screws with nuts at the rear of the faceplate; and with a permanent fitting for screws, each can be nearer to the angle of the section and placed in position before the nut for the pressure screw is brazed or welded on. Solid bases for single-screw clamps can be as at C, for securing by countersunk screws (1), when the material may be mild steel or aluninium alloy, or by a stud (2), when the material should be mild steel, with a length of thread giving a firm hold. Using two holding bolts - more suitable for T-slotted slides, bases can be as at D, solid or built-up. On any clamp, slight inclination of the screw(s) is advantageous, while holding bolt holes should be drilled to leave a good length X for reaction.An example of work set up through dogs or clamps on the faceplate is as at A. each clamp consists of a flat base with brazed or welded-on tapped bosses, so that two pressure screws can provide a balanced grip with a single holding bolt. The grip with this arrangement is better than obtained from a single pressure screw, and so is always to be preferred where there is sufficient length of flat face. Besides this, it is not necessary to do any drilling for holding through the faceplate slot, and should drilling be essential on any occasion, there is need for only one hole.  

 

MANY milling operations in the lathe can be performed with the work mounted on the top-slide, or on the cross-slide table, or on an angle plate attached to this table. They are operations involving lines of traverse and feed into which height adjustment does not enter, and for numbers of them an initial setting of work at correct height is essential. Naturally, this is a process requiring time and care; given means of height adjustment, it is greatly expedited. There are other operations, in which height adjustment is required as part of the machining procedure. Widening the slot in a piece of material by machining along one edge with an end mill is an example; and for such operations as this, a vertical slide on the cross-slide enables the material to be raised or lowered as necessary. The same is true when all that is required is an initial height setting of work in relation to mill or cutter. The vertical slide admits of quick adjustment. 

 

 

How To Use A Lathe Vertical Slide

 

Usually, a commercial vertical slide is made from castings, and often has provision for tilting from vertical for angular feed. The simple non-tilting slide comprises two castings: one for the base and pillar forming the guides, the other for the table. The tilting slide consists of three: one for base and pillar; one for the guides; the third for the table. Both tables are slotted for square-headed bolts. For a small lathe, a simple non-tilting vertical slide can be built up from mild steel bar and flat material, as at A, B and C. Certain machining operations – such as those on the guides and table – which can prove to be problems, are thus avoided; for the flat faces of the material serve as guides, and tapped holes in the face of the table can take work-holding studs, obviating the need for tee-slots. The base can be a disc cut from round bar, or sawn and turned from flat material then bored to locate the machined end of the square bar used for the pillar – for that is the section combining the advantages of simplicity, rigidity in all directions, and ease of mounting to the base – by brazing or welding. The square bare can be faced in the independent chuck – or if too much overhang is involved, it can be filed reasonably true for centre positions to be located with depth gauge and scriber, or on a faceplate using a surface gauge. Then, with centres drilled, support can be given from the tailstock for facing the ends. Even with considerable overhang, drilling right through can be done, with care, operating from each end. For the major part of the distance the hole should be cleared for the feed screw – which can be of vee or whit worth profile. 

 

 

Four bolts hold the table to side plates and a backplate-fitted to slide on the pillar. These pieces can be faced in the independent chuck, or by mounting each on the topslide, or on a block on the cross-slide table, and using a face mill to true it. The width of the side plates should be the same as the pillar; then working clearance can be given by shimstock or paper at the faces up to the backplate. One side plate can be fixed through close fitting bolts and holes, and the other made adjustable through clearance holes, a small bar opposite each bolt being provided with grubscrews. Holes in table an backplate take the turned ends of the bars. Other details are the pressure screw with a flange to abut to the thrust plate, and a taper-fitted ball handle with a collar between it and this plate to eliminate end play. Holes X in the face of the table are tapped for holding studs. For the pillar to be square with the base, the base should be faced on a set-up as at D. A centred plug, or centred long bolt, stepped under the head, should be fitted; then, adjusting the jaws of the independent chuck, positions Y and Z on two faces at right angles should be brought parallel with the lathe axis. 



 

THERE is an old saying that a bad workman blames his tools; the converse of this is that a good workman is one who knows how to put his tools right. We don’t propose to explain how to correct an inaccurate lathe, but only to show how it should be tested for faults, which, after all, is the essential preliminary to making up your mind to do something about it. Now it might be thought that the quickest way to test a lathe machine for truth would be to check the work produced, but anyone who has tried this way will agree that it is slow and unreliable. It is seldom realized how much spring there is in the work itself, even with the lightest of cuts. For example, if the headstock is adjusted so as to turn parallel a piece of bar held in the chuck, a cylinder bored immediately afterwards will be found to be most unaccountably large at the back end. The error may not be great if the mandrel is a stiff one, and the work rigid, but it will be there all the same, and repeated attempts to get things just right by this method generally end in the unfortunate owner wishing he had left well alone. To get the best performance from your lathe machine you need to check the accuracy of its working parts. Modern lathes have accuracy built into them, but there may be some parts that are not accuracy or properly aligned. Some of these problems can be easily fixed, and some require more work, but as we describe each of these problems we sill state how much deviations is acceptable (tolerance), and what operations would be ill affected by these errors. That way you can decide if you need to fix the problem. Fox example, if you never drill from the tailstock, or use the tailstock to steady work held in a chuck, then the alignment of the head and tail centers is not very important.

