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Calipers


This section will mainly deal with vernier calipers. Since the other types of calipers are pretty simple to use (ie read a dial or a electronic display) and the majority of people will have a difficult time learning how to reading a vernier.

Vernier scales on measuring tools were created by French Mathematician Pierre Vernier, he created a scale that was slightly off the standard scale, generally for a 25 thou reading scale its 1.225 long for all 25 positions giving each spacing 49 thou between them, as compared to the normal scale which generally has 25 and 50 thou spacing. This allows someone to approximate the difference by the ever so slight change of the position of the best matching vertical combination of the scale's line pattern to the Vernier scale.

Metric scales usually use a .9mm spacing. Although sometimes difficult to see, the best way to do is is to approximate the value by comparing ones that appear to look the same on opposite ends and find the middle, if there are a few lines that appear to be aligned right.

I made this caliper up using Autodesk Inventor originally to help students in the T121 program that I was a Shop Assistant for one of the shop teachers last semester (I got exempted from the course due to already taking Tool & Die). This is the original pictures I used as a extra help sheet for the students. Hopefully my examples here will be as clear on the website as they were when I used these in person.

Everyone loves money, and everyone knows how to count change, so we can make the analogy to money, I have found it helps when you can apply a previously learned skill to a new one. 

Therefor if we think of our calipers as money we have the number of 10$ bills in our wallet (our inches), we have our dollars (our tenths of a inch, or 100 thou), we have our smaller 25 thou divider lines which are our quarters and we have our vernier scale that will give us the number of pennies we ended up with after buying one too many coffees from Tim Hortons.

Example 1


As you can see, on this scale, our zero on the vernier is at the zero line of the scale. Now to confirm that the calipers are indeed close we shale look at the 25 mark on the vernier, which does line up. Therefor we now know that our caliper is closed, and does not have any dirt in it that will impede our ability to use it as a measuring tool. Remember cleanliness is next to godliness.

Example 2:


Now this one is a little more difficult, although we cannot see how far visually the calipers are open, it does not matter, if you notice on the measurement scale we are somewhere before the 4 inch line, therefor we are measuring a 3.XXX inch part. Now that we know that we look at the zero on the vernier scale, as you can see we are past the 6, but not passed the large line in the middle of the 6 and the 8, which is the 7. 

Now that we count our quarters, we are 3 lines passed the 6, therefor we have 75 cents in quarters. So our size right now is 3.675", now we must count the pennies on the vernier scale. If you look closely you'll see that 11 and 12 look to be both aligned. Therefor our measurement is approximately 3.686.

As you can see I didn't split the number in the middle and chose the smaller of the 2. Reason being a caliper is not a tenth instrument, or is it really a measurement instrument to read accurately to the thou. 

Don't believe me? Take your calipers and wiggle the slide, you'll notice you can actually move it up and down a bit. That gives us error therefor we cannot be sure that the jaws of the caliper are actually properly aligned or not. Personally if I require anything better then +/- 5 thou I always go to micrometers. Others may disagree however.

Example 3:


Now for this one, we can see that our 3 inch marker on the scale is to the right of our zero, so we are measuring a 2 inch part. We are also past the large unmarked line between the .8 mark and the 3 inch, therefor our measurement is 2.900" so far. Then we look at the number of quarter lines, we are past the 2, which means we have 2 quarters.

Our number therefor becomes 2.950". And when looking at the scale, again for  the best aligned line. It appears to me that the 9 thou and the 7 thou lines are misaligned about the same, and the 8 thou line is straight. Therefor our measurement is 2.958".

The next 3 examples as for you to work out, at the bottom of this page I will include the answers for them.

Good luck!

Example 4

Example 5

Example 6:



So how did that go? Well the answers for
Example 4 is .568 inches,
Example 5 is 3.373 inches
Example 6 is 1.110 inches.

Included as a attachment is the GGG-C-111C Vernier Caliper specification sheet.
This outlines the military specifications for Vernier calipers.
 
Dimitrios Simitas
Note you may wish to click on the pictures while reading the vernier scales. Due to the distortion of scaling them. But by clicking the pictures you will see the full size picture that is easy to read.
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Dimitrios Simitas,
Feb 27, 2010, 10:45 PM
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