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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.

 

 

35. Simple Cutter Grinding
Jun 30, 2016

ALTHOUGH it is possible to sharpen circular saws and cutters merely by grinding the front face of each tooth, and although this is the only method possible for some tools, a considerable amount of cutter grinding is nevertheless done on the clearance or relief angles of teeth. It has the merit of sharpening the cutter, while at the same time bringing it circular. In a works, the machine employed is a universal grinder or a tool-and-cutter grinder. The exceptions to this method of grinding for sharpening are tools with complicated profiles, like taps and circular gear cutters. To sharpen these the only practicable method is to grind the front faces of the teeth. In the case of a tap, grinding the profile for sharpening, even if possible, would reduce the diameter and the thread produced would be too tight. But for a circular saw, a slitting cutter, or a roller mill, the loss of diameter is of no importance. Grinding on the top face or clearance angle of each tooth has the advantage of bringing the cutter circular, so that in use the work is evenly spread over all the teeth. In some instances if the cutter is not carefully ground or the mandrel on which it is mounted wobbles this does not occur. Then there is a type of rhythmic cutting with vibration, and the finished surface is irregular or full of chatter marks.

 

Simple Cutter Grinding

 

 

 

The principle of grinding on the clearance angles of teeth is as at A. A cup-type grinding wheel may be used and the cutter mounted on a mandrel, free to turn in bearings or a bracket. A support is arranged for the tooth being ground; and the cutter is simply held by hand to the support and traversed past the grinding wheel. When a tooth has been ground, the cutter is turned to the next one without altering the feed. Naturally, the height of the cutter and of its support are such that the required angles is ground on each tooth. Where a grinder is not available, a lathe can be used on this principle, running the grinding wheel on a mandrel in the chuck and fixing a support strip on a block bolted to the lathe bed. For the cutter, a simple mandrel can be attached to the vertical slide which will provide the means of height adjustment. Cut can be put on from the leadscrew feed to the saddle, while traverse will be from the cross feed.An end mill may be sharpened in this fashion, as at B, showing a method of mounting a small mill by its parallel shank in a simple jig on the vertical slide when a lathe is used. Such a jig may be made by boring a hole for the mill shank in a block of material like aluminium, and fixing a support strip by screws.

 

 

A collar each side if the block locates the mill, while permitting rotation from tooth to tooth. For a larger shell mill, as at C, a mandrel must be provided to mount in the jig, though the principle is the same.Spiral teeth as on a lawnmower rotor or a wide roller mill, can be sharpened on lathe set-ups. With any spiral tooth cutter, either it or the grinding wheel must be traversed, while the cutter is kept down to the support strip-so that it turns slightly in grinding a tooth.To grind a lawnmower rotor, one end of the spindle can be held m the chuck, the other supported by the tailstock. Using a portable grinder the support strip must be arranged on the saddle below the wheel, as at D. Each tooth or blade, is then kept down to the support as the saddles is traversed. To grind a roller mill, grinding wheel and support are as at A, with the mill mounted on a simple jig, as at E. This is on the vertical slide, cross-wide over the bed. The mill is then merely held down to the support strip and pushed along the mandrel past the grinding wheel.

 

 

With its capacity to grip firmly or apply steady pressure, the vice holds the solution to a variety of production problem in the small workshop, where it is frequently necessary to adapt equipment and technique that in a large workshop would require jigs or press tools can often be performed with special jaws or other means in the ordinary vice. One ever-present problem is to grip the work firmly without marking it from rough jaws; another is the problem of holding small parts in a relatively large vice. There are easy solutions to both. Apart from the normal slip-on pads or soft jaws which can be used to protect work, it is often sufficient to hold the work in cardboard like a piece of cigarette packet. Being thin and backed closely by the metal jaws, this gives a firmer grip on work than thick fibre jaws. Strips of metal, such as aluminums and brass wood, and all sorts of soft materials, can be used in the same way. If the major part of work is machined or likely to suffer damage from standard vice jaws, a pair of smooth-faced ones from mild steel will turn the bench vice, for this purpose, into a fixed machine vice.

 

Vise Jaws for Special Purposes

 

 

At times, too, it is convenient to hold a machine vice by its base in the bench vice, using the machine vice for mounting the work; and on this principle, special small vices, or pin vices, and even toolmakers clamps, can be mounted for small work. Mild steel pads, as at A, adapted to features of components, enable them to be held safely and firmly when even soft jaws would be ineffective. They may be components like unions or plugs with external threads, or merely standard screws, for which the pads are drilled and tapped at their centre line and then eased on their faces to grip. Small-diameter or thin-walled tubing can be held in plain holds; and by countersinking the tops of holes, countersunk rivets can be made from rod. Typical operations using such pads are as at B. A snap-head rivet (1) can be made from rod. Gripping it in the pads with a suitable amount proiecting and forming it with a punch. This is made in the usual way from silver steel rod, dimpling its end with a drill, and rounding the cavity with a steel ball and a blow from a hammer. Hardening and tempering should follow if the punch is to be in frequent use. A countersunk rivet (2) is made by beating the end of the rod into the countersink and filing the surplus off. Tubing (3) – after annealing by heating to red and plunging in water if it is copper or brass – is flared with a taper punch. Matched to a coned union, such a flared end makes a short – length pipe fitting. A simple pressing operation is performed in dowelled jaws, as at C. It is to squeeze on the clip which secures a flexible hose to its union. Initially, the clip is a ring of annealed brass, which is slipped on the hose. Then the union is pushed in-its entering stem having a nozzle end or serrations; and a squeeze in the jaws completes the job. Usually the radii for them can be intelligently judged.

 

A half-clip, as at D, can be finished in jaws as in the upper diagram. Two centre-line drilling are made to produce the radii in the jaws-one for the radius of the rod, the other for the outside radius of the clip; and the face of this jaw is cut back to the thickness of the clip. If required, prior shaping can be done in jaws as in the lower diagram. Flanges can be produced on sheet metal discs, squeezing between a strong ring or washer ring or washer and a centre plug of suitable size; while flanges on straight edged can be formed by beating over flat or rectangular material. Using strip material. Using strip material, light angles can be made in this way-and these made into channels at a second beating, as at E. For shearing operations (preferably using an old vice) jaws can be made as at F, with a cast steel chisel and narrow anvil. 

 

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