Knight's Mechanical Encyclopedia, S., Screw-tap.

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19th-Century American

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Screw-tap.

An instrument for cutting the interior thread on a hollow screw. For cutting the corresponding thread on the screw rod or bolt, a screw plate or dies are employed.

Screw taps and dies.

These are held in a die-stock, an improved form of which is shown at a. This is adapted to receive dies having differentsized threads, which are held by a screw; the sides of the opening being plain at one end for the ready introduction of the dies, and having ribs at the other, which fit grooves in the dies and prevent their falling out when fixed. c d illustrate the action of the common two-part die on the rod placed centrally between its parts. In the first the die has the same curvature as the finished screw; in the latter that of the uncut rod. In either case but a part of the cutting surface acts, and the tendency is to cut an imperfect thread.

This is partially remedied by cutting the dies of a curvature intermediate between the two.

To obviate this defect as far as possible, Sir J. Whitworth introduced the arrangement shown at e.

The two narrow dies act as cutters, and are advanced toward the center of the rod on which the thread is being cut by turning the thumb-nut o, which advances the slide-place p: the broader die opposite serves principally as a guide for the thread.

f are tools for chasing exterior threads, and g for interior threads on work held in a lathe.

h is a section, and i k elevations of taps; these have a square shank fitting in an appropriate holder like the die-stock, or sometimes the die-stock itself is adapted for this purpose.

b is the screw plate; this is principally used for small work, and has a series of screw-threaded apertures of various sizes adapted for different-sized wire.

Screw-thread gage (one-half size, linear).

1877.

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Knight's Mechanical Encyclopedia
Knight, Ed.

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Screw-tap.

Knight's Mechanical Encyclopedia Knight, Ed.

This text is part of:

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Table of Contents:

Screw-tap.

Knight's Mechanical Encyclopedia
Knight, Ed.