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10.Bending And Forming
Aug 14, 2015

NUMBEROUS bending and forming operations can be performed in the vice with a hammer and simple mandrels and formers. From round rod can be made hooks, eyes, special staples, chain links; flat sheet or strip serves for light-section angles, channels, boxes and endplates. Small diameters and thin sections can be worked cold but for manipulating large sections using mild steel, a concentrated form of heating is desirable – such as a welding torch – which brings the metal to bright red heat. Heating prevents cracking in hard steels and some types of iron are prone to cracking if bent when cold. Cracking is also prevented in copper and brass sheet by annealing; this is performed by heating the material to red and plunging it in water. Some materials may tend to crack when bent in one plane and not when bent at right angles. Hard brass and copper, common iron and duralumin are most prone to cracking when working. The first and second should be annealed, the third worked at bright red heat and the last avoided except, for large-radii bends or when heat treatment is possible.

 

Bending And Forming

 

 

Forming an Eye

From wire, an eye can be turned on a piece of rod A using round-nosed pliers, but diameters of about 1/8 in. or over require the assistance of the vice. A mandrel from a piece of mild steel rod is then utilized; it is gripped in the vice with the rod B. It is convenient for the mandrel to be provided with a flat one side, filed for the vice jaw to grip; on the opposite side there can be a shallow groove at an angle to locate the rod to be used for the eye. This groove can be cut with a small round file. At the second stage of the work C, the end of the rod X is pulled against the edge of the vice to form the neck; the end Y is then carried round the mandrel to form the eye, as at D. Removed from the vice, the rod is tapped down the mandrel, the surplus cut off and the eye straightened by squeezing in the vice. E and F show the flat and the groove on the mandrel, while these may not be absolutely necessary, they do prevent movement while working. If produced cold, the eye will spring open slightly when pressure is released on the end of the rod Y. Consequently, a mandrel somewhat smaller than the finished inside diameter of the eye is required. At red heat, however, close-fitting eyes can be produced from mild steel rod.  

 

How To Bend And Form 

 

 

Links and Tee Handles

 

Chain links and tee handles G can be turned using simple holders. For the first stage H, a hole can be drilled through a piece of bar to take the rod, the end of the hole radiused if necessary. For the second stage, a split holder Z can be made by drilling at the joint of two pieces of bar. Cut to form jaws, they can be gripped about the rod for the second turn of a chain link and utilized as at J for the third turn forming a tee handle.

 

 

Channels and Flanges  

 

Short angle lengths in strip metal can be hammered over the vice jaws but for long lengths the strip should be held between two lengths of angle iron K, gripped one end in the vice and the other fixed with a clamp. When an angle is formed, a channel L can be produced over a suitable section piece of bar. For turning thin, ductile sheet metal and strip, hardwood formers of oak or beech should be made to the inside dimensions required, as for the metal box at M. A piece of bar should be clamped on the opposite side of the sheet metal, level with the block where the corner is to be turned- this prevents buckling as the metal is turned over. Round flanged ends, as for small boilers, can be formed from copper discs held between two suitable large washers N and squeezed in a powerful vice. The discs should be annealed before hand; forming can be assisted part of the way through the operation by hammering over the smaller of the washers. 

While it is often possible to drill holes over-depth from the tailstock, then face the material to length for accuracy, there are occasions when it is desirable or necessary for the drilling itself to be accurately performed. This is true also of counterboring and cutting angular seatings for which fine control of axial movement is essential. For ordinary work, there are various ways and means of exercising depth control. A pencil mark can be put on the drill, or a nick made on it with the corner of a grinding wheel. The extension of the tailstock barrel can be measured – from the end or from a scribed line or centre punch dot or inside calipers or dividers can be used from the tailstock to a mark on the barrel. These suffice for the occasional job on which better than usual accuracy is required, though for a succession of such jobs, it is a convenience for the means of control to be built into the tailstock in the form of a graduated barrel or a micrometer collar. Then not only is there control for precision work, but for ordinary work there is a check on progress with control over depth clearance, so that bar stock is not wasted in facing out unwanted holes in subsequent use. A graduated barrel for a tailstock can be arranged as at A, with spacing of graduations to choice, 1/32 in. being a normal minimum. Reading should be at a pointer rather than at the end of the tailstock, as the advance to a particular graduation can be seen, and there is no temptation to go beyond to be certain of not under-drilling. Such a pointer can be cut from sheet material, bent, drilled and fixed by screws to the tailstock. 

