Features of Depth-micrometer

 DEPTH MICROMETERS

. name the parts of a depth micrometers

. the constructional features of a depth micrometer


Constructional features

The depth micrometers consists of a stock on which a graduated sleeves is fitted.

The other end of the sleeve is treaded with a 0.5mm pitch 'V' thread.

A thimble which is internally threaded to the same pitch and form, mates with the threaded sleeve and slides over it.

The other end of the thimble had an external step machined and threaded to accommodate a thimble cap.

A set of extension rods is generally supplied. On each of them the range of sizes that can be measured with that rod, is engraved as 0-25,25-50,50-75,75-100,100-125 and 125-150.

The extension rods can be inserted inside the thimble and the sleeve.

The extension rods have a  collar-head which helps the rod to be held firmly.

The measuring faces of the stock and the rods are hardened, tempered and ground. The measuring face of the stock is perfectly machined flat.

The extension rods may be removed and replaced according to the size of depth to be measured.

Graduation and least count

On the sleeve  a datum line is marked for a length of 25mm. This is divided into 25equal parts and graduated, each line representing one millimeter, each fifth line is drawn a littile longer and numbered. Each line representing 1mm is further subdivided into two equal parts. Hence each subdivision represnets 0.5mm.


The graduations are numbered in the reverse direction, to that marked on an outside micrometer.

The zero graduation of the sleeve is on the top and the 25mm graduation near the stock.

The bevel edge of the thimble is also graduated. The circumference is equally divided into 50 equal parts and every 5th division line  is drawn a littile longer and numbered. The numbering is in the reverse direction and increases from 0,5,10,15,25,30,,35,40,45 and 50(0).


The advancement of the extension rod for one division movement of the thimble will be equal  to 0.5/50=0.01mm

This will be the smallest measurement that can be taken with this instrument, and so, this is the accuracy of this instrument.

Uses of depth micrometer

Depth micrometers are special micrometers used to measure

The depth of holes

The depth of grooves and recesses

The height of shoulders or projections.


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