What is a Vernier Caliper?
A vernier caliper is a device that is used to measure linear dimensions. It is also used for the measurement of diameters of circular objects with the aid of the measuring jaws. In machine shops, the term “caliper” is often used when compared to a “micrometer”. There are various types of calipers, but all are designed in the same way.Â
What are the parts of the Caliper?
As seen in the image below, a caliper has upper and lower jaws, main scale, lock screw, thumb screw, depth rod and a vernier scale.
What should one be aware of while using a Vernier Caliper?
A variety of factors can cause errors when measuring with a caliper:Â
- Parallax effects
- Excessive measuring force because a caliper won’t conform to Abbe’s principle
- Differential thermal expansion due to a temperature difference between the caliper and workpiece
- The effect of the thickness of the knife-edge jaws, and the clearance between these jaws during measurement of the diameter of a small hole
Although there are also other error factors, these factors are included within the instrumental error tolerances.Â
What is ‘parallax error’?Â
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, for example, our eyes have different lines of sight while viewing the same object. The process by which the brain exploits the parallax is due to the displacement caused in the apparent position of the object due to the viewing angle, i.e., other than the angle that is perpendicular to the object.Â
Tips on how to effectively use the Vernier Caliper?
- When reading the scale, look straight at the vernier graduation line when checking the alignment of vernier graduation lines to the main scale graduation lines.
- Always use constant Force while using the caliper. Too much of force can damage the part that needs to be measured, and too little force gets insufficient contact with the part and gives a wrong measurement.
- While taking measurements, make sure that measurements are not taken on the edge of the jaws. Instead, take a measurement on the machined area and preferably on the top which will give better consistency, accuracy, and repeatability.
- Clean the contact points or the jaws using a lint-free cloth before measuring
- When you close the jaws, ensure that no light passes through the jaws, if light passes through, there may be a parallelism error that has to be repaired
- Avoid damaging the scale of a digital caliper and do not engrave anything on it with an electric marker pen
- Avoid damaging a caliper by subjecting it to impact with hard objects
- If the caliper is not going to be used for a longer period, remove the battery, and do not leave the jaws of the caliper completely closed during storage
Bombay Tools Supplying Agency Pvt. Ltd has an extensive range of vernier calipers and can advise the best product for your requirements. You can reach them on info@btsa.in for more information.
To know the exact way in which a vernier caliper should be used, you should see the following video:
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