Immagini

DESCRIPTION

Exhibit 896 is a micrometer, also called Palmer from the name of its widely known maker, an instrument for measuring small thicknesses (from 0 to 25 mm) with great precision (1/100 mm).

The micrometer Palmer consists of a screw V (see design:1) with a pitch of 0,5 mm, fixed to a drum H on which is inscribed a circular scale divided in 50 parts. The screw is housed in a nut on which is inscribed a longitudinal scale in mm with divisions of 0,5 mm. With each turn the screw advances or backs up 0,5 mm while a rotation of the screw by one division inscribed on the drum corresponds to 1/00 mm.

The nut is mounted on a semicircular arc whose end point stop A is in contact with the precision screw when the instrument signals zero on both scales.

The friction knob F permits reproducibility of measurements by applying the same force on the specimen to be measured as well as the setting of the truest zero.

The measurement is done reading the mm on the longitudinal scale on the precision nut and the hundredths on the round scale on the drum. Before making a measurement, one controls that the reading is zero when the screw is up against the end point stop A.

The instrument is conserved in its case along with a metal disk for calibration.

BIBLIOGRAPHY

• [1] Eligio Perucca,"Fisica Generale e Sperimentale", Vol I UTET,Torino, 1937-xv.P.35.

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