REAMER CLEARANCE

Ground with Cup Wheel 3" dia.-Tooth Rest to be Set Central with Emery Wheel Spindle. Set Work holding Centers above Emery Wheel Center by Amount given below in Tables No. 1-2 and 3

TABLE I

Hand Reamer for Steel Cut'g Clearance Land .006 Wide

TABLE 2

Hand Reamer
for Cast Iron
and Bronze
Cut'g Clear-
ance Land
.025 Wide

TABLE 3
Chucking
Reamer for
Cast Iron and
Bronze Cut'g
Clearance
Land .025

Wide

For setting tooth rest to obtain Giving distance B for setting 5° or 7° clearance when grinding work centers and tooth rest beperipheral teeth of milling cutters low center of wheel spindle to with cup-shaped wheel. Tooth obtain 50 or 7° clearance with rest is set below work centers as wheels of different diameters at A, the distance being found in when grinding with periphery of the table below. disk wheel.

SCREW MACHINE TOOLS, SPEEDS

AND FEEDS

BOX TOOLS AND CUTTERS

The

THE general principles of two types of box tools using respectively tangent and radial cutters are represented in Figs. 1 and 2. former type is generally used for roughing and the latter for finishing. The tangent cutter in the type of box tool shown in Fig. 1 lies in a slot formed parallel to the bottom of the box but at an angle, usually

ten degrees, with the front of the box, thus giving the desired rake at the cutting point. Finishing cutters of the type in Fig. 2 are straight on the end, located square with the work and ordinarily ground as indicated to give 7 to 10 degrees front clearance for steel and 5 to 8 degrees for brass.

The tangent cutter is sharpened by grinding on the end, and compensation for the grinding away of the metal is made by adjusting the cutter forward, whereas in the radial type of cutter in Fig. 2, frequent sharpening cannot be done without resulting in lowering the cutting edge of the tool below the center of the work, unless a substantial part of the tool be sacrificed. The radial tool, however, is easily ground accurately on face a, which is the edge governing the finish; while the corresponding face on the tangent tool is rather difficult to grind so as to produce as smooth work.

The sizes of steel recommended for box-tool cutters are as follows: For box tools used for stock diameters up to inch, inch square; up to inch diameter, inch square; up to inch diameter, 1 inch square; up to inch diameter, inch square; up to 1 inch diameter, inch square; up to 1 inches diameter, inch square.

HOLLOW MILLS

THE teeth of hollow mills should be radial or ahead of the center. With the cutting edge ahead of the center, as in Fig. 3, the chips as produced are caused to move outward away from the work and prevented from disfiguring it. With the cutting edge below the center, rough turning will result. With the cutting edge greatly above the center, chattering occurs About one tenth of the cutting diameter is a good average amount to cut the teeth ahead of the center.

When the chips produced from any turning or boring cut curl nicely, it is indicative of a free cutting action; but these chips are very troublesome on the automatic screw machine. In making hollow mills for the automatic, part or all of the rake to the cutting edge is generally sacrificed.

The table under the hollow mill in Fig. 3 gives proportions of mills from to diameter, showing the amount to cut the teeth ahead of the center, the taper of the hole, etc.

Finishing.. 18 32 1 32 18 32 32 fo

Roughing. 072.104.135-16-197-229-26

.291.322.385.510 635.760

It is good practice in making spring screw dies to either hob out the thread with a hob tap 0.005 to 0.015 inch over-size, according to size, and in use to spring the prongs to proper cutting size by a clamping ring, or to tap the die out from the rear with a hob tap tapering from inch to inch per foot, leaving the front end about 0.002 inch over cutting size, and in this case also to use a clamping ring. Both of these schemes are for the purpose of obtaining back clearance and are effective. Of the two the use of the taper hob is to be preferred.