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GARAGE AND WORKSHOP NOTES.

31st August 1926, Page 63
31st August 1926
Page 63
Page 63, 31st August 1926 — GARAGE AND WORKSHOP NOTES.
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Useful Contributions from our Driver and Mechanic Readers.

Facilitating Screw-cutting.

AVERY ingenious device for attachment to lathes while cutting screws is sent us by "E.M.," of Glasgow, aud we think that this should commend itself not only to all those who have to cut screws, but also to the makers of screw-cutting lathes.

The mechanic will find this well worth his trouble to make, especially if his lathe be not fitted with a saddle dial, and the time spent in making will be saved on the,first metric thread he has to cut.

Briefly, the attachment consists of two strikers which complete a circuit with a small battery and an electric bell and give audible warning that the leading screw is in position to be engaged. You will understand the advantages of this even in ordinary screw-cutting. When cutting a screw, of which the number of threads per inch is divisible by two but not by four, and the lathe has a four threads per inch leading screw, the nut is in position to engage every second turn of the screw.

The usual method is to mark the chuck and leading screw and engage when these two marks coincide, and the machine must he run slowly enough for the eye to follow these marks. If the nut be wrongly engaged the job, and possibly the tool, will we spoiled.

The task is difficult and slower with odd threads and even more so with metric. In fact, when setting up for metric threads on an English-pitch lathe, the machine must be moved by inches at every cut to ensure that the tool has its proper start.

With this fitting even a 6 min. thread can be cut as easily as a 1-in. pitch one.

The lathe is set in the ordinary way, the two strikers are set to coincide with their respective contacts, in which position the bell rings, the strikers are secured and the lathe started.

It follows, therefore, that only when these strikers return to the set position will the hell ring, and this is the moment for the leading screw to engage. The operator is thus left free to mind his tool and transverse feed, for he hfts no dial or marks to watch and he can run the machine as fast as the tool will cut.

In actual practice it is seldom necessary to alter the position of the strikers or cams. When the bell rings, put a gentle pressure on the engagement lever and let the nut drop in when the screw comes round.

The accompanying sketch shows the fittings suitable for most machines, but details can be altered to suit any particular type.

For instance, a small round-head setscrew, fitted to the stop collar on the lathe spindle will do just as well as the cam ring shown on sketch, as this striker never requires adjustment.

The device consists of two strikers„One fitted to the lathe spindle, on or adjacent to the stop collar, anti the other to any convenient part of the leading screw. A fibre pad is mounted on a piece : . of flat spring steel (an old gramophone motor spring can be cut to suit), which is secured at one end to a hard-wood or fibre block, the other end having a contact piece fitted like an ordinary coil blade.

The contact piece registers with a brass contact screw, which is continued through the block and ends in a terminal nut (A).

The fibre block is secured to a quadrant lever, which must be insulated from the contacts and blade, and the whole is secured to the headstock of the lathe, provision being made for adjustment by means of a thumbscrew.

A piece of suitably shaped spring steel, carrying a terminal nut (B), is secured to the lathe bed in such a manner that it is insulated therefrom and clear of the body of the leading screw cam ring, only the point of the cam making contact.

An insulated wire is connected from B to the contact screw (A) in the block. Another wire is connected from the securing bolt (C) of the coil blade to an electric bell and thence_ to the battery. The other pole of the battery is connected to the lathe bed (E).

The spindle cam, pressing on the fibre 'pad, makes a connection between A and C, the leading screw cam makes a connection between E and A, thus complet-ing the circuit and causing the bell to ring.

To try it out, set the lathe in the ordinary way, but instead of putting chalk marks on the chuck and leading screw, set the two cams to register one with the fibre pad and the other with the spring contact piece on the lathe bed, Raise the quadrant lever until the coil blade makes a connection. In this position the bell will ring.

As the circuit is complete only when the two cams are in this position, this is the moment when the leading screw should be engaged. It follows that even when the leading screw is revolving at almost the same speed as the spindle the bell will ring only when the screw is in the correct position.

A Front-axle Repair.

FORTUNATELY for lorry drivers a broken front axle is a trouble that has not often to be dealt with in modern vehicles of good make, but should such a thing happen it is as well to know how to get home with such aid as may be found in a local blacksmith's shop.

"D. McCI.," of Isle of Gist, makes u suggestion which he has found to answer in such a case; he uses a clip to hold the broken parts together. but, fortunately for him, the axle on his vehicle broke with a long oblique fracture, so that he was able to hold the parts together by one clip only.

Axles, however, seldom break in this manner, the fracture usually being more like that shown in our illustration. In such a ease the single clip he used would not unite the broken parts.

Acting on his suggestion, however, we illustrate a clip that has been found very useful for the purpose. It consists of two pieces of stout iron, such as that used for cart tyres, and which every blacksmith keeps in stock. These are laid on the,top and under the axle, and plates with holes punched while hot by the blacksmith are used to hold them together by means of ordinary bolts.

We have known such an emergency repair to last during quite a lung journey home, but should a very long distance be unavoidable we should advise 'fitting four idates.

Controlling Hacksaw Penetration.

THE hint illustrated is so simple that it hardly requires further description. Any strip of metal—an old blade will do —can be clamped against the saw to form a depth gauge, and to limit the depth of the cut, where many cuts have to be made of the same depth. "

of Bath, is the originator of this hint. 1345

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Locations: Bath, Glasgow

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