Albert Graham

Many, many times have models of inventions and machinery fallen wofully short of the acme of perfection indicated by the general finish of every other part, in those insignificant little key-ways and splines which are so deficient when put in with a cold chisel or file.

It is not often possible, from a monetary standpoint, for an amateur to possess a milling machine, and even those that are fitted to be attached to a small lathe often cost from $60 to $75, which is nearly as much as that of the lathe.

But it is possible for the amateur to construct a small machine out of ordinary materials that will do the work very well indeed. Of course gears cannot be cut on it, but small keyways, grooves in flat pieces and heads of screws, and squares on the end of circular rods or screws may be readily cut. It is to be understood that this is not intended to do the heavy work that a regular milling machine will do, for the power which can be applied is small and the feed can at best be but slow, but it will do the work intended far more rapidly than can be done by hand methods.

The base a, Figs. 1 and 2, is made of well seasoned maple glued together on edge. While the glue is setting, be sure that the strips are tightly clamped together. Several pins should be driven through from side to side to prevent the pieces slipping past each other when the pressure of the clamp is applied. This can be readily accomplished by boring 1/4 in. holes through each piece, using the first one as a guide, and threading the strips on 1/4 in. dowels. When thoroughly dry remove the clamps and plane the pieces to a true surface on each side, and making the whole at least 1 in. thick by three wide. This method of construction has the advantage of preventing warping.

The guides b are made of the same material, planed perfectly straight and secured to the base, a, by several screws placed about two inches apart. If preferred, one strip may be glued fast and the other left free for adjustment in case of under wear. The angle between the base and the inside of the guide strip is 60°. If this work has been well done, a firm, solid base will be the the result, which will last a long time, as maple is a very hard wood of close grain, and after being well seasoned does not warp out of shape. It also has great strength.

The housings c are made of two 1/4 in. pieces of maple glued together by the strip d and pivoted to the base by the through bolt, e. The circular slot f permits the cutter to be raised or lowered at will, while another through bolt g serves to clamp it fast. The cutter arbor runs in bearings at the upper end, as shown. Each housing is armored with a brass plate h which is secured thereto by small screws. The plate takes the crushing force of the through bolt g and prevents the washer under the nut from marring the wood. It also adds greater strength and stiffness to the housings, and the arbor passing through the holes in the brass plates that just fit, enables the strain to be transmitted in a direct line to the clamping bolt g.

The arbor k is turned from a piece of 3/4 in. ma chine steel. An enlarged section in Fig. 4 shows the bearings afforded for the cutter. The cutter is clamped against the shoulder by means of a nut I, which is provided with a fine thread, say about 30 to the inch. The cutter being driven by a small key, this nut has merely to hold it against a shoulder and can, therefore, be made very light. By this construction the arbor is kept very stiff, upon which fact depends the smoothness of the cut. Two collars, m m, are fitted to the arbor and are adjustable, being fixed in position by the set screws shown. This provides adjustment in the direction of the arbor axis. The crank should be at least six inches long, and if the amateur so desires a flv-wheel may be added to insure steady motion.

The bearings for this arbor are made of Babbitt metal, which is very hard, and can be melted and run around the arbor when the latter is set in place, exactly parallel with the base. The bearings will then be in line and need no further work excepting the drilling of an oil hole from the top. The hole for the Babbitt metal should be countersunk from either side, and if the brass plate is tinned on the inside the bearing will be soldered to it and make a very stiff construction. When it is necessary to remove the cutter, either to sharpen it or replace it with another, the collar m is loosened and the arbor drawn through the bearings sufficiently to allow space between the smaller and adjoining housing, through which the cutter is removed.

The V block n should be made of some metal on account of the strain put upon it by the clamps in holding a piece. It may be made of either cast iron or brass, the latter being better on account of its greater toughness and ductility. The piece is small and does not permit large bosses for the clamping screws. The V may be finished with a file to a very true surface, which can he determined by laying a small mandrel in it after the surface of the mandrel has been covered with a thin layer of red lead. The high spots will be covered with the red lead, while the lower portions will not touch it at all. By repeated dressings and trials a very fair V may be made. The bottom of the V block should be filed perfectly true with the upper surface of the mandrel when it is lying in the groove. This will insure the cut being of uniform depth. Fasten this V to the wooden slide o by several screws passing through from the under side. A few small clamps should be made of steel to hold the pieces which are being cut, as shown at p.

This V, which is really the table of the machine, is fed along the guides by means of the screw 5, which bears against a collar secured to the end of the block o. This screw has a groove cut in its end, as shown at t, which allows a horseshoe shaped slot to pass over it and thus permits the table to be fed in either direction. This arrangement is more fully shown in the small sketch directly above. This feed screw works through a threaded hole in the iron or brass plate V fastened to the end of the base a. A three or four inch handle should be fitted over a square on the end to provide sufficient leverage for feeding, as when the cutter is taking even a rather small chip the pressure against this screw is very great. The threads should be very much finer in pitch than ordinarily used on a 3/8 in. screw. About thirty to the inch will give a fairly fine feed and will not require too long a time to return the table after the cut is made. The handle is made a free fit on a squared end to enable its removal in case a very long rod is being splined, in which event, the overhanging end would prevent the handle making an entire revolution. This screw may be operated by the left hand, while the right turns the cutter.

To extend the value of this machine a small vise is provided, as shown at Fig. 3, which fastens to the V by the screws similar to the one used for the clamps. The pieces w w are made of 1/2 in. square steel, either machinery or tool, the latter being preferable on account of its ability to to be hardened, and these jaws should be hardened if possible. The screws x x are simply 5/19 in. square-headed cap screws. A small V is filed in the centre of each jaw to enable it to hold small screws and cylindrical pieces while the cutter is working on their heads or ends. By providing another boss on the side of the table V, the vise may be swung around until the jaws are parallel with the direction of feed, which is often of great advantage.

The making of cutters is not a very difficult operation. The blanks are turned to size in the lathe, the teeth filed in the periphery by hand and then hardened and tempered., Do not let the fact that the spacing may not be regular worry you in the least, for it is better that they should have irregular teeth ; a cutter with regular teeth will chatter if it is given the slightest excuse,, whereas an irregular spacing will tend to obviate this tendency, owing to the inability of the succeeding teeth to drop into the furrow made by the advancing or cutting tooth. This action is exactly similar to that which always occurs in a file of regular cut. Files are now generally made with an irreglar spacing which, although not readily determined by the eye, prevents that an- . noying chatter with its consequent rippled surface.

These drawings have not been dimensioned, but a ' scale has been laid down from which the measurements may be taken off. This allows the amateur to alter the machine to suit his particular needs if it should not serve as designed. The cutter and section of the arbor is just double the scale to which the machine is drawn.

Do not attempt to use cutters of much larger diameter than 1 1/4 in., as you will not have power to drive them with your arm. Neither will the machine stand up under a cutter much over 1/4 in. in width, but it has been designed to do the ordinary run of work generally pursued by the amateur, the object in view being to give him something that will do the work and that can be built at a very low cost without the use of more than one casting, which is extremely simple to make and requires no core work.