match-safes and similar articles, and for this work the best lubricant to use on the tools is naphtha or crude oil. A mixture of crude oil and vaseline also is good. However, the naphtha will be found the best, as it will not affect the satiny finish around the edges. Besides the use of a proper lubricant when engraving aluminum, considerable skill is necessary in the making and use of the cutting-tool. A tool made similar to a turning tool for aluminum, finished to a sharp, keen point with lots of clearance, will work excellently.

A property that makes pure aluminum very valuable for many purposes lies in its ability to withstand the action of acids. While the metal is easily affected by alkalies, the strongest acids do not injure it to any noticeable extent-in fact, acid acts on it in much the same manner as on platinum. For parts of apparatus which have to be immersed in strong acids for considerable periods, parts of aluminum will prove highly efficient. One use to which the metal has been put in this respect is for hooks for removing photographic negatives from the acid baths. Acid funnels of aluminum also have proved a boon to many.

SOLDERING ALUMINUM.

The last, but not by any means the least valuable, process in the working and use of aluminum is soldering. To many the difficulties experienced in this line have proven a great detriment to the successful use of the metal for many purposes. The uncertainty as to the best solder to use has been one. There are any number of solders which have proved fairly successful when skill has been employed in using them. The following has proven to be the best in practice for soldering the pure metal or any of its alloys: Fuse together one pound of block tin, four ounces of spelter, two ounces of pure lead, three pounds of phosphor tin. With benzin clean all dirt and grease from the surfaces of the parts to be soldered and then apply the solder with a heated copper "iron." When the melted solder covers the surfaces completely, scratch through it with a wire brush, which will break the oxide and take it up. Spread the solder again with the iron and allow to cool. When it is found necessary to "sweat" aluminum parts together, first clean the surfaces

as described for soldering, then heat the parts until the solder flows freely over them, scratch through with the wire brush, wipe with clean waste, and clamp together. A first-class joint will result.

ALUMINUM AS AN ABRASIVE.

Aluminum, despite its metallic character, can be used as an abrasive for sharpening knives. It has the structure of a delicately grained stone, and under friction gives an extremely fine mass which adheres powerfully to steel. Consequently, blades sharpened on aluminum rapidly take a thin, sharp edge which cannot be produced by the best stones. If knives are passed with utmost care over a razor stone, the edge, when magnified 1,000 times, shows irregularity and toughness, while edges produced on aluminum, when submitted to the same examination, appear perfectly straight and smooth.

CHAPTER XXXII.

Hints, Kinks, Ways, and Methods of Use to Toolmakers and Die-makers.

NOTES ON CIRCULAR FORMING TOOLS.

WHEN making circular forming tools always keep the fact in mind that the diameter has much to do with their wearing qualities; and that unless their diameter is proportionate to the diameter of the work satisfactory results will be hard to obtain.

In Fig. 572 are shown two circular tools of 1 and 2 inches diameter, respectively, both cut out inch below centre, as they would be if intended to operate on the front side of the machine

:

FIG. 572.

or at the back side with the work running backward. Although shown in this position, the principle involved is of course the same as though the tools were placed the other side up, the toolpost being bored out above the centre-bore of work spindle, instead of below, as in the case referred to.

Referring to Fig. 572 it is easy to see that the cutting-edge of the larger tool would have much greater endurance than that of the smaller, the rake or clearance of the latter being excessive. This difference of rake in circular cutters must of course increase with the difference in diameter of the cutters, provided the cutting-edges are located at the same distance from centre. The case is similar to that in Fig. 573, where are shown side by

side two straight cutting-off tools, the clearance of one ground as at E and the other as at F. The angle of clearance of Ris practically the same as that of the larger circular tool in Fig.

F
E

FIG. 573.

574, while that of F coincides with that of the smaller tool and shows much less durability than the tool ground as at E.

It is usually the best practice in making tools for a certain size machine to keep them as closely to one diameter as possible. In the larger machines cut out the tool inch from centre, and of course bore the tool-post a corresponding amount above or below the centre, according to which side up the tool is to be

a

FIG. 574.

operated. For the smaller machines make the tools of less diameter, cutting them out inch from centre and boring the post to correspond. In Fig. 574 line A B represents centre of work, CD centre of large cutter, showing the same cut inch below centre, while CD represents centre of small cutter and shows the same cut inch below centre. The clearance of both cutters is practically identical.

A KINK FOR DRAWN WORK.

A sharp corner under a shoulder or flange is often a very desirable thing, and one generally considered impossible in drawn

work because of the necessity of a round corner on the die to keep the metal from tearing while being drawn through the die. There is a method, however, of doing this that is quite successful, as shown by the accompanying sketch, and it seems to be about the only way it can be done. The "kink" consists in making the punch a series of steps as per Fig. 575, with round corners instead of a parallel one, as in the usual practice; the steps to be about as far apart as the depth to be drawn; and the difference in diameter of steps to be determined by thickness of stock. The blank, instead of being a round disk, is a washer, the outer edges held not too tightly by the usual pressure ring or plate, and the end of the punch to be a little larger than the hole in the washer.

The

punch will open the hole to the full diameter of the end and turn the sharp corner of the disk in the most surprising manner. The steps follow each other rapidly, each one enlarging the hole to its own size and carrying the stock down through the die, the last step being the finished size of the interior of work, and the hole in the dies being the outside diameter of same. A die like this needs a press with a good long stroke, depending, of course, upon the character of the work.

BRASS-WORKING TOOLS AND THEIR USE.

Figs. 576 to 583 illustrate brass-working tools for hand work. No. 576 is a flat planishing tool which is used for finish