How To Do Tailstock Feed Control

 

 

On a screwcutting lathe, the tailstock barrel can be graduated with a set-up as at B. Holding a piece of rod in the chuck, it is machined from the topslide to the taper in the tailstock barrel to form a mandrel on which the barrel can be mounted, leaving clearance from the chuck jaws to work the vee-tool. The handle and key are removed and the barrel allowed to turn in the tailstock body. To mark the base line, the vee-tool is mounted sideways and drawn along the barrel by saddle feed. Then to cut the graduations, with the tool in the normal attitude, the lathe is set to the required thread (say, 32 t.p.i.), and the chuck turned by hand, the tool being fed in at the line and drawn out after a given rotational movement. For uniformity, simple block gauges can be used between a chuck jaw and the bed. Minimum helix angle follows from a fine thread, even though graduations may be more than one turn apart. Figuring can be applied through punches, and burrs eased off with a smooth file. On some tailstocks, a graduated or micrometer collar can be arranged as at C. They are tailstocks on which the rear boss can be machined true on the outside for the collar to fit to a shoulder, and be driven by a pin let into a spoke of the handwheel. Total graduations for a true micrometer collar must agree with the thread on the barrel (125 for 8 t.p.i., and 100 for 10 t.p.i.), though fewer will give accuracy to ordinary fractions.

 

 

A set-up as at D admits of machining the outside of the boss on the tailstock, using a bar through it. Driven from the chuck, this can be flattened at the end for bolting on blocks for the tool, which can be lossened and tapped down for depth of cut. Feed follows from lightly clamping the tailstock to the bed and moving it along with the saddle. The collar can be turned and bored from bar stock or a casting and set up for graduating as at E. For this, its bore can be a force fit on the mandrel which mounts the change gear and is supported by the fixed steady. Later it can be bored to fit the tailstock. Indexing of the gear can be done as at F with a bar bolted to the lathe bed, and a sliding jaw in the teeth of the gear.

 

08.Tips For Tapping
Aug 02, 2015

Perhaps the greatest cause of tap breakage is excessive pressure applied at an angle to the axis of the hole. It is also the cause of the hole being out of alignment. Some time ago I had to tap a number of 2 BA holes about 1/2 in. apart and fix lengths of screwed rod. The plate was about 3/16 in. thick and when finished the spaces between the rods were anything but parallel. This incident, together with two broken taps, was the origin of the following device, designed to eliminate tap breakage when turning back to clear the tap. It also acts as a guide to ensure the tapping pressure is evenly applied, and controls the feed.

 

Construction is simplicity itself. Only ordinary straight turning is needed if a solid bar is available. Alternatively two pieces of pipe welded together and turned to fit can be used but this seems somewhat clumsy. A 5 in. length of 1 3/4 in. dia. Shafting or b.m.s. round is – chucked in the three – jaw and turned down to 1 in. dia. for 3 3/4 in. in length. With fixed steady supporting the 1 in. dia. end, the bar is bored through with a 1/4 in. or 3/16 in.dia. long reach drill using high speed and plenty of lubricant. Don’t forget, especially when drilling holes of abnormal depth, to ease back the drill many time s to clear the flutes – unless, of course, the swarf is ejecting continuously. The hole is opened up in stages to 11/16 in. dia. Check the diameter of the tapholder and if necessary open out to a slide fit. The tapholder shown is the Eclipse No 143. Reverse the bar in the chuck and turn a recess to suitable depth and diameter to fit the drill chuck, i.e. dimensions A and B. This should be a firm non-sloppy fit over the nose of the chuck.

