A Vernier Caliper is a type of visual measurement instrument that allows users to precisely, in engineering terms, measure a product. First invented in 1631 by Pierre Vernier, caliper design has since changed and accuracy has improved. Today digital calipers allow for greater accuracy and ease of use. Some even have computer connectivity. Two sets of jaws allow internal and external dimensions to be measured (for example inner and outer diameters of tubing). The vernier scale is used to indicate small deviations in a linear fashion between two jaws or a sliding arm. Vernier Calipers are used widely across engineering industries from machinists performing quality control tasks to research engineers conducting experiments.
Measuring the thread diameter of an M4 bolt using EFP digital vernier calipers
We believe that these are one of the most fundamental tools for an engineer and no matter what sector of engineering, there will always be a point in time in which you will be required to precisely measure a component. Another reason for the importance of owning vernier calipers is that as you will see in this blog, they are very easy to use and can perform a variety of measurements.
For this reason we stock stainless steel and carbon fiber composite digital vernier calipers with 0.1mm resolution for internal, external, step and depth measurement. With a range of 150mm the calipers are suitable for both DIY and professional use. You can choose between metric and imperial units.
Before we understand how to use vernier calipers we must first understand the basic components that make up a vernier caliper. Below are the 2 verniers we currently (as of April 2018) stock with the components labelled alongside them.
EFP Stainless Steel Digital Vernier Calipers
EFP Plastic Digital Vernier Calipers
Now that you are aware of the basic components we will run through step-by-step from basics (sorry if you already understand the basics!) on how to use them.
Prior to any calibration or new work / once you have completed your work, you should always clean your vernier calipers. This prevents any debret getting between the jaws or grease affecting its sliding scale. In order to calibrate the vernier calipers, the lock screw must first be loosened (if you are using the stainless steel version). From there close the jaws and select the zero button. To check if they have calibrated you can either open or close the jaws and ensure that it is still set to 0 or you can check by measuring a pre-calibrated length. This may be in the form of a steel machined block with the Theoretically Exact Dimension (TED).
Place the object in between the two jaws so that they touch opposite ends of the object making sure the object is held firmly but don’t press too tight. If you need to measure an internal diameter, then insert the upper jaws in to the cavity and open them till they touch the sides. Tighten the locking screw to hold the jaws in position if the vernier calipers have a locking screw. We currently only provide digital calipers but if you were to read from a vernier scale read the division just before where the zero mark of the vernier scale is aligned. So if the zero mark aligns just after the fifth division between 3 and 4 the main scale reading is then 3.5mm. If it were to be just after the 7 and 8 mark it would be 3.7mm.
Following this you need the find the minor deviation. To do this find the mark on the vernier scale which lines up perfectly with a mark on the main scale. The vernier reading can then be found by multiplying the least value of the vernier scale with the number of divisions until that mark. For example if the least value is 0.01 mm and the 7th mark of the vernier scale is lined up perfectly then the vernier scale reading is 7 x 0.01 = 0.07mm. Following this the major and the minor deviations need to be added together. For this example the major deviation would be 3.5mm and the minor would 0.07mm giving a total value for the measurement of 3.57mm. Of course, this is only required if digital calipers are not available. If calibrated and stored correctly, digital calipers provide a much faster reading than manually read calipers.
For internal and depth measurements, if you are reading from the same vernier scale, you will need to follow the guidelines as stated above. However, with digital calipers, to find the internal measurement you simply have to extend the upper jaws to the desired location and measure using the flat surface of the upper jaw. This is particularly useful for measuring internal geometry such as holes and slots. Ensure that you have firmly grasped the extremities but do not apply too much force. At this point you can either read the value or if a lock screw is available, tighten at the measurement point and remove the calipers to view the measurement.
Depth measurements are probably the most complex measurement that you will perform with a vernier caliper. The reason for this is it relies on the user ensuring that the depth rod is parallel to the extremity measurement surface. To perform this measurement, open the calipers with the thumb screw or push depending on which type you have and do this until the depth rod has reached its desired measurement location whilst using the end of the main scaled frame as a stop. From this point the measurement can either be taken or the user can lock that measurement and remove to read the value.
Thanks for taking the time to read this and hopefully it will be useful in undertaking your job or studies in engineering. If you do not have a set of vernier calipers or are needing a new high quality pair, please check out our store following the link below: