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41. Self Feeding Facing Tool
Oct 23, 2016

In meeting the needs of a small workshop, a lathe may perform many operations that are work for specialised machines in a large machine shop. It is not unusual for features on components of a single model or piece of equipment to require the maker’s lathe to function as planer, shaper, grinder, milling machine and boring mill-as well as in its ordinary capacity. Much ingenuity is necessary in setting up and machining components-and one may regret the lack of facilities provided by specialised machines, particularly when one is working near the full capacity of the lathe. An occasion of this sort occurs when there is need to face a large surface or series of bosses on a component which cannot be swung on a lathe principle, or moved across the bed past a tool or cutter in the manner of work on a milling machine. What is needed then is the feature of the special head on a boring mill by which a tool can be swept, not on a fixed radius, but in a flat spiral. Given this, the work can be fixed either to the slotted saddle or to the bed of the lathe-which is used to maximum capacity.

 

 

Self Feeding Facing Tool

 

 

Many operations can be performed, of course, with a tool in the chuck or on the faceplate, sweeping on a fixed radius; but to machine a flat surface with it, cross feed is required, and is not possible at full capacity, though it is another matter when, as now indicated, the tool besides being rotated is fed on an increasing or diminishing radius.The easiest way of providing this self-feed for a tool is an arrangement as at A, with the feedscrew turned by a star wheel from a peg on the lathe bed, as at B. Simple guides for the tool block can be from flat material, attached to the faceplate (or to a large chuck backplate), as at C and D. A right-hand thread on the screw draws the tool block towards the centre, retracting the tool from the radius giving the large circle X. To return the tool, a loose handle can be fitted to the feed screw-or it can be rotated with a screwdriver via a slot in its end. For a fixed components, depth of cut must be provided by setting the tool further out of its block. It can be done without special provision for the type of work performed, although a taper-ended screw from the end of the block to the bottom of the tool would give fine adjustment.

 

 

Rate of feed of the tool is governed by the t.p.i. on the screw which is moved 1/5 turn for every revolution of the faceplate. Divide 1,000 by 5(200), and the answer thus obtained by the t.p.i., gives the feed per revolution in thou. With a screw of 26 t.p.i. which it is convenient to use, the feed is just under 0.008 in. per revolution. This is satisfactory for a facing operation if the tool has a small flat at its cutting edge. Back gear for slow speed should, of course, be used. The tool block is mounted to its flat base by countersunk screws; and the two are drilled and tapped at the joint line for the feedscrew. If adjustment is required to give a good working fit for the screw, it can be provided by carefully facing (draw-filing) the bottom of the tool block. Drawfiling can likewise be the method of fitting the guides to the flat base of the tool block, to ensure the firm support that is essential to obviate chatter in machining. To the same end, the extension of the tool from its block should be a minimum. Any or all of three features in the drive will safeguard it from jamming if the lathe is left running. The feedscrew may be given a plain portion on to which the thread in the block can run. The star wheel is gripped between locknuts, admitting of lip under heavy thrust. And the peg for the wheel is set in a plate which is tightened just to hold in normal working.

 

 

40. Cutting Discs and Rings
Oct 05, 2016

CUTTING a disc or ring neatly from sheet material invariably requires swinging either the tool or the material in a circle. Merely marking the material and cutting it with scissors or metal shears produces inferior results, even on outside edges, and the difficulties are obviously increased with inside edges. Successive cuts with scissors or shears are never really uniform, and contours are a series of deviations and flats approximating to circles. In addition, if a material is soft, like thick sheet cork, it can be forced out of shape and chipped at the edges by local pressure. For material like cardboard, fibre, composition sheeting, thin plywood, and even soft metal, the type of washer cutter at A is very suitable With the blade set to radius and the centre point pressed well down, the tool can be turned in regulated cuts. Except on thin material which can be severed at a single rotation, the first cut should be moderately heavy to leave an indentation to help as a guide for following cuts. A firm backing should be provided by way of a flat board.

