How to use calipers?

Although it’s not that difficult learning how to use calipers you may find that after reading through this article there are things that you can do with a caliper that you were unaware of.

Why use calipers instead of a ruler?

The reason as to why you would use calipers instead of a ruler is accuracy and ease of use.

A even a basic digital caliper will display a measurement to a tenth of a millimeter. Try to measure that with a ruler, or even a ruler and a magnifying glass.

How does a caliper work?

While a micrometer looks a bit like a clamp, a caliper looks a bit like an adjustable spanner. Calipers used to be made of steel. A lot of the newer, cheaper digital ones are made of carbon fiber. A caliper has jaws to measure an object and a sliding body.

This is linked to a digital display.

Try to keep your caliper in a box when it’s not in use so not to get it damaged. Remember a caliper is a precision instrument. If you damage the jaws you cant expect it to measure properly.

Measuring things with a caliper

A caliper can measure many things. It can be a real eye opener if you’ve only ever relied on a steel ruler. I built a CNC machine for home and hobby use. I was amazed at how accurately it could work on materials. But this new ability to be able to make things to a .1 millimeter accuracy brought new problems. If I couldn’t actually measure to that resolution how could I do the basics like calibrate the CNC machine in the first place?

The answer is you can’t. I tried to use a steel ruler and a magnifying glass to accurately measure. It was clear I needed something better. Step up “the caliper”.

If you are unfamiliar with what a CNC machine is, so was I a couple of years ago. Basically mine is a router that can be moved around left and right, backwards and forwards and up and down. Its moved by linear guides and stepper motors to .1 of a mm by a computer.

Using software you can get it to cut out complex shapes. You can make complex interlocking project boxes out of acrylic sheet. Cut out complex panels and even make PCB’s out of fiberglass sheets. If you want to know more about what CNC machines can do read my article here.

I tried to make a front panel for a project that aligned to components mounted on a PCB. There were square holes for push button switches so if my machine wasn’t calibrated correctly it wouldn’t fit.

CNC machine calibration

The method I used to calibrate the CNC machine was to do a simple design on the laptop of a 10cm by 10cm square. Then get the machine to cut it out of scrap acrylic. Then measure the actual size of the square. Depending on the actual size there was a formula to work out figures to input. This was input and stored in the machine. Then running the same program again and the square should measure exactly 10 cm by 10 cm.

Using the caliper

When you first turn on your caliper, slide the jaws open and wipe with a soft cloth to make sure there is nothing on them to get in the way of the measurement. Obviously don’t be too vigorous and don’t use anything abrasive. This is a precision measuring tool!

Slide the jaws closed and check that the display reads zero. If it doesn’t press the zero button. With the caliper reading zero, slide the jaws open and place the item you want to measure between them and slide them shut. The display will now tell you the measurement. You can use the button to select between metric and imperial. I only use the metric setting but its good to know I have the option of imperial if I need it.

Using the caliper I can check that the actual object has been cut out to the design size . I can also check both edges to confirm that the part is square.

Internal caliper measurements

One of the advantages a caliper has over that of a micrometer is that most calipers can measure internal dimensions as well as external ones.

You do this by using the inside jaws at the top of the caliper. With this function you can accurately measure square panel cut outs for things. You can also use this the measure the internal diameter of round holes.

Thing to bear in mind when measuring

When you are measuring things make sure that they are square in the jaws. If they aren’t then you wont get an accurate reading. This goes for internal measurements and depth measurements. Keep it square!

Caliper depth measurements

I didn’t even realise my digital caliper could do this. Although I had noticed the bit of rod type thing that came out of the bottom when you slid the jaws open, I wasn’t aware of what it actually did. I now know you can use this to measure the depth of things like holes for instance. It’s not something that I do but its nice to known that I can if I need to.

Caliper step measurement

Another function I didn’t realise that my caliper could do is the step measurement. Push the gauge against an object and slide it to the step. Then you have an accurate measure of the step size.