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Moving the Table

FOR the other cuts lower the table 0.011 each time, and revolve the cam one division until the highest point of the cam is reached, then raise the table 0.011 for each division of the cam.

When the cam comes from the milling machine there will be found to be small grooves left between the cuts. These may be easily removed by smoothing off with a file without impairing the accuracy of the cam.

Most screw-machine cams can be made in this manner, and they will be found to be more accurate than if laid out and filed to the line, and also much easier to make after one has become accustomed to the method.

MILLING CAMS BY GEARING UP THE

DIVIDING HEAD

By the method here shown, cams of any rise may be milled with the gears regularly furnished with the milling-machine.

Lead-of-Cam

Angle of Elevation

of Index Head

Lead for which Milling Machine is Geared

FIG. 5. Diagram for Angle of Index Head

With the head set vertically the lead of the cam would be the same as the lead for which the machine is geared, while with the head horizontal and the milling spindle also, a concentric arc, or rest, would be milled on the cam, regardless of how the machine was geared. By inclining the head and milling spindle, we can produce any lead on the cam less than that for which the machine is geared.

The method of finding the inclination at which to set the index head is shown in Fig. 5, and is simply the solution of a plain rightangled triangle, in which the hypothenuse represents the lead of the machine, and one of the other sides represents the lead we wish to produce on the cam. By dividing the latter by the former we get the sine of the angle of inclination.

Take for illustration a plate cam having 3-inch rise in 300 degrees.

360
300

= 0.15,

which is the lead we want on the cam, while the slowest lead for which the B & S. machine can be geared is 0.67

0.15

= 0.224.

Consulting a table of sines, we find 0.224 approximates closely the sine of 13 degrees, which is the angle at which to set the head, and if the milling spindle is also set at the same angle, the edge of the cam will be parallel with the shaft on which it is to run. Fig. 6 shows a milling-machine set for this job.

When a cam has several lobes of different leads, we gear the machine up for a lead somewhat longer than the longest one called for in that cam, and then all the different lobes can be milled with the one setting of gears, by simply altering the inclination of head and milling spindle for each different lead on the cam.

If the diameter of the cam and the inclination of the head will admit, it is better to mill on the under side of the cam, as that brings the mill and the table nearer together and thus increases rigidity, besides enabling us to easily see any lines that may be laid out on the flat face of the cam. Also the chips do not accumulate on the work.

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FIG. 6. Dividing Head Set for Cam Milling

The work is fed against the cutter by turning the index crank, and on coming back for another cut we turn the handle of the millingmachine table. As a result the work will recede from the cutter before the cam blank commences to turn, owing to back lash in the gears, thus preventing the cutter from dragging over the work while running back.

In this way we use to advantage what is ordinarily considered a defect in machine construction.

The milling-machine, when used as shown in Fig. 6, will be found to be more rigid than when the head is set in the vertical position, and the cams will work more smoothly on account of the shearing action of the cutter.

One possible objection to the method here advocated is the necessity of using, in some cases, an end mill of extra length of tooth. In practise, an end mill 3-inch diameter and with a 3-inch length of tooth is not unusual; but the results in both speed and quality will be found entirely satisfactory.

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TABLE OF PITCHES AND APPROXIMATE ANGLES FOR CUTTING SPIRALS ON THE UNIVERSAL

MILLING MACHINE

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[graphic]

TABLE OF PITCHES AND APPROXIMATE ANGLES FOR CUTTING SPIRALS ON THE UNIVERSAL

MILLING MACHINE

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