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64. Useful Tool Grinding Jig
Nov 26, 2017

THE object of this article is to enable the model engineer to produce accurate flat faces on the tool-faces which can be struck again instantly on a regrind. Perhaps its first recommendation is that it can be produced by anyone possessing a 3& in. lathe. Next, in order of merit, is that it can be produced from scrap.As a matter of expediency the prototype has been built up from aluminium alloy angles and plate, and for this reason, perhaps, the scantlings are on the heavy side. In steel, all thicknesses, with the possible exception of the top plate, could be reduced, but this is a matter of individual taste. Any grinding jig can, of course,‘be offered up to the wheel at any unusual angle, but usually an alteration in the angular inclination entails a consequent shift towards, or away from, the wheel face if safe and efficient support is to be given to the tip of the tool. The next most desirable feature of the appliance is that it can be secured permanently to the bench, with the edge of the top table no more than just clear of the wheel. The top table rolls round an axis coincident with its front edge-protractor markings on one side angle enabling it to be set at any desired angle within its scope. The addition of another protractor on the top plate enables the operator to carry out double angle grinding. Not all tools may be ground with equal facility, of course, but with the aid of a few simple accessories, any normal tool can be precision ground as to front and side clearance and side rake. This category would include right- and left-hand knife tools, roughing tools with flat faces, screw cutting and parting tools. Round-nose tools with a common clearance at front and sides may also be ground by using the top table alone, set to the appropriate angle.

 

Useful Tool Grinding Jig

 

 

The jig illustrated is used at the side of the wheel and it is possible that modification to the guard may be necessary to accommodate it. It is essentially intended for tool finishing and would, therefore, be set up to the fine wheel of a double-ended grinder. When forming a new tool from a stock bit, the roughing-out is done by hand on the coarse wheel. The angle is tested from time to time by touching it to the fine wheel with the jig set to the appropriate angles-the final grind is done on the fine wheel, of course. Once established, the tool angles can be struck again at any time. The setting of the jig and the grinding of a normally blunted tool is a matter of seconds; honing, too, is reduced to the minimum

 

The table top

For this a slab of plate h in. x 104 in. x 4 in. is required. It should be flattened to a straightedge to reduce filing or machining. It is then cut to shape using hacksaw and file. The centre recess on the front edge is made to accommodate the nut and washer securing the wheel. It is not really necessary to machine the top face but it should be smooth and flat to promote easy manipulation of the protractor guide. A groove, & in. wide x { in. deep is machined in the top face to accommodate the guide bar. This can be done by setting up the plate on angle plates secured to the cross slide with the centre line of the groove at lathe centre height-a & in. end mill in the S.C. chuck is employed.

 

It is unlikely that the full length of the groove can be machined at one setting as few slides on small lathes have the necessary travel, but a careful resetting will enable this operation to be completed. That part of the inner edge of the plate remaining after it is gapped for the wheel nut must be beveled to an included angle of 60 deg. or slightly less. Later it will be necessary to cut two small notches in the outer edge & in. wide x & in. deep to give passage to the trunnion bearing flange when the angularity of the top table approaches the maximum.

 

The sole plate

This is a simple rectangular piece of plate which can be made by hacksaw and file. It should be reasonably flat otherwise it may distort when screwed down to the bench and tend to jam the trunnions. If the wheel is the full 8 in. dia., a recess in the upper surface will need to be cut. Holes for the holding down screws are left to individual requirements.

 

 

 

Top trunnions

It will be seen that the bearing edges of these are machined to a radius struck from a centre outside their surfaces. They are formed from 24 in. x 24 in. x fin. angle bar, each 2# in. long. The outside faces of the flanges should be checked for 91, deg. angularity and corrected if necessary.The cross-sectional edges should be squared off to assist setting-up for machining. For the purpose of roughing out the radii, a tin or card template may be used with advantage for marking out ; the surplus is then readily removed with a hacksaw.