 

Where, owing to the thickness of the material, several turns must be made, the centre can be worn and the blade will wander from the original cut. To prevent this, a pad can be used at the centre, such as a piece of flat steel with a small hole for the point. A piece of square steel with the corners turned down can be used to grip the material when it does not matter if the material is marked. Working from both sides is advantageous in cutting a disc or ring from plywood; and it is helpful to drill a centre hole into which a small bush can be fitted, such as a short piece of tubing, to take the point of the tool. Cuts from opposite sides then meet at the centre without risk of wander. Where centre marking is not possible a piece of material with the centre can be temporarily stuck on; and in the case of glass, a suction cup with a moulded-in screw can be usefully employed ( such as is used to fix demisters to windscreens ). The screw locates an arm with a turned-up end to which a glazier’s diamond can be clipped, as at B. Adjustment is not usually necessary to cover a range of sizes; and having clipped the diamond tool to the arm, the radius can be marked and the bole drilled.To break out the circle afterwards, straight cuts can be made at the corners, as at C, so pieces X can be taken off. Then pieces Y will substantially break away. Fragments left can be “nibbled” and crumbled off with flat-nosed pliers, and the circle finished by careful free-hand grinding edgewise on a wheel.

 

 

Cutting Discs And Rings

 

For soft, easily deformed materials, a thin sharp blade is required. There is probably nothing better than piece of razor blade. Using this, a tool can be as at D, the portion of blade held by a screw and washer to the turned-down end of the arm, which should be slotted for setting with locknuts to radius on the stem. This last can be mild steel stud, with a flat handle at the top, and pointed at the bottom by turning down and filing in the lathe, then case-hardened. Alternatively, it can be drilled and a gramophone needle fitted.For sheet metal, cutting on the lathe is generally best with 2 backing provided by plywood or board. In large sizes this can be fixed to the faceplate with metal screws with countersunk heads. The sheet to be sut can then be attached with waste portions, using small bolts or wood screws. A narrow V-tool, light cuts and use if back gear are essential. It is advisable for the centre of the sheet to be held up by a pad from the tailstock or when severed, it may swing off centre and jam. A friction grip on this principle between wood pads is sufficient for edge-machining a small disc, as at E, a steel washer taking the trust of the tailstock centre; and with concavo-convex faces on metal pads, as at F, a transparent disc can be shaped, machined and sprung into the bezel of an instrument as a substitute glass.

 

 

39. Milling on Angle Plates
Sep 18, 2016

WITH an angle plate mounted on the cross-slide (as described in my last article), the effective capacity of the lathe is extended over a wide range of milling and boring operations. The outcome is that one can undertake machining of certain items of equipment, or parts of models, which were previously beyond one’s scope from sheer inability to swing them or otherwise set them UP. Many operations on smaller components are also facilitated when the slide-mounted angle plate is the only alternative to the top slide for setting up – the lathe having neither a vertical slide nor a cross-slide with slotted face. Small components which can be set up by straightforward clamping can, like large ones, be mounted direct to the face of the angle plate. For others with right-angle faces, it is advantageous if the angle plate is supplemented by a smaller one? Or by right-angle blocks, providing either a horizontal platform or faces to which components can be attached. For many operations, especially on large components, it is necessary to set up to horizontal and vertical centre lines-which are first marked on components in normal ways. For the horizontal centre line to the lathe axis, the surface gauge can be used from the lathe bed, aligning its point to the centre line at each end of the component. The height of the point is set from a horizontal line on a piece of material in the independent chuck. This line is itself set to centre height by adjusting the chuck jaws and testing at 180 degrees. Then the scriber transfers the setting to the component.

