Albert Graham

A "fat" spark is desired to insure regular ignition, and to avoid "misfiring," a trouble frequently met In the operation of gas engines, but which may be almost entirely avoided if care be taken to see that all parts are in good working order, and correctly adjusted. For engines of comparatively small size, the length of spark which can be produced from a coil is not so important as that the spark shall be full or strong enough to affect ignition with regularity. The coil here described, if carefully made, will be found adequate for this purpose. It is about the size rated as a half-inch spark coil. A vibrator is shown, but can be dispensed with under certain conditions.

The dimensions of the several parts are as follows: Length of core 5 inches

Diameter of core 5-8 ,,

Guage of core wire 20 Guage

Primary coil, two layers No. 16, C. C. M. W. Secondary coil, 1 pound ,, 34, C. C. M. W.

Condenser, 40 sheets foil, 4 x 5 inches Condenser, 60 ,, paper, 6 x 8 inches To make the core, cut into 5" lengths, enough soft iron wire, 20 guage to make a round bundle |" diameter; about 150 pieces being the required number. It is quite necessary that they be very soft. If doubt exists on this point, wrap some binding wire around the bundle and put in the fire, allowing it to remain over night, taking it out in the morning when a new fire is made. Then clean and rebind and after dipping the ends in solder so as to secure a solid end, remove the binding wire, file the ends smooth, and soak in paraffin. This may be kept fluid if a hot water bath is used. Do not heat on the fire in a single vessel, as it may possibly ignite when so heated.

Procure or make a round paper tube, 5-8" inside diameter 5" long and about 1-16" thick, mailing tube of the right size will answer. Coat well with spirits shellac and then insert the wire core; the ends of the latter should project about 1-16" on the hammer end. The primary coil is then wound in two layers upon the inside of this tube, No. 16 single cotton covered magnet wire being used. Leave about 6" of wire free at the ends for connections. This coil is 4" long. Coat each layer with spirit shellac, which makes a good insulation. The outside diameter of this coil will be about |". A piece of thick hard rubber or fibre tubing 1 |" inside diameter is then placed over the primary coil. To the ends of this tubing fit square ends A of hard rubber or wood i" thick. If wood is used give it several coatings of spirit shellac, paying particular attention to the joint between the ends and the tube. The ends should be 4" apart, inside measurements. From the top side of one end drill a 1-16" hole which will just open at the lower inner side close to the tube. The end of the wire for the secondary coil is put through this hole from the inside, with a short length projecting for connections. Before doing this, however, increase the thickness of the tube at the ends about 1-8" with several layers of thin bond paper, coating each and binding same with shellac. Be sure to keep the opening clear to the hole in the end for the secondary wire.

The secondary coil can then be wound, after testing the wire with a galvonometer to ascertain that there are no breaks. In winding also, constantly examine the wire, to locate poorly insulated, bent or broken places which would cause trouble and perhaps spoil the action of the coil. As each layer of the secondary is wound, baste well with paraffin applied with a small, flat brush. Before winding the final layer, put on a single thickness of thin, smooth bond writing paper, and then wind the final layer, the paper giving a smooth, even finish to it. The end of the wire is put through a hole drilled in the other end piece, leaving end for for connections.

The vibrator, if one is used, is made as follows: - The hammer head h is cut with a hack saw from a piece of round annealed bar iron, and is 2/3" diameter and 1/4" thick. It is finished smooth on the faces with a file, then fastened with two minute screws to the piece of spring brass s, which is 1 3/4" long, 1/2" wide and about No. 26 guage. The other end of the spring is fastened by a machine screw to the foot L, cut out of a piece of bar brass. This is 1-2" on the base, §" high and 1/2" wide. A hole is tapped in the base for the screw holding it to the stand, and also for the tension regulator t. This regulator is made by drilling the end of a knurled head, machine screw and forcing in a piece of brass wire. The post p is a piece of round, brass rod 1/4" diameter and 1 |" long. The lower end is tapped for a screw to hold it to the base, a washer being placed under the head of the screw, and at the top and directly in line with the centre of the hammer for the contact screw C. This screw should have a knurled head, and the point tipped with a bit of platinum. The point of contact at the back of the hammer should also have a piece of platinum soldered to it. To solder on the platinum heat the part, place a drop of melted solder and allow it to cool enough to see if the solder holds, then warm with blow pipe until fluid and place the piece of plat inum in it and cool. The vibrator should be so located and adjusted that the hammer will, when the coil is in operation, vibrate so rapidly as to make a distinct buzzing.

The condenser is made as follows: - Forty sheets of thin tin foil are cut 4" x 5". Sixty sheets of thin wax paper are cut 6" x 7". Lay a piece of smooth writing paper on a smooth surface, lay on a piece of the wax paper, then a piece of the foil, with the end overlaping the paper 1/2", then another piece of wax paper. Another piece of the foil is then laid on but this time overlaping on the left end. Follow with alternate layers of paper and foil, the ends of the latter projecting alternately on either end, until all the sheets of foil have been used. Examine the paper carefully, rejecting any sheets with holes. If suitable wax paper cannot be purchased, soak thin bond writing paper in paraffin, and smooth with a warm flat iron, interposing a sheet of ordinary paper between the iron and wax paper. Every few layers press with a flat-iron.

The overlaping ends of foil are soldered together with soft solder as follows: - First bring all the ends together with a slight turn, which may be done by pressing them over a small round rod about 1/4" diameter. Trim all the ends even and fasten together at two or three places by punching a hole and binding with a fine copper wire. Make a V shaped trough from a strip of sheet iron, closing the ends with putty. Fill this trough to the depth of about 3-16" with the molden solder, and put one end of the condenser into it and and let harden. It must not be too hot otherwise the foil will melt away from the sheets. If well done, all the sheets will be connected with the solder, to which attach the connecting wires with a drop of solder.

As previously mentioned, a vibrator is not used by some gas engine builders, one fat spark being preferred, if the timing can be accurately adjusted, to the less strong, but more numerous sparks caused by the vibrator. The writer has had no personal experience with a coil without a virbator, so cannot say how satisfactory a working can thus be obtained. Perhaps some of the readers of this magazine can give information on this point.