Micrometer Gauge: Pratt, 1878

A micrometer clamps the work between a fixed abutment and the tip of a fine screw. Both faces must be smooth and very hard, but tempering a finished screw changes it: the heat expands the metal, part of the expansion stays, and the cooling is uneven, so a screw that was accurate before hardening often is not after. George M. Pratt of Middletown, Connecticut, patented the remedy in 1878, US 202,866: leave the screw untempered and give it a socket at its end for a separate tip of steel tempered as hard as possible. A worn tip is simply replaced. He also shaped the horseshoe frame widest at the middle and tapering towards the ends, so it is stiff where it most needs to resist springing but lighter overall.

高级

Workshop process

说明

Frame

Make the horseshoe frame widest at the middle of the bow and tapering towards both ends, where the abutment and the screw bearings sit.

此步骤所需材料：

千分尺马蹄形尺架1 个

Screw

Cut the micrometer screw in steel and leave it untempered. Form a socket in its measuring end.

此步骤所需材料：

千分尺测微螺杆1 个

所需工具：

金属车床

Tip

Make the tip separately, with a shank that fits the socket closely, and temper it as hard as possible.

此步骤所需材料：

淬硬千分尺测头1 个

所需工具：

热处理炉

Assemble

Insert the tip's shank into the screw's socket. Fit the adjusting abutment screw in the other end of the frame; the work is measured between its flat face and the tip.

此步骤所需材料：