What Are They and Why You Should Use Them?
Originally Posted at 15:59 - 18th October 2021 - EMG Precision
Introduction: What are Vernier Calipers?
Vernier calipers are among a variation of 3 products that serve the same purpose. Vernier Calipers, Dial Calipers and Digital Calipers all take a reading of a distance measured with a high level of accuracy and precision. The only real difference is the method in which the reading is taken. With Dial Calipers the operator must read measurements from several indicators on a dial. A digital caliper displays the distance somewhat instantly on some sort of screen, typically LCD, (Liquid Crystal Display). A vernier caliper must have multiple measurements taken from different scales, and a calculation made to get the final result.
Calipers are extremely common in machine shops. In fact, It would probably be safe to say that every machine shop in the world has some sort of variation of the caliper. They are extremely useful for general dimension measurements as well as measuring the diameter of round objects or holes. A good example of the versatility of a caliper would be to imagine a hollow cylinder boss. A vernier caliper could be used to measure the outside diameter of the tub, the inside diameter of the hole and the depth of the boss.
How Accurate are Vernier Calipers?
It is generally considered that vernier calipers, or calipers of any type, are less accurate that micrometers of the same league. It is typical for a pair of high quality vernier calipers to be correct to 10 microns, or micrometers (0.01 mm / 1/1000th inch.). A high quality micrometer on the other hand most often measures accurately and faithful to its name, down to single micrometers, or microns (0.001 mm). Vernier calipers use a simple linear input, to linear output while micrometers use rotary input to convert into rotary linear movement of the spindle. This enables micrometers to be generally more accurate. It also has the effect of making calipers easier to use. Micrometers can apply a large amount of force which if overtightened, can cause skewing of the measurement to smaller values that reality. The repeatability consistency of micrometer readings takes more experience and practice to become competent. Ver Calipers, or other types of caliper do not require this level of subtle skill to use.
What are the Pros and Cons of Using Vernier Calipers?
Vernier Calipers are literal a staple and frequent diet of the mechanical engineer. Like a multi meter is to an electrician, a set of vernier calipers are to a CNC machinist. Here we will take a look at the Pro's and Con's of using Vernier Calipers...
What are the Pros of Vernier Calipers?
The headline features and benefits of Vernier Calipers are as follows...
- Rugged & Long-Lasting Accuracy.
- Coolant Proof.
- Magnetic Field Proof.
- Largely Shockproof.
- Typically cheaper than digital alternatives.
- No batteries required.
- Longer lengths can be measured over micrometers.
What are the Cons of using Vernier Calipers?
The limitations and considerations of using vernier calipers are as follows...
- Harder to read than Digital Calipers.
- Basic calculations have to be done so they are usually slower to use.
- Relatively easy to mis-read the last digits.
- User fatigue can be a factor on your error-rate.
- Not as accurate as micrometers in general.
How do Vernier Calipers Work? GIF Video Animation?
How the vernier calipers are open and closed and how the reading is taken.
Below is a GIF animation of the principal on how Vernier Calipers are to be used. We cover this in more detail in another article (link below) but here is a brief introduction to give you an idea of how it works courtesy of Joaquim Alves Gaspar.
Thank you to the Author: Joaquim Alves Gaspar for the above GIF.
What are the parts of a Vernier Caliper?
1) Outside Large Jaws.
Typically used to measure the outside, or external diameter of an object, like a cylinder or rod. Also used for measuring the width of features like thickness or a boss width.
2) Inside Small Jaws.
Intended to measure the internal diameter or distance of an object like a hollow cylinder or a pocket feature width.
3) Depth Probe, or Depth Rod.
Used to measure the depth of objects like a hole of or cavity pocket feature.
4) Main Scale (In Metric Graduations).
Scale marked metric graduations, usually in millimetres to help measure length correct to 1mm.
5) Main Scale (Imperial Graduations).
Scale marked imperial graduations, usually in inches and fractions to help measure length in imperial.
6) Vernier Scale (Metric Graduations).
Used to measure interpolated measurements accurate to 0.1 mm or better.
7) Vernier Scale (Imperial Graduations).
Used to measure interpolated measurements accurate in fractions of an inch.
8) Lock Screw or Retainer.
Used to lock measurement positions to make it easier to read results without worrying about false adjustment.
What is Zero-Point Error Compensation on a Vernier Caliper?
Vernier Calipers are strong and durable, but in the event of a powerful impact or drop, the calibration may become off-zero. Whereas a digital caliper may become completely useless after a bad drop, manual calipers may no longer return to exact zero when fully closed. All is not lost though. You can fully close the jaws and take the reading to establish how far away from zero the calipers are. This distance read off the scales can then be added or subtracted from the final measurement to give you an accurate reading.
How to Interpret a Vernier Calipers Specified Resolution & Accuracy?
A set of vernier calipers should state at least two sets of accuracy specifications to let the operator know how accurate, or to what tolerance the calipers are designed to measure to. We will define what both these measurements mean below...
What is the Resolution on Vernier Calipers?
A quality pair of Vernier Calipers should state 2 measurements of accuracy. One of these is Resolution. This is basically the smallest graduation of markings on the smallest scale. In other words, it is the smallest distance that you can read from using the scales used on that model. In most cases, on a high quality pair of calipers, this is 0.01 mm.
What is the accuracy specification of Vernier Calipers?
The second quoted specification for how precise a set of calipers are is the 'Accuracy'. This is the overall accuracy of the instrument over any measurement. For example, if a part is measured at 102.04 mm that part would be accurate to plus or minus whatever the accuracy specification is.
Thank you for reading our article on Vernier Calipers. We hope you enjoyed it and found it useful. I for one use a pair of vernier calipers all the time. I even have a kitchen pair in that junk jaw that everyone has, that i use for whatever it is i might need. They are extremely useful for a range of measurement needs and my Daughter thinks they are good to open packages with too.
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