Page:Popular Science Monthly Volume 91.djvu/964

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��Popular Science Monthly

��How to make a Secure Joint in Copper Tubing

^INCE copper tubing is so useful in O radio work, knowledge of how to make a neat and ef- fective joint should be valu- able. In build- ing helices • or spirals it is im- possible to splice short pieces in the or- dinary way. By tapping threads inside each of the abutting ends and inserting a short threaded piece of copper or brass rod to fit, as in Fig. i;* a perfect joint may be made. Where a wire extension from the end of the tube is desired, the same general plan may be followed, as shown in Fig. 2 of the illustration. — F. Mac Murphy.

���A threaded plug in the pipe ends for a close joint

��Things to Know About Lubricants for Machinery

ALL machinery owners have had it drummed into them that only a good grade of mineral oil is fit for oiling their machinery; but there are a few extreme cases in which something else is used, and they are interesting enough to mention. The function of a lubricant is to supply a thin film between the sliding metal parts so that they do not touch each other with sufficient pressure to produce friction or heat or to cut one into the other, and to keep the sliding parts cool.

The "bearing pressure," or pressure of one part upon the other, determines to a great extent the kind or quality of lubricat- ing oil to use; for with heavy pressure a poor or thin oil will squeeze out, or its film become broken down. Then the metal parts will rub and heating and cutting will begin, to the detriment of the machinery.

As a cooling medium, water will be found satisfactory. Where pressures are light and a flood or bath of water can be maintained without causing rusting, water is fully as satisfactory as oil and much cheaper, al- though the instances where it may be used are not many.

The garage man finds a great deal of trouble caused by carbon in the cylinders — pre-ignition, knocking, loss of power, etc. This carbon is considered a necessary evil,

��of no good whatever. But experience shows that a certain quantity of this carbon — not an excess — is as good a lubricant as may be found. For sleeve-valve motors it has been found that if a carbon deposit is in the grooves and creases of the sleeves no other lubrication is needed. This is easy to believe when we know that carbon is a constituent of mineral oil. Such a deposit is a form of graphite, which we know is self lubricating. Therefore it is a substitute for grease.

I Pure glycerine is as good a lubricant as any oil if used where there . is no great amount of heat. It will stand almost any ordinary bearing pressure and has a high viscosity rating. In plants manufacturing food products, bottling plants and brew- eries, compressed air is used extensively in contact with the products for various pur- poses, such as charging, filling, etc., and there is always a certain amount of the lubricant from the cylinder of the air- compressor that finds its way through the pipes and comes in contact with the prod- uct. In almost all cases this would be dis- astrous if ordinary lubricating oil were used, owing to the discoloring, the various chemical actions and the possible injury to health. But for this purpose glycerine is extensively used.

Fish oils, vegetable oils, animal oils and sometimes kerosene are used for such machinery. We find the various vegetable oils used on machinery in the preparation of products where a single drop of mineral oil on, or in, the product would be decidedly harmful.

Thus, for instance, a machine working on corn products is lubricated with corn oil and the operator is supplied with a squirt can filled with this oil. None of the vege- table or animal oils, however, is to be rec- ommended for lubricating any metal sur- face. They are for use only in extreme cases where the bearing pressure is low. The bearings should be carefully attended to and watched.

A mixture of lard oil and kerosene will make a sufficiently free-running journal and is often used on hand-operated feed tables of machines. When freshly applied it gives a free and easy sliding fit to roller- bearings, but owing to the evaporation of the kerosene and the gumming quality of the lard oil, it must be renewed and fresh- ened up frequently. Soap is the best lubri- cant to use on wood, and soapy water makes the best lubricant for rubber surfaces.

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