 

Tips For Tapping

 

Next, either mill a 1 1/32 in. wide slot in each side of the barrel or make one by drilling through, cutting up with the hacksaw and finishing with a file, to allow the cross-bar to pass through. This slot will enable the tapholder to slide downwards as the threading proceeds. For the smaller size Eclipse No 43 holder for 11/16 in. barrel dia., bore or drill out to 1/2 in., and for the length of slot 2 1/2 in. (see diagram), substitute 1 1/2 in. The rest of the dimensions can be scaled down to suit. The compression spring should be fairly stiff for this size holder but weaker for the No 43 size, i.e. BA and 3/16 in. whit and below. The length of the spring should be such that in its normal length it should allow the cross-bar to be about 1/2 in. from the open end of the slot. The diameter of the spring should be a free fit inside the bore of the barrel. Although primarily designed for use with a drill press, if the work is too large to be accommodated it is easy to rig up a suitable jig. A plain turned spigot could replace the chuck. This could be clamped to the work or bench. However, with the drill press, the work already drilled to correct tapping size is located and bolted or clamped to the table and either packed up, or the drill head lowered until the tap engages the hole and the spring in the barrel becomes slightly compressed. The cross-bar is then turned and the gadget takes care of the rest. The drill remains stationary, except, of course, that the chuck revolves with the rotation of the cross-bar and tapholder.  


 

Every once in a while your three-jaw chuck will tighten up suddenly at one or more spots, and you are faced with the job of taking it apart to clean out the swarf. I have found that plugging the hole in the centre of the chuck with a small sponge ball, is a great help in keeping out the swarf. It must, of course, be taken out when you have a rod through the hollow spindle, but usually it can be left in for 75 per cent of the time, which is a tremendous help. I use only half a ball. I take a sharp knife and smear a drop of oil on it and cut the ball down the middle. If you cannot buy a ball which will push in tight after being cut in half, trim away the thin edges with a sharp knife, again using a smear of oil to help.  

07.Simple Milling Cutters
Jul 12, 2015

For a large number of milling operations, as performed by the amateur in the lathe when rate of production is not important, simple cutters contrived at very small cost in the workshop provide results equal to those obtaining from bought tools. It is not, of course, essential to employ multi-tooth or multi-blade cutters for many milling and similar operations. With care, and by regulating the speed and feed, the same work can often be done with a single-point tool. In production work, multi-cutting-edges permit of a high rate of feed; and wear is distributed over all the cutting edges – which together mean faster production and longer runs on set-ups.


Simple Milling Cutters


For facing operations in production work, a large end mill or slab face cutter would be used; but in lathe milling, a single-point cutter or tool as used for turning can be employed. If the surface is small, a tool off-set in the independent chuck is all that is required; and such a tool will also cut a slot. If the surface is large, however, a holder is necessary for the tool, this being mounted in the independent chuck. In such an event, an improved double-blade cutter can be made, as at A, where a piece of rectangular mild steel has been drilled (and, if possible, reamed) to take two round tools held by grub screws. True setting in the chuck with the cutter tips rotating in the same plane can be easily checked by allowing the tips to scrape past a fixed bar on the slide or other mounting. Should the setting be incorrect, the holder can then be tapped or packed as required; and the cutters can be adjusted by the chuck jaws to spin on the same circle. A preliminary check for projection of the cutters from the holder can be made by laying this on its back-on a surface plate, and using a surface gauge or height gauge, over the butter tips.

