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MEASURING FINE PITCH SCREW-THREAD

DIAMETERS

THE accompanying table should be of service to those using the three-wire system of measurement as the constants cover the finer pitches and may be easily applied to screw threads of any diameter. The diagrams, Fig. 14, make the method of application so plain that no description appears necessary.

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CONSTANTS FOR USE WITH THE 3-WIRE SYSTEM OF MEASURING

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MEASURING ACME 29-DEGREE THREADS

THE diameter of a wire which will be flush with tops of thread on tap when laid in the Acme thread groove, Fig. 15, will be found as follows:

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Wires of the diameter given in the table come flush with the tops of tap threads and project .oro above the top of screw threads.

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TABLE OF WIRE Sizes for Measuring Acme STANDARD 29° SCREW

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TABLE OF BROWN & SHARPE 29° WORM THREAD PARTS

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.6866.3350.3100.5000 .3183 .05

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.8 .5492 .2680.2480.4000 .2546 .04 •532 •552 .6666 .4577 .2233 .2066 .3333 .2122

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3433 .1675 .1550 .2500 .1592
.2746.1340.1240 .2000 .1273

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03334433 | 4599 .0250 3325 345 .0200 .2660 .276 3333 .2289.1117.1033 .1666.1061 .0166 .2216.2299 .2857.1962.0957.0886.1429 .0909 .250 .1716 .0838 .0775.1250 .0796 .0125 .1637 .1725 .2222.1526.0744.0689 .IIII .0707 0111.1478 .1533 .2 .1373 0670.0620.1000 0637 .0100 .1330.138 .1666 .1144 .0558 .0517.0833 .0531 .0083.1108 .115 .1428 0981.0479 0443.0714.0455 .0071 .095 .0985 .125 .0858 .0419.0388.0625.0398 .0062.0818 .0862 .IIII .0763 0372 0344 0555.0354.0055 0739 .0766 .IO .06870335.0310.0500 .0318.005 .0665 .069 .0833 0572 .0279 .0258.0416 .0265.0042.0551.0575 .0625 .0429 .0209.0194 .0312.0199.0031 .0409.0431 20 .050 .0343 0167 .0155 .0250 .0159 .0025 0332 0345

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MEASURING BROWN & SHARPE 29-DEGREE
WORM THREADS

THE diameter of wire for Brown & Sharpe worm thread, Fig. 16, for each pitch, that will rest in the thread groove on the thread angle and be flush with the tops of the finished threads, is found as follows; Rad. of wire section (see table) side opp. side adj. X tan.

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FIG. 16. Measuring Brown & Sharpe Worm Threads.

TABLE OF WIRE SIZES FOR MEASURING B. & S. 29° WORM THREADS

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WORM WHEEL HOBS

HOBS are made larger in diameter than the worm they are used with by the amount of two clearances. The Brown & Sharpe method is to make the clearance one-tenth of the thickness of the tooth on the pitch line or .05 inch for a worm of one pitch. If the worm was 3 inches outside diameter, which would be a fair proportion for this pitch, the outside diameter of the hob would be 3+ (2 X .05) = 3.1 inches. The thread tool would be .31 inch wide at the point and would cut .6360 + .1 = = .7366 deep, leaving the top of the thread the same thickness as the bottom, which is different from the worm. The land L should be made as near the proportions given as possible.

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The diagram Fig. 17 shows the shape and proportions of the thread of a worm hob, and Fig. 18 shows the proportions for the depth of tooth, the lead and the outside diameter. In these diagrams:

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