Use, accuracy and How to read The Micrometer Use, accuracy and How to read

Use and accuracy A micrometer is a precision instrument which is used to measure components to a very high degree of accuracy They can be purchased in metric or imperial ranges Measuring range is 25mm metric (0-25, 25-50 etc) 1” imperial (0-1”, 1”-2” etc) Accuracy is one hundredth of a millimetre for the metric version (0.01mm) or one thousandth of and inch for the imperial version (0.001”) To get an idea of the accuracy, a single hair taken from your head would measure around 4 hundredths of a millimetre (0.04mm).

The main parts

How to use The thimble is rotated in an anticlockwise direction until the gap between the anvil and the spindle is slightly larger than the item to be measured. The item to be measured is then held between the anvil and the spindle The thimble is then rotated clockwise using the ratchet until the anvil and spindle come into contact with the item (at this point the ratchet will begin to click this indicates the correct tension has been achieved). The spindle is then locked and the item is removed so that the reading can be taken.

The scales As the thimble is rotated anticlockwise two scales become visible on the barrel, the top scale is whole millimetres (each increment/division is 1mm) the bottom scale is half millimetres increments (0.50mm). There is a line dividing these two scales this is called the datum line. There is a third scale on the circumference of the thimble which is divided into 50 increments each one representing one hundredth of a millimetre (0.01mm)

How to read Firstly look at the top scale and note the number of whole millimetres revealed (6.00mm) Secondly look at the bottom scale and note if the corresponding half millimetre increment has been revealed (0.50mm) Finally look at the scale on the thimble and note the reading which coincides with the datum line (0.26mm) When you have obtained these three readings you need to add them all together to give the measurement. (7.00+0.50+0.26= 7.76) therefore the diameter of the component 7.76mm.

Try these examples Example 1 Example 2 Example 1= Example 2 =

Using a micrometer measure the diameter of the piece of bar and record the size on the drawing

Using a micrometer measure the 5 diameters on the stepped shaft and record the sizes on the drawing