Wulf's Webden

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Lining up and reading


I recently set up an order of a couple of things from CPC Farnell but was just under the amount needed to get free delivery, so I decided to add in a set of vernier calipers which I was eyeing up a few months ago. I was tempted by a digital pair but, in the end, opted for a plain steel; durable, time-tested and they won’t need new batteries from time to time.

Calipers are a tool for accurately measuring distances and transferring those measurements from one place to another. The simplest forms are just a more precise method of measuring with your fingers on one piece and trying not to move them as you move to another piece. Many calipers also come with scale markings so you can read off the measurement and write it down. What Pierre Vernier figured out in 1631 was a way to add precision beyond what could be accomplished by the naked eye by means of a second scale.

I did a quick bit of revision today and brushed up on how to make that reading with a website and the video below. The quick reading can be done based on the zero point on the lower scale and gives the precision of any other ruler, although you can’t easily get a ruler across or into some of the gaps you might want to measure. The trick is the that the lower markings only line up perfectly with the upper markings at one point. In the image below, I can estimate that will be about halfway between 29mm and 30mm. Looking along (and within the limits of the resolution), I’d be inclined to say that comes one mark after the 5. Each marking represents .02mm, so the final reading would be 29.52mm.

Of course, I can’t cut with that degree of accuracy, so this will be overkill for much of the woodworking I do but I think I’ll find some uses for it and it will, in a small way, make certain tasks just that little bit easier.

Reading Vernier Calipers

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