 


Milling on Angle Plates


 

For the vertical centre line, a flat face is needed at the lathe axis extending from the chuck. It may be the face of a half-round bar, or a piece of rectangular bar off-set in the independent chuck. With the face at the axis, a small straight-edge can be held or clamped to it, and set vertically by turning the chuck. Then the vertical line on the component can be adjusted, by slide feed, across to the straight-edge; and for a boring operation, the slide is clamped. The cast bed of a horizontal steam engine is a fairly common example of outsize work. From inability to machine it, the underside may have to be filed true, the casting being screwed to a block of hardwood in the vice. Flatness can be tested in the surface plate. For milling the crosshead face, a set-up can be made on the angle plate, A. Ordinary clamps may be used mstead of lugs, or bolts may be passed through the bed. Alternatively, a strap bolt may be used on the cylinder mounting face; it consists of a stud brazed or welded to flat material. After milling the crosshead face, turn the angle plate 90 deg. To deal with the cylinder mounting face. For this, to get to the lathe axis, the engine bed is mounted with the crosshead face to the angle plate, with packing if necessary, B.

Machining outside the flange, and boring for the spigot on the cylinder cover, should precede the facing operation, while the centre line remains to give the setting for clamping the slide. These operations are performed with an outside tool and a boring tool, C1 and C2.

 

Ordinary facing and outside flange machining operations, of which these are examples, can be performed with tools in blocks, adjusting the chuck jaws for swing and radius. Boring operations require short tools, similarly set to radius by the chuck jaws. For narrow slots, such as ports and keyways, end-mills are advisable; though on occasion some extra width is possible by wobbling slightly in the chuck. For operations like these, the second angle plate mentioned (mounted on the main one) facilitates setting up, though by the use of clamping plates and blocks, set-ups can be made without it, D. The engine cylinder, for example, can be bolted between two plates W-X which are fitted by studs to blocks Y-Z, also tapped for studs to hold them to the angle plate. The crankshaft can be set up in split blocks, one of which is drilled and tapped for studs. 

 

 

38. Accuracy in Details
Aug 23, 2016

A good standard of workmanship springs from unrelaxing attention to details in tools, equipment and parts of models. Without it, major components will not fit properly and function efficiently. Variations in numerous small parts detract from the satisfying impression which is created by uniformity. This becomes plain when you consider a few examples. An unchamfered bore will not allow the spigot of a cover to enter fully. A drill which is badly ground and wrongly used will not make holes of required size. You have loose fits on bolts and reduced depths for threads in tapping. These are faults in the fitting and functioning of parts-faults which can be avoided by attention to details.The importance of looks can be appreciated when we consider a bad case-a brass nut for electrical work among five steel nuts in the circle of six on a cylinder cover. Here the difference is obvious; but consider other variations. Nuts may be steel, but may vary slightly in depth of chamfer: and so may the washers used with them. Studs may vary in length, so that different amounts of thread project through the nuts. In all this, mechanical function is not involved. The nuts, washers and studs may be right for the job, and acceptable individually. It is when they are brought together in an assembly that their differences can be seen.

 

Accuracy in Details

 

 

To note such things is not necessarily to act the critic, the quibbling perfectionist. It is to exercise faculties that we begin to stimulate on taking up a craft. We all know the difference between tea and coffee, as between brass and steel nuts. But without being told, a wine-taster may know the year, the district, the vine-yard, of what he savours. A basic job in the workshop is drilling, which must be followed by burr removal abd chamfering for neat sufficient results. The sharpest drill leaves a small burr as it enters most metals, and a larger burr on breaking through, al. Blunt drills leave larger burrs than sharp ones. Break-through burrs can be reduced by slow final feed. Burrs can be filed from holes with reservations for machined surfaces, and holes may be chamfered with a drill, A2. The drill can be twisted in the fingers for small jobs and run in a drilling machine for large ones. It must be big enough to have no tendency to drag into holes. You often find that a drilled hole is largest in the mouth, especially when the drill has wobbled, or has been off-axis on the lathe. Wear occurs until the drill steadies and centralizes. In lathe work, you follow the drilling with a facing cut on line TU. In running into solid metal, a drill is guided all the way by its tip. When this is off-set, R, because one of the cutting lips id longer than the other, the hole is made oversize V as far as the break-through end, where the tip clears and the drill cuts nominal size W. It will do this all the way and produce a good parallel bore, if a pilot hold is drilled first.

