Calipers/Verniers – Types -  For Woodworking

Let me introduce you to another group of shop measuring tools commonly used in woodworking.

The Vernier Caliper, The Dial Caliper – specifically a Fractional Dial Caliper and a Digital Vernier Caliper.

Calipers allow you to take four (4) kinds of measurements:

Outside

Inside

Depth and

Step

Whether they are vernier, dial or digital, they all have 2 key components – a main body and a slider.

The main body usually has 2 major scales marked on it and

The slider also has 1 or 2 minor scales marked on it.

Let us look at each one separately.

Basic Plastic Vernier Caliper

This vernier caliper has 2 major scales on the body.

The upper scale is in inches and the smallest increment displayed of 1/16 of an inch.

The common increments of 1/8, 1/4 and inches are displayed with larger markers.

The lower scale is in millimeters (mm) with the smallest increment displayed being 1mm.

Again common increments for 5mm and 1cm (10 mm) are displayed with larger markers.

The top of the slider has what is known as a minor scale allowing you to take measurements up to 1/128 of an inch.

And the lower scale on the slider is also known as a minor scale allowing you to take measurements up to 0.05 of a mm.

Basic Metal Imperial Caliper

This vernier caliper is for imperial measurements only.

The body has 2 major scales, the top scale is in 16ths of an inch and the lower scale is in 32nds of an inch.

The slider on this model only has 1 minor scale on the top side of the open window area, allowing you to subdivide the 1/16 increments up to 1/128 of an inch.

Simple Fractional Dial Caliper

The body of this caliper has 2 major scales, the upper is in millimeters (mm) and the lower is in inches.

But the lower scale is not subdivided in fractional increments but in decimal increments, meaning each inch is divided into 10.

I refer to this as simple fractional dial caliper because the inner dial indicator shows the most common full fractions in 1/8 multiples such as 1/8, 1/4, 1/2, 5/8, 3/4, and 7/8.

The inner dial markers also show increments of 1/64 of an inch which allows you to take measurements of 1/32 of an inch and 1/16 of an inch.

The outer dial markers (in the yellow area) are in 0.01 of an inch.

So looking at the dial, we see that the measurement shown representing either an outside, inside, depth or step fractional measurement is 1/4 of an inch.

Using the body upper major scale we can see that is it 6mm.

Its decimal equivalent is over 2/10ths of an inch from reading the lower main scale + 0.25 of an inch reading the dial in the yellow area which totals 0.250 of an inch in decimal equivalents.

See how easy it is.

Advanced Fractional Dial Caliper

I refer to this caliper as the advanced fractional dial caliper because the inner dial indicator shows the most common full fractions in 1/16 multiples, such as 1/16, 1/8, 3/16, 1/4, 5/16 up to  15/16ths.

I refer to this caliper as the advanced fractional dial caliper because the inner dial indicator shows the most common full fractions in 1/16 multiples, such as 1/16, 1/8, 3/16, 1/4, 5/16 up to  15/16ths.

The main body has 2 major scales, upper scale is in millimeters (mm), and the lower major scale is in inches with 1/16 increment markers.

Fractional measurements are read on the outside ring of the dial in the white area.

Each increment in the white area of the dial is in 1/64ths of an inch.

Here we are reading 1/4 of an inch. This can also be read off the lower major scale of the body.

Again, using the upper major scale of the body we can read 6mm also, the metric equivalent of 1/4 of an inch.

The inner dial markers( in the green area) are in 0.01 of an inch increments and labels the markers for 0.100, 0.200 etc.

So what we are seeing is 0.200 + 5 spaces of 0.01 each giving us a measurement of 0.250 of an inch.

The decimal equivalent of 1/4 of an inch.

Simple right?

Fractional – Decimal – Metric - Digital Caliper

Fractional because the display can be changed to display fractions.

Decimal because the display can be changed to display decimals.

Metric because the display can be changed to read in millimeters.

The body of this caliper also has 2 major scales, the upper scale is in millimeters and the lower scale is in inches.  Once again, the lower scale is subdivided into 10 sections giving us the decimal reading.

The smallest fractional measurement this caliper is capable of is 1/64th of an inch.

Here we are reading a fractional measurement of 31/64.

That is 1/64ths of an inch smaller than 1/2 of an inch.

If the reading was 32/64 and we divide that by 2 equals 16/32, and divide that by 2 equals 8/16 and divide that by 2 equals 4/8, and divide that by 2 equals 1/2 of an inch.

Reading the body upper major scale we see that 31/64 is 12 + something mm.

If I change the digital reading to millimeters, I see 12.36mm on the display.

Reading the body lower major scale we see that 31/64 is 4 + something, very close to 5, but I see 0.4865 inches on the display.

This caliper is not a precision scientific instrument costing hundreds of dollar.

It is made off shore and I am not sure what the guarantied plus and minus accuracies are for millimeter and decimal equivalents are.

I am telling you this because the next time I set the caliper to read 31/64, it displayed the millimeter reading as 12.44mm and the decimal equivalent as being 0.490 inches.

I am really not interested in what they are exactly - I use the fractional display most of the time for working with wood.

I am sure I could rub the piece of wood against my beard and get another reading.

Remember each dial caliper and digital caliper must be zeroed prior to making a measurement.

On the digital caliper it is pretty easy, close the jaws and push the ZERO button an you are good to go.

On the dial caliper, you must close the jaws and to the best of your ability rotate the dial so that the indicator is reading ‘0’.

There you have it, how to read a caliper.

Udie