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By Andrew Batchelor
This web page was last updated on July 23rd, 2016
Calipers range in price
from a few dollars
to $50 or more, depending on the material, accuracy, and readout type
On the cheap end,
There are three styles of caliper, named for the way they give a reading. Vernier calipers rely on a scale etched into the body, with good eyesight required to determine the actual measurement from an increasingly smaller set of lines. Dial calipers have a stopwatch-like face that indicates the measurement using a pointer. Digital calipers have the advantage of giving a direct reading in numeric form; some convert between millimetres, and inches (decimal and/or fractional) at the push of a button.Measurement Possibilities
Most calipers are accurate to 1/1000th (0.001) of an inch, or 1/128th when using fractional measurements, and 0.01mm (0.00001m or 10 microns) in metric. Note that micrometers are 10 times more accurate, but this is rarely needed unless you are machining your own live steam engine parts.
There are four basic
measurements that can
be taken with a caliper: inside, outside, depth, and off-set or step.
geometry of the caliper also makes it possible to transfer
because on most calipers, these four lengths are always equal. See
Obtaining accurate, consistent readings depends as
on proper technique even more than the quality of the measuring tool.
Make sure the
are clean and free from dust or grit.
Using the caliper without turning it on…
One of the biggest sources of error in building occurs when a measurement is taken and then recreated at a later time. Locking the head of the caliper at a given measure, and transferring it to another site, rather than re-measuring is the simplest way to avoid this discrepancy. Remember that all four measurements (above) are always equal, allowing transfer between types of measurements as well. E.g. Take the diameter of a dowel using the outside measure, then verify that the receiving hole is big enough using the inside measure.
Care & Feeding
The more expensive
calipers are precision
a Caliper –
Go to http://www.leevalley.com/en/home/Articles.aspx?p=32 and use the link to "Measuring". This section also has a number of additional items of use to modellers.