Before setting up for machining, guide lines (Fig. 1) are lightly marked on the facedate-these fix the positio& o$ the edges of the angle bars. With the scribing block on the lathe bed. scribe the first mark + in. yor the finished thickness bf the top plate)

above the lathe centre, carrying the line right across the faceplate. Now turn the mandrel through 90 deg. so that this first line is vertical to the shears.

 

Scribing the location lines

Scribe two further lines (Nos. 2 and 3), 7132 in. above and below the lathe centre. These are the locating lines for the inner edges of the right- and left-hand trunnion angles. The sketch shows how these lines appear when completed. Return the mandrel to its original position and bolt on the angle plate with its heel edge set to the line, in the lower back quadrant. Secure the right-hand trunnions to the angle plate, taking care that its outer flange overhangs the edge of the angle plate by about $ in. (Fig. 1). The vertical flange of the tnmnions is set parallel to the faceplate with its toe in line with No. 2 line, i.e., 7/32 in. off-centre. In slow back-gear turn this edge until the tool is just touching the toe of the 24 in. edge. The heel of the trunnion should now measure 2; in. (approximately) and the radius about 2% in. The left hand trnnnion should be machined in a similar fashion, but with the angle plate mounted on the faceplate in the lower, front quadrant. If two angle plates are available, both trunnions can be machined in one operation.

 

Cutting the zero line

With a sharp V-pointed tool, the centre line fol the radial slots should be marked + in. from the turned edge; likewise the line which borders the protractor marking 5/32 in. from the edge. With the same tool mounted on its side at lathe centre height a zero line is cut on the face of the trunnion at an angle of 45 deg. Some form of dividing is desirable for cutting in the protractor markings but failing this, a draughtsman’s protractor can be set up with the exercise of a little ingenuity and used as a dividing head with sufficient accuracy for most requirements. Short lines at every degree, with slightly longer ones at the 5 deg. and 10 deg. stations are engraved by feeding in the cross slide for the requisite amount. Figures (& in.) stamped later at every 5 deg. station assist in setting when the jig is in use.

 

 

 

Protractor markings 

It will be noted that protractor markings need be engraved on one trunnion only. The opposite trunnion requires only the centre line for the slot to be marked in at this stage. The slots could be milled in before dismounting by the use of a slide rest mounted milling spindle. Failing this, the slots are drilled out and finished bv filing. Do not omit to bevel the inside edges of the-top flinges to an angle of 60 deg., as shown. In the initial stages the trunnion  bearings should be dealt with. As far as roughing-out is concerned this is done in a similar fashion to their mating angles C, again bearing in mind that there is a left- and a right-hand unit. The angle sections in this instance are 39 in. long.

 

 

 

Setting up trunnion bearings

Again they are set up on the angle plate secured to the faceplate in the settings appropriate for a boring operation. It is possible that the off-set required may tax the faceplate beyond its capacity, in which case the work piece could be mounted with its inner surface to the angle plate (Fig. 2), due allowance being made for flange thickness if the angle plate has to be reversed. For this operation, the lines inscribed on the faceplate are 1 and 2, 3% in. above and below centre height and 3 25132 in. to the left of centre. Machining is carried on with a boring tool until its point is just scraping the toe of the flange as before. It is a wise plan to check the radius produced, as the operation approaches completion by using the mating trunnion as a gauge. A smear of blue on the bearing edge of the latter will indicate progress and machining should be stopped when the two surfaces are shown to be mating. A touch with a scraper at the bench should then ensure smooth action between the two parts.

 

Clamp assemblies

The shapes of these 8 in. plates are identical, but, on assembly, they need to be handed to right and left, therefore the securing studs must be screwed through the plate to suit. No. 2 B.A. clear holes are drilled and countersunk. The clamp plates, secured to the trunnion angles in the correct setting, are used as jigs for marking off the tapped holes in the bearing angles. It is wise to lock the clamp plates in position with the studs at the extreme ends of the slots-this precaution enables the table to be returned to zero without checking when in use. With the trunnions and bearings and clamp plates assembled after drilling 2 B.A. clear holes in the top and base flanges, they are secured to the table top and sole plate in turn for drilling the tapped holes in the latter paas. The setting should be carried out with maximum care for, as will be realised, the set-up is now the equivalent of a shaft rolling in a bearing.

