What is a caliper (vernier caliper)?
A caliper (Dutch: schuifmaat) is a measuring tool made of metal or plastic for accurately measuring small distances. It consists of a fixed beam with a millimetre scale and a sliding part. Both parts have a jaw: between the large jaws you measure outside dimensions, between the small “ears” at the top you measure inside dimensions, and with the rod that slides out at the end you measure depths, such as the depth of a drilled hole or a rebate.
Types of caliper:
- Analogue with vernier: the sliding part carries an auxiliary scale, the vernier. Depending on the model, it lets you read to 0.1, 0.05 or 0.02 mm.
- Dial caliper: the fraction of a millimetre is read on a small dial. Easier to read than a vernier.
- Digital: the measurement appears on a display, often with a resolution of 0.01 mm, switching between mm and inches and a zero button to measure from any point.
Reading a vernier: first read the whole millimetres on the fixed scale, to the left of the zero of the vernier. Then find the line on the vernier that lines up exactly with a line on the fixed scale. That line gives the fraction. If the zero is just past 23 mm and the 0.85 line coincides, the measurement is 23.85 mm.
Application
In construction and the workshop, a caliper is used for, among other things:
- determining the diameter of bolts, screws, wall plugs and drill bits;
- measuring the thickness of sheet material, glass, profiles and tubes;
- checking the inside diameter of pipes and the depth of holes and rebates;
- setting up machines and checking timber joints.
Tips:
- Check the zero point: close the jaws and see whether the caliper reads zero. On a digital caliper, press zero with the jaws closed.
- Measure square and without squeezing: keep the jaws square to the workpiece and press lightly. Squeezing too hard gives a reading that is too small.
- Measure with the base of the jaws, close to the beam; at the tips the measurement is less accurate.
- Keep it clean and dry: sawdust and dirt under the slide cause measuring errors. Remove the battery from a digital caliper that will not be used for a long time.
- For even more accurate work, use a micrometer.
Related Terms
- Vernier scale
- Micrometer
- Folding rule
- Tongue and groove
- Steel sections
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