 

 

For milling soft materials like aluminium or brass, cutters of silver steel, hardened and tempered, are satisfactory; but for cast iron and steel, cutters can be made from short pieces of round high-speed or alloy steel tools. For milling hollow surfaces or radii, a single-point tool set in a mandrel can be used, as at B. The mandrel should be driven by holding one end in the chuck and supporting the other at the tailstock, since a set-up between centres driving the mandrel by a carrier is too choppy and chatter-inducing. A double-edged cutter can used on this set-up, checked for length over its tips and set centrally in the mandrel. Small end cutters for narrow slots in work can be made from silver steel, as at C. The piece of rod should be turned to the diameter, X, of the cutter. Then the diameter is filed to rectangular section backed off behind the cutting sides; and the end face is backed off oppositely to form a pair of cutting edges. The tool is hardened and tempered in the normal way and should be run at fairly high speed with light cuts. A bought slotting cutter or saw needs to be mounted on a mandrel, as at D, where there is a driving pin fitting in the keyway, and the sleeve holding the cutter up to the shoulder is slotted to fit over the driving pin. As distinct from saws, slotting cutters may be built up mild-steel holder, as at E and F. Four or more cutters or tools may be used, clamped by grubscrews or setscrews, the tools being flattened on the sides if required. Grooved cotters, however, admit of a narrower holder and avoid the need for tapped holes. The holes for the cutters having been drilled, they should be temporarily plugged (pieces left projecting for removal), then the cotter holes can be easily drilled through the holder. 

06.Pre-loading Bearings
Jul 08, 2015

THE principle of torque in tightening is of considerable importance in modern machine and component assemblies employing special ball or taper roller bearings in opposition. The spindles or mandrels of lathes, milling machines and other tools may incorporate such bearings, which are now also standard for pinion shafts and differential carriers in rear axles of cars. The torque required to turn the lathe spindle or the pinion shaft of the axle is often called pre-load, and given in lb. in. It represents largely the load above ordinary friction applied to the bearings in assembly. That is, if the bearings were assembled just without play, they would be subject to friction and require a little torque for turning. But by pre-loading, a noticeable and specified increase in torque is made. 

 

Pre-loading Bearings

 

 

 

Pre-load, however, can be established in another way. When bearings are assembled just without play, a reference measurement can be made over them endwise. Then it can be arranged to bring them together some small pre-determined amount (say, 0.002 in.), and this is the pre-load, though naturally it has the effect of increasing the torque required to turn the shaft, as the principle is the same as before. Pre-load - as determined by bearing and component manufacturers – needs to be reasonably correct. Otherwise if too heavy, there can be resistance, overheating, and possibly early wear of the bearings; while if not pre-loaded enough, a lathe spindle, for example, would run loose and be subject to chatter, and a car rear axle would whine on drive or over-run. In addition to this torque (usually a small figure in lb. in.) to turn the shaft, the nut or nuts on the shaft may be given a spanner tightening torque as a very considerable figure in lb. ft. Clearly, this is important, too, for tightening of the nuts brings the bearings together, and can thus affect the other torque or pre-load. It must not be overlooked that pre-load specified refers only to the bearings, so it cannot be tested while the shaft, or the gear at its end, is engaged in any way. If an oil seal is fitted it must not be in place for checking pre-load unless the manufacturer has specially allowed for it. Again, two figures may be given for pre-load, a high one for new bearings and a low one for new bearings and a low one for bearings that have been run-in. These must not be confused with two figures together showing limits of pre-load, such as 3 to 4 lb. in. Here, a torque of 3 lb. in. should not turn the shaft, while one of 4 lb. in. should be capable of rotating it. At A and B are examples of pinion shaft assemblies with taper roller bearings. At A drive is taken from an outside flange, and there is an oil seal which must have been allowed for in the pre-load or be absent when testing. 