 

 

 

Ensuring smooth working

If the trunnions are not axially true in their bearings the smooth working of the apparatus will be destroyed for the same reason that a bent shaft will not turn in a bearing. To prevent this, the trunnion and bearing angles should be secured temporarily to the top and sole plates by means of clamps. When the desired freedom of working is ensured the holes are marked off, or drilled by using the angles as jigs.

With the fastening screws in place, the main unit is substantially complete. It is almost certain that packing will be needed to bring the surface of the top plate reasonably into line with the centre of the stone. A slab of seasoned hard wood should be chosen and bedded to the bench top to avoid rockobviously the top surface of the packing should make an exact right angle with the side of the stone.

 

 

 

Nuts for holding down

For the purpose of holding down, & in. square nuts may be sunk into the under surface of the packing before the latter is screwed down to the bench-the holding down screws then screw in from the top. The holes for these through the packing should be drilled a little oversize to give some latitude to the setting of the jig.

 

Top plate protractor guide

The drawing is self explanatory and the only difhculty is the marking of the scale. Here again, in the absence of dividing apparatus, a draughtsman’s protractor can be made-to serve. A special mark should be made at 278 deg. on either side of the zero line, thus being half-the-angle of Whitw-orth screwcutting tools. For the sake of stiffness the guide strip which engages in the groove in the top plate should be of steel. It should bear on the bottom of the groove and the top surface should stand a thou. or two proud of the surface of the top plate A. This ensures that the clamp will hold it securely without distortion. Needless to say, the strip should be. a sliding fit in the groove. The remaining accessories, the extension guide (G), the square (H) and the “ boat ” (J) are simple and easy to make. The G-clamp can be bought for a shilling or so at any tool dealers.

 

 

 

 

 

 

Guide is left floating

The protractor is used for all normal, simple tools such as right- and left-hand knife tools, roughing and parting tools and, in fact, any tool which has flat facets which do not deviate too far from the zero angle. In grinding the tools mentioned, the protractor guide is left floating and is worked to and fro with one hand along the groove, while the tool is nresented to the stone with the other hand, so distributing the wear on the latter as far as possible. It will be noted that if the angle of the tool is too acute, the influence of the guiding edge of the protractor is lost, particularly on short tools. Tool-holder and boring-bar bits, for example, are not easy to align with the protractor swung round to a large angle. In this circumstance, the extension guide (G) is brought into use. The protractor is set to the desired angle and fixed at a suitable station on the top plate by means of the G-clamp. The extension guide is laid along the edge of the protractor with one end near to the stone, thus supplying the necessary guiding edge to the short tool

 

 

 

Making it a short interlude

The square will be found necessary when grinding acute angles, which operation is illustrated in the sketch. It is also used when grinding the top faces of tools with the table set to give the necessary side rake and the protractor set for zero, positive or negative back rake, the latter being necessary when grinding certain tool-holder bits, particularly those for screw cutting in a Jones and Shipman tool holder, for example. The boat (J) is used for underlining tools such as planer and shaper tools. A little preliminary practice with the apparatus will transform the chore of tool grinding into nothing more than a very short interlude in the more serious business of getting on with the job, as well as removing the question of tool angles from the realms of guesswork.

 

 

 

63. Tips For Tapping
Nov 14, 2017

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.

 

Tips For Tapping

 

 

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 1/4in. 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 times 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 tap holder and if necessary open out to a slide fit. The tap holder 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.

 

Next, either mill a 1 l/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 tap holder 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 crossbar and tap holder

 

 

THIS device represents a method of lathe tool height adjustment and though I do not claim originality, I cannot recall having seen the idea published before. I have been using this tool holder nearly seven years, and it has not given me the slightest trouble. In fact, it has saved me considerable time in tool setting. The holder itself is simply an improvement on the Drummond split toolbox type, which clamps to a pillar, cast integral with the top slide. This pillar on my lathe has a 1/2 in. Whit. tapped hole in the centre about I 1/2in. deep-for what reason I am not sure unless it was for holding the slide in a jig, the pillar having been turned first while the vee-slides were machined. However, I thought that the tapped hole could be used for tool height setting, so the improved tool holder was evolved.