 

 

Drilling a biggish true hole in thin strip metal is difficult unless you go the right way about it. With free drilling the hole is ragged, C. For accuracy, drill a small hole in the strip and in each of two pieces of thicker metal. Clamp the strip between them, aligning the holes with a parallel pin, and drill to the required size. A small washer can be drilled larger in the same way. Subsequent washers must be aligned by stepped pin, D.The action of tapping a hole pulls up a small burr, E1, which should be removed with a drill to leave a chamfer 2. A stud, 3, can then be tightened without the lifting of any part of the surface round it-an important detail, as a stud tightens by binding at the surface. A substitute on occasion is a cut-off screw, 4, which tightens at the bottom of the hole. You can level by filing, on line XY, using a block with a nut. A centre in a shaft is an eye catching detail which should be neat, F1. As this is not large enough for heavy turning operations, you make the shaft over length, 2, and machine off the surplus at Z, 3, using a half centre.

 

  

37. Cutting Special Gaskets
Aug 15, 2016

With a car which is old, of unusual make, or which was originally made onlv in small numbers, it is sometimes necessary to renew a damages cylinder head gasket, and it may happen that no gasket is available commercially. The same difficulty arises if it is desired slightly to raises if it is desired slightly to raise compression on some engines without taking the irrevocable step of machining the cylinder head, when a special thin gasket is not available.A temporary replacement, a sort of “get-you-home’’ solution, can be provided by a gasket cut from a sheet of thin Hallite. Using a ball-ended hammer, hole positions, waterways, combustion chambers, can be marked on the sheet which is laid on the cylinder head. Cutting out is done with punches and wood chisels on a block. The head should be well pulled down on assembly and again when the engine has warmed up. On an engine of modest compression ratio, and which is not driven hard, such a gasket can have a life of a few hundred miles or even one or two thousand miles; but in most case, it eventually burns or blows through between two cylinders-for it is without the copper sheathing which protects the asbestos interior of the normal gasket.

 

 

Cutting Special Gaskets

 

 

A much better gasket, whether needed because no other is available, or for modest tuning, can be made from sheet copper, 1/32 in. to 3/64 in. thick. With this there are problems of production, for punching and hammering, which are likely to distort, stretch or thin the sheeting locally, cannot be safety employed, and drilling of any but small holes is risky.In making such a gasket, experience suggests that the holes for holding bolts or studs should be produced by a hand-operated cutter, rather than by drilling. The other openings should be marked and cut with a saw file, or made by careful small-hole chain-drilling and filed to templates .The set-up for producing the holes can be as at A, using a cutter as at B. the copper sheeting for the gasket, slightly larger than the head all round, should be clamped firmly to it with wood. Where the holes are to be cut, the backing should be a flat steel bar held by clamps and a valve spring compressor. This last has a forked end, so the end of the adjustable stop on the cutter can abut to the cylinder head.

 

