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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.

 

58. Collet Chuck Fittings
Aug 01, 2017

THE main advantages of collet chucks, over other types, are the firmness and the accuracy with which small diameters are held. It is why the normal equipment of instrument lathes and precision lathes includes sets of collet chucks covering ranges of standard sizes. Work and tools rods, drills, spindles and cutters can all be set up without difficulty.Production lathes which are used for repetition machining of small components from barstock, are also fitted with collet chucks; and many toolroom lathes have them as standard or as additional equipment. When lathes are not fitted with cullet chucks, other means of holding work and tools must often be contrived-like split bushes, or halved blocks which can be gripped in jaw chucks; or split mandrels with taper threads at the nose ends which can be closed by ring nuts. All these are satisfactory for one-off jobs or for short runs of several components. Within their limits, they equal cullet chucks and show the advantages these have over other types. Often from such an example comes the determination to fit the lathe with a proper set of collet chucks-when time permits. For the project is seen as one involving a considerable amount of precision work. This is true if one goes about the job in the usual way: but by following the method described here, the result is the same for practical purposes, with much less time and effort expended. The idea is to use a holder for collets in a small., four-jaw independent chuck, in which it can be quickly set to run truly. The holder can be in mild steel, left normal, or casehardened. Alternatively, cast steel can be used, unhardened-or hardened, then tempered to dark-straw colour.

 

Collet Chuck Fittings

 

 

In each case, treatment is to choice. If the lathe has a hollow spindle, the holder can be as at A, with a parallel diameter to grip in the chuck, a shoulder to abut to the jaws, and a reduced nose end which can be set true by indicator. In machining, important work should be left until the chucking diameter is finished and the material has been rechucked nose’ end outwards. This end is reduced, faced and centred. Then a drill is run through the material, followed by a boring tool-and a reamer if to hand. After this, the bore is opened for a short distance, then the end is tapered with the topslide at 15 deg. If the holder is hardened, grinding and lapping operations follow. At their front ends collets are tapered to suit the holder; and their rear ends are threaded so that each will take a sleeve into which is screwed the drawbolt passing through the lathe spindle. Pulling on the drawbolt by a nut or a handwheel draws the collet into the holder. Collets can be in good mild steel, and much work can be avoided by using bolts, left normal, or casehardened. Using a bolt, it is set true at the neck in the independent chuck, as at B. With the topslide at 15 deg., the head is machined to angle V.

 

 

If the collet is to be hollow, the bolt is reversed in the chuck and centred and drilled from the back. Otherwise, it goes straight into the holder to finish the front end for the job. Centred from the tailstock, it is drilled, then reamed or bored, according to circumstances. Then it is cross-drilled and slit. If rod is used, the collet can be turned and threaded on a set-up as at C. If the lathe has a solid spindle, a holder for collets must be as at D , threaded for a nut, through which the nose of the collets can extend. Screws WX and a plate should be fitted, as collets sometimes stick. Then they can be easily loosened. Outside machining or grinding operations can be done at any time to a holder on a mandrel as at E; and collets can be slit in a pair of blocks as at F. For boring, the blocks are held in the independent chuck; to form a slot, their faces are filed. In use, the blocks are gripped in the vice at positions YZ. 

 

 

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