GAGE SETS FOR BRIGGS PIPE AND FITTINGS

THE gages manufactured by the Pratt & Whitney Company for makers and users of pipe and fittings include three distinct sets for each size of pipe, and these are illustrated in Fig. 3. Set No. I consists of a ring and plug conforming in all dimensions to the Briggs standard, and is known as the standard reference set. The plug screws into the ring with faces flush - as indicated by the position of the two gages. The flat milled on the plug shows the depth to which the latter should enter the fitting to allow for screwing up with tongs to make a steam-tight joint; the ring, of course, screws on to the pipe flush with the end.

Set No. 2 the working allowance set consists of the plug already described and a ring whose thickness is equal to the standard ring less the allowance for screwing up the joint. As the plug and ring threads are of the same diameter at the small end, the bottom surfaces come flush when the two members are screwed together. It will be noted that, as the plug enters the fitting only to the bottom of the flat at the side, and the ring screws on to the pipe only far enough to bring the outer face flush with the pipe end, there are a few threads on, or in, the work beyond the reach of the gages; hence with this type of gage a reasonable amount of wear may be permitted at the end of the tap or the mouth of the die without causing the rejection of the work.

The plug and ring in set No. 3 are inspection allowance gages, the ring being the same in all particulars as the standard gage in set No. 1, while the plug is longer than Nos. 1 and 2 by an amount equal to the allowance for screwing up for a tight joint, this extra length being represented by the cylindrical portion at the rear of

the thread cone. When the gages are screwed together the back of the cylindrical section comes flush with the ring face and the threaded end of the plug projects through the ring, as indicated, a distance equal to the length of the cylinder, or the screwing-up allowance. This plug will enter a perfect fitting until the back of the threaded section is flush with the end of the fitting, thus testing the full depth of the tapped thread in the same way that the standard ring gage covers the thread on the pipe end, and at the same time showing that the fitting is tapped to right diameter to allow the joint to screw up properly.

NATIONAL STANDARD HOSE COUPLING

This standard for fire hose couplings was adopted by the National Fire Protection Association May 26, 1905 and has since been approved and adopted by various other organizations.

NOTE: The above to be of the 60-deg. V-thread pattern with one-hundredth inch cut off the top of thread and one-hundredth inch left in the bottom of the 24-inch, 3-inch, and 3-inch couplings, and two hundredths inch in like manner for the 43inch couplings, and with one-quarter inch blank end on male part of coupling in each case; female ends to be cut -inch shorter for endwise clearance. They should also be bored out .03 inch larger in the 24-inch, 3 and 3-inch sizes, and .05 inch larger on the 4-inch size in order to make up easily and without jamming o sticking.

TWIST DRILLS

THE twist-drill is perhaps one of the most efficient tools in use as, although one half is cut away in the flutes, it has a very large cutting surface in proportion to its cross-sectional area. This is made possible by the fact that the work helps to support the drill and the feed pressure on the drill tends to force the point into a cone-shaped hole which centers it.

In addition to the radial relief or backing-off behind the cutting edge, twist-drills have longitudinal clearance by decreasing the diameter from the point toward the shank, varying from .00025 to .0015 per inch of length. This prevents binding and is essential in accurate drilling.

To increase the strength the web is increased gradually in thickness from the point toward the shank by drawing the cutters apart. This decreases chip room and to avoid this defect the spiral is increased in pitch and the flute widened to make up the chip room.

The shape of the groove affects the power and the shape of the chip and experiments by the Cleveland Twist-Drill Company are interesting. The groove in Fig. 1 does not give a good cutting edge, especially near the center, as it does not allow a full curl to the chip. Fig. 2 is a very free cutting-groove, the chips curl up to the full size of the groove and this reduces the power required to bend the chips. Fig. 3 is an even better form as it rolls a chip with each turn conical so that one lays inside the other and makes a much shorter chip from the same depth of hole.

The angle of spirals varies from 18 to 35 degrees according to the ideas of the maker. In theory the finer the pitch or the greater the angle, the easier it should be to cut and curl the chip. But this gives a weak cutting edge and reduces the ability to carry off the heat, and it does not clear itself of chips so well. After a long series of tests the same firm adopted 27 degrees for the spiral. This angle makes the spiral groove of all drills start at the point with a pitch equal to six diameters of the blank, the increase in twist being a constant function of the angular movement of rotation of the drill blank. This angle is based on holes from one to three diameters deep. For deeper holes a smaller angle might be advisable and greater angle for holes of less depth. There is practically no difference in torsional stress with the angle between 25 and 30 degrees.

SHARPENING DRILLS

Drills should be sharpened so as to cut the right size and with as little power as possible. To cut the right size both lips must be the same length and the same angle. A gage as shown in Fig. 4 will help both to get the angle and to grind them central. This gives the usual lip edge of 59 degrees. Fig. 5 shows how you can see if both lips are ground alike, but does not give the angle. Fig. 6 is a suggestion by Professor Sweet of relieving the drill back of the cutting edge, making it similar to a flat drill in this respect.

For drilling brass or for any thin stock where the drill goes clear through, it is best to grind the cutting edge parallel with the axis of

the drill. This does away with the tendency to draw into the work. Fig. 7 shows how this is done.

It is sometimes necessary to thin the point of the drill to get best results. This requires care in grinding but can be done as shown in Fig. 8.

The best all-around clearance angle is 12 degrees, though for softer metals 15 degrees can be used. The 12 degrees is the angle at the cutting edge, but this should increase back of the cutting edge so that the line across the web should be 45 degrees, with the cutting edges. This is important, as it not only saves power but prevents splitting in hard service. The point of the drill should look like Fig. 7 or Fig. 8. Fig. 9 shows the clearance angle and the right angles for the drill point.