 

 

The bearing outer members are separated by shoulders in the casing, and the inner members are spaced by a sleeve, at the end of which shims normally allow for adjustment. If a test shows insufficient pre-load, the shaft is removed to extract one or more of them. At B bearing outer members are separated as before, but there is no spacing sleeve, and locknuts, usually with washers, admit of applying pre-load. The splined end of the shaft is enclosed, taking the drive through a sleeve from the propeller shaft. Testing of the pre-load can be done with a rod length X through the shaft, pulling on it at right-angles with a spring balance. Length X in inches X balance reading in pounds = load in lb. in. For a shaft with a flange, a sheet metal drum can be made to bolt on as at C, and a cord wrapped round and a weight applied as at D. Then radius Y in inches X weight in pounds = pre-load in lb. in. 

05.Facing And Countersinking
Jun 15, 2015

In other than small sizes it is generally advisable for spot or facing cutters to be provided with more than two teeth. For when, say, four or six teeth are operating at once cutting is smoother and there is far less likelihood of chatter or digging in occurring. Of course, two cutting edges are convenient on a spot facing cutter with a spigot or guide to enter the hole in the work, because cutter and guide can be solid, yet the teeth are easily filed. With several teeth, however, it is otherwise, since the spigot offers an obstruction to filing. Hence, constructions are necessary in which cutter and spigot are separate.Two common constructions are as A. In the upper cutter the spigot and cutter shank are one piece, unhardened, the shank being threaded to screw into the cutter, which can be of silver steel, drilled and tapped, provided with filed teeth, then hardened and tempered. In the lower cutter, the spigot is a small separate piece, short, tight-fitting mild-steel or silver-steel rod, unhardened, while the cutter and shank are of silver steel, hardened and tempered. Coned countersinks for screws can be made in either of these ways. 

Facing and Contersinking

 

 

 

Another Solution :   

On occasion the screw-on cutter provides a solution to the problem of back-facing behind a lug or inside a component where there is obstruction to normal application. The threaded shank is put through the hole, the cutter screwed on to it, and the tool pulled back into the work instead of pushed, as it is rotated in drill or brace. Flat and coned cutters of this type, B, are provided with teeth facing the opposite way to normal, owing to the reverse direction of rotation. The bore for the threaded shank should be plain to just beyond tooth depth, since with the thread to the end of the teeth, there is danger of breakage when the shank pulls in tightly. Pliers may hold the cutter for unscrewing, or spanner flats can be provided. On either flat or coned cutters, teeth, C, can be provided with small three-cornered files. These should be used tilted off-square for the cutter teeth to be deeper on the outside than at the centre – in which way, the files are kept clear of the cutting edges on the opposite side. For this work the cutter can be held on the top of the vice jaws, screwed on a piece of rod. Cleaning and sharpening after hardening can be performed with three-cornered hones or abrasive slips.

 

 

Tongue and Pin Drives :  

A tongue formed on a machined shank or a pin put through a plain shank are alternative means to threads for providing drive to cutters. The latter then have plain holes for pushing tightly on the shanks. On a machined shank, C, the spigot or guide is turned leaving a substantial boss or shoulder. Then the driving tongue is formed by filing down each side beyond the spigot. The backs of the cutters are file-slotted to engage on the tongue. On a plain shank a removable cross-pin can be provided, D, and the back of the cutter again slotted – either entirely by filing or by drilling a hole and filing down into it to leave a rounded bottom. On a coned cutter, E (left), a removable spigot, X, can be employed to control depth of countersinking if a piece of flat metal is placed beneath the work and care observed that chips do not get beneath the spigot – a method ensuring rapid and uniform countersinks without danger of marking top surfaces. Rapidity is also a feature of setting up a cross-pin drive cutter for truing internal faces or bosses, E, the cutter being placed inside the work, the shank entered and the driving pin fitted. Back-facing, such as in a tube to leave the bore clear when countersunk screws are fitted, can be performed as F, with a screw-on cutter like the coned type at B. The tricky operation of drilling a shank at an angle to take an inserted cutter can be easily performed as G. A steel collar is fitted on the spigot, cut at an angle for starting the drill, and held to the shank in a vice using a distance piece if necessary. 

 

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