 

Would not reach centre  

The original toolbox had a square hole for the tool, which, when using a right- or left-hand cranked tool, meant bringing the cross-slide well out or turning the box almost through 90 deg. I did not like this at all. And when the toolbox was set with the square hole parallel to the bed for boring and the cross-slide was screwed in as far as it would go, the toolbox would not reach the centre unless I took off the whole top slide and put it in the farthest tee-slot.So I decided to make a new one with screw-height adjustment,, and which would reach the centre without the necessity to change to another tee slot.

 

A Height Adjusting Toolpost

 

 

 

 

The modified toolbox is made out of a block of cast steel, but cast iron would do just as well. The split bush is made of mild steel and the ring of holes under the bolt head is for turning back the clamping-bolt should there be any thread stretching, thus the nut handle is always about 45 deg. off vertical. The drawing will show how simple the adjustments are. Personally, I do not like any tool holders in which the front and top rake angles are altered so as to obtain dead centre. This improved tool holder is only adaptable at present to the My ford Drummond,but it would be easy to fasten a 1 1/4 in. dia. pillar either with a square flange or shouldered and screwed with a fine thread to many existing lathes. I am surprised that this simple holder has not been thought of before. I can assure readers that it is quite solid when taking very heavy cuts.   

 

 

61. Adapting a Telescope
Oct 10, 2017

ALMOST any small telescope can be converted to a microscope by the fitting of a microscope objective, or the lens of a small camera, in place of the field lens. An ordinary telescope consists of a large field lens and a Ramsden ocular. After adaptation it can be used on the lathe and for work on the bench. The best for the lathe is an elbow telescope. It has the advantage that it will stand firmly on the bed or the slotted cross-slide; and you can look into it vertically, in a natural attitude, as in setting cutting tools. Briefly, it makes an ideal instrument when it is fitted with an objective and an optical micrometer-details of which I have given in recent articles. Scribed lines can be set “ spot on ” to the spindle axis by normal adjustment of work in the independent chuck and on the faceplate. My elbow telescope, which is shown in diagram A, was obtained from Charles Frank Limited of 67-75 Saltmarket, Glasgow Cl, a firm with which I have no connection except as a completely satisfied customer. It is a Government surplus instrument, apparently unused, with everything to make conversion as simple and cheap as possible. Perhaps the designer was himself a modeling enthusiast who foresaw its peacetime use. And its use is not confined to small lathes. The massive but handy design should meet the requirements of most production turners. This was my impression when I first examined it.

 

Adapting a Telescope

 

It comprises a well-proportioned gunmetal casting, with a base 5) in. dia., and a lens tube making the total length 8 in. The horizontal line of sight is turned vertically by a prism past a graticule into a Ramsden ocular, which you can adjust by rotating a large knurled sleeve, so that the cross-lines of the graticule are brought into focus. You make the adjustment before using the instrument on the lathe, and afterwards move it towards the headstock to focus the lines scribed on the work. Both sets of lines are then clearly seen-and by adjusting the optical micrometer and the work, you obtain the precise setting. The rise-to-centre from base to lens tube is 1.365 in., which makes possible a cross-slide mounting, with packing, on many lathes. On others, wood blocks can be used to give a centre setting within 1/32 in. The optical micrometer does the rest. In the base, two spot-faced &in. clearance holes, spaced opposite at 4 in. dia., can be used for bolts. Ample space remains for others, or for clamps, though for normal use the instrument stands firmly without fixing. As received, the thing was dustv from long storage, and so I dismantled it with small and mediumsized square-bladed screwdrivers, using a magnifying glass to see the tiny locking screws-whose loss I prevented by doing the work in a tray !