When two or three holes covered by the steel bar have been cut, it can be moved (tighter with the wood). But burrs left by the cutting tool should be filed off, and cut marks arranged so as not to come immediately under other holes.The silver steel cutter, turned to enter the head holes, should be drilled for the shank and bored at the end to about 3/64 in. wall thickness. Three or four teeth can be filed, and a cross-hole drilled and countersunk for a rivet. Tempering should be to dark straw colour after hardening. Shank and handle should have a fine thread to secure by locknuts. If the thread is 26 t. p. i. (cycle rate), the advance per turn is 0.038 in.; and eight holes in the flange of the stop provide adjustment steps for successive cuts of just under 0.005 in: which is about correct. Thus, a cut can be taken, the stop re-set, and another taken. Faster adjustment than by a screw in the flange of the stop is given by a spring-loaded lever, as at C, where the index holes are cut out to the edge. As holes are made, the wood can be drilled and bolts used for holding. When all holes are finished, a thick cartridge-paper pattern, marked on the head and carefully cut, can be placed on the gasket, and waterways and combustion chambers marked. With a wood backing the size of the gasket-and the two bolted together-these shapes can be saw filed from starting holes. Alternatively, steel part-templates locating from holes, as at D, can be made for chin-drilling and filing. Preferably, there should be a template bolted each side of the gasket which should be on a wood backing with packing wood of suitable thickness, as at E. 

 

 

 

36. Repair Gear Cutting
Jul 29, 2016

In cases of temporary repair to gears, repairs by pegging, or otherwise where only moderate accuracy is required-and speed may be a factor-filing tooth profiles are acceptable methods, using simple contour and spacing gauges. Often, too, pegged teeth can be improved by filling in the curved spaces with soft solder or brazing material, to provide a longer effective contact line. This can reduce noise and shock, with the main strength of the substituted teeth residing in the screwed-in pegs.A higher standard of accuracy in finishing, both in contour and spacing, naturally follows where machining is practicable—either planning, endmilling, or forming with a slotting-type gear cutter, in conjunction with suitable indexing. Nor need this last, even in the absence of dividing means, occasion a problem, for a gear with most of its teeth existing can be used with a simple fixture, and the work performed one lathe, milling machine, or shaper.

 

For a mounting in the lathe chuck, when teeth may be finished by planning with a tool on the slide rest, or when a milling attachment can be mounted on the slide rest, the set-up can comprise a mandrel for the gear, and an arm of flat material for locating andindexing by means of a bolted-on jaw, as at A. The gear should be a push fit on the mandrel turned down to take it, and the bar can be drilled or bored to the same diameter-when a nut at the end will hold all together. Fixing of the arm to prevent movement can be from the lathe bed or stand, or the bench behind it, by removing the gear and turning it.When it is proposed to finish the teeth by end-milling with a cutter running in the lathe chuck, the gear must be mounted on the slide rest or vertical slide. For the slide rest mounting, as at B, the mandrel can be from square stock, and the arm (at A) can then be a plate with a jaw functioning on the same principle. The reaction block for the slide rest clamp can be supply the fixing for the plate; and, as before, indexing can be effected by taking off and turning the gear.

 

 

Repair Gear Cutting

 

Using slotting-type cutterIf the tooth-finishing operation is to be done with a slotting-type gear cutter, the set-up must be on an angle-plate on the vertical slide, with the gear lying flat, and a vertical up-feed bringing it past the cutter running on a mandrel in the chuck-possibly with tailstock support. The principle of clamping and indexing can be similar to that of the two previous mountings-and with appropriate adaptations mountings can be made on shaper or milling machine. Before planning teeth to profile, whether the spaces have been completely filled in or partly produced by sawing and filing a plain slotting operation, as at C1, using tool 2 is advisable to remove surplus material. The cross slide, of course, provides feed, and the saddle the cutting stroke. Subsequent cuts finish the profile as 3 with tool 4-which tool must be tiled to fit the teeth, given clearance, hardened and tempered (or ground), and in use carefully regulated for depth of cut. Lubricant may be helpful on occasion, as can easing of the feed on back strokes. An end-milling cutter, as at D, can be made by turning silver steel rod to profile, filing flats and giving clearance. For improved front rake on the teeth, two grooves X may be grounf along the profile on the blank, followed by backing off through angles Y and giving clearance.The slotting-type gear cutter, as at E, is machined with the profile on its edge: then teeth can be formed and given clearance by sawing and filing.

 

 

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