 

How To Test The Accuracy Of Your Lathe Machine

 

Before getting into the fun of working with a Lathe Machine, a few words on the subject of workshop safety may be in order. In an industrial environment, many activities involving machine tools are governed by legislation aimed at improving health and safety. One of the delightful aspects of the workshop lies in “escaping” from the worldly cares outside and as such, in our leisure pursuits, much of such legislation does not apply, and responsibility for safety of both ourselves and our visitors, lies very much in our own hands. A sensible approach to safe working practices involves first an appreciation of factors which can give rise to injury (and those parts of the body at risk), and second, a common sense attitude to working around these factors. 

 

 

Fingers and hands

While a small machine such as the Bench Lathe Machine has much less power than a heavy-duty production engine lathe machine. But the inertia of chuck and work spinning at maximum speed would certainly be sufficient to cause severe damage to a misplaced finger. Another of the regular injuries is laceration due to sharp edges, which may be the tool, the work, or the swarf. Ribbons of swarf may look like bits of Xmas decoration, but think of then as long thin ragged razor blades. So when clearing swarf do not use fingers.

 

 

Eyes

Some materials, notably brass, produce swarf, which comes away in small needles at high velocity. If you have the misfortune to get some of this in an eye, then it is almost certainly a trip to hospital, where (being non-magnetic) it will be removed manually. Safety glasses are cheap and will prevent this. They should also be worn when grinding tools on the bench grinder.

 

 

Feet

In an engineering factory you might wear safety boot or shoes rated so that you could drive a car over your foot without damage to toes. In our amateur workshop, most of what we handle will weigh perhaps not too much heavy. But a pound or half kilo dropped from bench height would cause a fair amount of bruising, so trainers or open toe style sandals may not be the ideal footwear. Our version of Murphy’s Law also states that if you drop a sharp edged object on to your foot, it will land sharp side down.

 

 

Hair

Long hair can be caught by a rotating shaft and wound in, leading to probable head or facial injury. Tie hair back or use a net.

 

 

General clothing

A tie presents the same form of risk as long hair. Preferably remove it or at least ensure that it is tucked in under a sweater. Loose fitting sleeves are similarly not recommended. Open collars can present a problem when machining at high speed. Hot swarf dropping down inside the neck can be painful and can cause involuntary movement leading to a secondary risk.

 

 

Electrical safety

If you have purchased a new Lathe Machine, then all should be well. If second hand, then it may be worth checking that the plug, cable and connections are in good order. If you are using an extension cable, route it in such a way that you won’t trip over it. Connecting via an earth leakage or residual current circuit breaker is a sensible precaution. Industrial machining processes often make extensive use of water based coolant to speed up the cutting. Clearly, water and electricity (especially at mains voltage) are not happy bedfellows. Using of the proprietary cutting compounds will be a safer option. The most important test of a lathe machine lies, no doubt, in the accuracy of the work and the manner in which it is produced a skilled operator being able to overcome considerable basic inaccuracy. Even if the work is of a relatively simple character, ample scope for error exists-provided there is sufficient variation to test all aspects of alignment. This is to say, a lathe machine may be accurate for one type of work but not for another, and experience of it can indicate where to expect errors, though the reason why may not always be immediately apparent. However, there are various simple tests which are largely a substitute for “work experience” and which can be useful for discovering errors, for truing the machine (if possible), or on occasion for setting up. 

 

 

 

 

 

 

A simple but important test, photo A , is the meeting of headstock and tailstock centres. When the fixed centre has noticeably dropped, wear of the underside of the tailstock and possibly of the bed itself is indicated. The effect on between-centre turning may be small or non-existent, but care will be necessary when using centre drills or boring cutters from the tailstock-a degree of “lift” then being necessary for the tools to centre. The same effect also obtains when supporting chucked work from the tailstock. This test should be made with the barrel both close in and well extended. A sideways error of the same kind can often be corrected by adjusting the tailstock. A more severe test of the same sort, photo B, can be made with an indicator, which can be a dial type or one of the small inexpensive varieties. The indicator is mounted in a chuck or on a driving plate with its plunger bearing on the fixed centre. Then the lathe machine spindle is turned, when a steady reading shows perfect alignment, using a small mirror to see the instrument upside down and from behind. Where there are variations in readings, as is virtually always the case, it can be seen in which direction (vertically or sideways) they occur, and the tailstock adjusted to correct sideways error. A live centre test for running truth, photo B, can be made of the one normally in the spindle and of others of the same taper with the indicator mounted on the slide-rest. This can sometimes reveal that the centres themselves have not been ground true; and in use it may be advisable to keep them to one position-spindle or tailstock-marking for fitting in a certain manner.

 

 

General alignment

A test for general alignment of headstock and tailstock for between-centre turning can be made employing a mandrel, photo C. Any suitable piece of rod can be used, carefully centred, reduced in its length, and with the ends turned the same size. A tool mounted on the slide-rest can be brought close to one diameter, leaving a small gap, then the gap checked on the other diameter, a piece of white paper on the bed providing a light background against which to see the gaps. Finally, the tool may be set to touch the diameters lightly when traversing the saddle. This aids reasonable setting of a lathe before work begins, and as an alternative to a tool an indicator can be used. A faceplate may be checked with a rule, photo D, and when mounted on the spindle and rotated is tested for face wobble. If chuck work is machined true, a test can be made on the faceplate of cross-slide alignment in two stages, photo E and F, using a tool or an indicator. Testing along the near side along line X-X1 in the above photo, no error may be shown if the faceplate was machined on the lathe, for alignment corresponds to the cross-slide. Testing on the far side, however, on line X2-X3, any error is doubled and can be easily seen. Topslide setting can be tested as photo G, an indicator on a mandrel and a rounded rod on the slide-rest. With the slide out of alignment, movement is along such as X4-X5, and checking with saddle traverse, variations are shown, whereas with a true setting readings will be all the same.


 

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