All went well until I came to the field lens. I pulled off a covering sleeve from the tube, took out a tiny locking screw and scraped out a black anti-reflective sealing. Then I had to make a tool as at B to screw out the lens-securing ring. It was from mild steel 1 1/2 in. long X 3/32in. thick. Using the independent chuck, I turned S 3/4 in., T 1 9/32 in., U 1 3/16 in. to 1/16in. deep. I made V 1/32 in. by filing and then casehardened the end. The securing ring

screwed out easily, bringing the field lens with it.

 

 

When you have reached this point, the next step depends on the lens which you intend to substitute, for the holder must be made to suit. For a microscope objective, the holder must have the RMS thread, while a camera lens is best fitted by a flanged holder. Both are shown at C, diagrams 1 and 2. The lens tube of the telescope takes either of them as a split, push-on fitting. The controlling diameter is 1.450 in. on this chuck-and-mandrel work, with brass or duralumin. Diagram D shows the field of the instrument. Line WX is one on the graticle Line YZ is one on the w.ork Having centred the instrument with the optical micrometer, you adjust the work so that the two lines coincide. 

 

 

60. Checking Tapers
Sep 21, 2017

TAPERS are used on many components to hold parts securely together. Examples are crankshafts, spindles, mandrels and axle-shafts carrying flywheels, pulleys, gears and hubs. Wellfitting tapers transmit considerable power (torque) by themselves; but keys are often used for additional security.Machining accurate tapers is a test of skill on the lathe, for the angles must be precise and the finish good. We can correct small errors of angle and faults in the surface by lapping two tapers together with fine grinding paste. But this is essentially a finishing process, and we must not rely on it to correct large errors.For accuracy in machining, the first essential is a sharp tool at centre height and the second a precise setting for the topslide. It happens that the degree markings of topslides are not accurate enough for this setting, and so other methods must be used. Several’ which I have evolved over the yearshave had their merits. Those described here can be used for production work and for one-off jobs.

 

Checking Tapers

 

The gadget shown at A is a taper gauge built up’ from steel washers and studding with nuts. Both washers should have the same outside diameter, so that they can be chucked to set the taper on the topslide. Three or four pieces of studding, or‘ screwrod, can be used, each with four locknuts for adjusting. the washers. These are bored parallel in the chuck, to fit near the larger and the smaller ends of the taper on the shaft. When joined by studding, they make a  lattice gauge, which has the advantage of being adjustable to different angles. Each bore should be machined to a definite size and with a square edge; then the extreme corner should be removed with fine emerycloth. To take a taper from a shaft, the washers are set to fit snugly on the taper and parallel to one another. This you can check with calipers or micrometer, measuring over the length W plus X. The tangent of the half-angle is found by taking the length W as the base of a right-angle triangle and the difference in the radii of the two bores as the vertical. From this relationship, the taper can be found in degrees and minutes’in trigonometrical tables. Hold the gauge in the three-jaw or four-jaw chuck, as at B, with both bores spuming truly, to set the topslide for the inside taper. If the bore is large enough, the cutting edge of the tool should be at centre height. Adjust the slide until the edge of the tool just touches both bores as it is traversed. A dial indicator with a probe attachment can also be used.

 

 

The sketch shows a special dummy electric tool which simplifies the setting. Use a sleeve of insulating material, such as Tufnbl, to mount the too1 in its holder. Two wires Y-Z are connected in circuit with a low-voltage battery and bulb flashlight). When the tip of the toolmakes contact with the bore of one of the washers, the bulb lights up. By noting the light, or Iack of it, as the tool is moved in the washers, you know how to set the slide. To make a check of concentric spinning, turn the chuck with the tool inside one of the washers. On the same principle of two spaced washers, a plug taper gauge can be made as at C, again with the advantage of adjustment. A handle can be machined in mild steel and threaded for the nuts, or a piece of studding can be screwed into a handle. The washers can be mounted and machined in place, their corners being removed with a Swiss file or emerycloth. The effective length for calculating the angle of the taper is like that of the other gauge: total length minus X, to give W. A plug gauge of the same type can be made as at D, with a turned handle, a distance piece, and a single nut at the end. Thin shims to one face of the distance piece give an accurate setting. With the handle chucked and the washers true, you can set the topslide to angle, using an ordinary turning tool. Instead, a diaI indicator can be employed, or an electric device similar to that for the inside setting.

 

 

 

Here is a formula for blackening brass. I learned it in England when I was over last year from Canada and I have found it very satisfactory.

Copper Carbonate . . . . . . 87.5 Grains

0.880 Ammonia . . . . . . . . f Ounce

Rainwater . . . . . . . . . . . . .I 1/2 Ounce 

Heat solution to 175 degrees F and immerse the brass for 30 seconds (or longer). The formula gives a beautiful black brass. It will not take on solder. Rub a soldered joint with stannic chloride using an iron wire brush. The joint will then be brass-plated. For a larger quantity of solution use I lb. Copper Carbonate, I quart 0.880 Ammonia and 3 quarts rainwater. 

 

 

AN experienced model engineer, like a good cook, is a practical person who can often produce acceptable results from odds and ends with few tools. Both may work with equipment which is far from ideal. Until a generation ago, cooks got magnificent results with primitive ovens. Model engineers performed splendid work on elementary lathes. The principle holds today, for it is results that matter in a workshop, as in a kitchen. In some hands_, a fork is as good as an electric whisk, just as in others files and scrapers will do some of the work of machine tools. Recognition of these age-old principles should encourage newcomers; for there are many small tools whose making requires only stock materials and standard screws and bolts,. And the few tools that a beginner possesses for drilling, sawing and filing. The sketches show some examples of tools that can be made with this limited equipment although for some operations a lathe would normally be used.

The first example, shown at A, is a substitute for a toolmaker’s clamp. This clamp is one of the basic tools of a workshop, and is often made as an exercise in technique. In the standard type, there are holes to tap and threads to cut. The heads of the screws are knurled.

 

Tools by Drilling and Filling

 

 

 

In the substitute, these operations are avoided by the drilling of clearance holes and the use of standard screws and nuts. As shown, you drill two clearance holes for the screws in the bottom piece of square bar, and one clearance hole and a dimple in the top piece. If you wish, the ends of the jaws can be hacksawed and filed at an angle. You tighten the clamp with a spanner on the nuts. Diagram B shows clamps that can be used for light work of uniform thickness. Work of this sort often calls for several clamps; besides being large and heavy, toolmakers’ clamps are usually too few in number. For the clamp at Bl, you bend a piece of rectangular steel at right-angles and drill it with the flat piece for the screw and nut. For the clamp at B2, you turn the material U-shape and drill it. This clamp should be squeezed in the vice, so that it has to be opened by pnsmg with a screwdriver to slip on the work. Then there is reduced strain on the screw. The clamp at B3 is made from thick rectangular material, drilled for springiness and slit with a hacksaw. The jaws can be smoothed with a thin file. The tap wrench shown at C is a favourite with some toolmakers. I know professional turners whose preference in lathe carriers is for the type illustrated. Both these tools can be made from square mild steel bar, even by novices. You should clamp the pieces for drilling to keep the holes in line. File matching Vs in the pieces for the tap wrench to locate and grip the tap by two corners of its square. Use a round file to produce shallow radii for work held in the carrier. You can turn each of the handles of the tap wrench in a lathe by holding one end in a four-jaw chuck with the other end centred and supported by the tailstock centre .

 

With three pieces of flat steel 1/16 in. or 3/32in. thick, you can make a gauge, as at D, for checking the angle of lips on a twist drill, to be certain that both are the same. Two pieces are used for the stock and one piece is used for the blade. The stock is spaced by a washer at the opposite end. You can set the blade to a good drill, and then scribe it from the stock, as a guide for resetting on subsequent occasions. Sketch E shows two other easilymade small tools, a depth gauge and a V-block. You make the stock of the depth gauge from two pieces of flat material held by screws; the rod is gripped between them. The two thick pieces for the V-block are spaced by washers on two bolts. A scribing block can be made as at F, with the base drilled for countersunk screws, on which the scribing bar is held by nuts. Make this bar from silver steel, hardened and tempered, or from mild steel, by bending it down and drilling, so that a sewing needle can be held by solder.

 

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