PAGE 11 — CALIPERS

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PROFESSIONAL REPAIRS & SALES IN THE U.S.A. SINCE 1959

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Dial Calipers — Digital Calipers — Vernier Calipers

For what it's worth

Dial calipers are like vernier calipers with a dial. This makes it easier to read for some people. The vernier scale can be small and you may have to resort to glasses or even a magnifier to read your vernier. The dial is pretty large and you probably won't have to squint to take a reading. While dials may be an advantage, it causes all sorts of problems. For one, all those gears and parts will eventually malfunction. Count on it.

For another, having a dial limits the calipers to being either metric or inch reading. That's no problem if you never need to switch systems. One or two models have attempted to combine both systems on one dial but that's confusing and bound to lead to errors.

Dial calipers offer four measuring capabilities: outside dimensions—such as diameters—measured with the large jaws, inside dimensions measured with the smaller jaws, depth measurements obtained with the extending rod, and step measurements taken with the front of the tool.

An optional Centerline Accessory Kit will also allow you to easily measure distances (center to center) between holes, groove diameters and undercuts where the jaws alone would be unable to reach.

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Before we start, let's state outright that the best, most reliable, and most useful caliper you can own is a vernier caliper. It isn't electronic and it doesn't have a dial. Only seasoned pros are likely to own and use the vernier calipers. That said, let's talk about the more popular dial calipers...

The ends of the jaws are beveled so that measurements in slots and grooves are possible. Don't use this area of the jaws for general measuring however, because it wears down quickly. Measure with the flat area of the jaws whenever possible.

We used to advocate against getting calipers with carbide jaws but have had second thoughts. The calipers that come for repair always have badly worn jaws and the user rarely sees this as a problem. It is a problem: it can easily mean errors of .001" or more. However, carbide jaws have the disadvantage that they will chip easily, this being the nature of carbide. Broken carbide jaws can not be repaired. Particularly vulnerable are the sharp tips on the ID jaws. If you think that you can be reasonably careful, then we suggest investing in carbide jaws for more reliable readings.

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The depth measurement is fine for small diameter holes and can extend all the way to 6 inches. If you need to span a larger diameter hole you can always get a depth bar attachment which will make your caliper function somewhat like a dial depth gage (see below).

Calipers have .001" graduations and are accurate to ± one graduation (per 6") if none of the measuring surfaces have been worn, bent or damaged. They're perfect for all sorts of quick measurement and can be used as a preliminary source before moving on to more sensitive tools such as micrometers (.0001"), depth gages or dial indicators (.0005" and .0001").

Calipers should be frequently checked for accuracy using a gage block, or gage block combinations. To check for wear in the jaws do this: clean them and close them. Then hold them up to the light and if they're worn you'll see light shining through the gaps. At this point, measure with the unworn surfaces or have the calipers repaired. These jaws can be ground flat again. See calibration instructions on page 7.

The most common dial calipers have a measuring range from zero to six inches. These are the most useful because they can be easily handled. However, 8-inch, 12-inch, and even longer calipers are available. Be advised that it is nearly impossible to take readings near the end of the ranges of these calipers. They become awkward and clumsy to use. On a 6" caliper any readings above four inches are likely to cause you trouble. You should use the next larger calipers in these cases.

The inclusion of the dial makes for much easier reading because it eliminates the need to know how to read the vernier scale. The invention of the vernier scale is one of the unsung innovations of the past, but reading the scale requires some training and a lot of practice if you want to be proficient at it. It's best to ask someone to show you how to do this.

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When taking a measurement, close the jaws only lightly, with pressure that is consistent from one reading to the next. You'll soon see that it's possible to fudge the results by just pressing a little harder. You don't want to do this. If you're new to calipers, it may be a good idea to practice on a gage block for a while to make sure you can get repeated measurements.

For quick reading, combine the numbers in A-B-C order, as shown. (1.370" is the correct answer.)

By the way, is it caliper or calipers?

The usage is usually in the plural: a pair of calipers. As such, it will use the singular verb: a pair of calipers is indispensable.

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So you want to read fractions?

Are you smarter than the average 5th grader? You will still find vernier calipers with fractions of inches and learning to read them requires more math than skill. It's easy to make errors, but here goes:

Look at the zero on the upper scale. Take note of the line which it has just passed on the lower scale. These indicate 1/16 of an inch. For example, it may have just passed the 1-1/16" mark. Now find the spot where the upper and lower scale lines coincide. At this point, the upper line will indicate how many 1/128ths need to be added to the 1-1/16". If this is the number 4, for example, you will have to add 4/128" to 1-1/16" ... we'll leave you to do the math although we believe it adds up to 1-3/32".

Starrett makes it easy by printing the fractions directly on the dial. It is the ideal solutions for wood working and other inch reading applications. One caveat: This Starrett model 1202F-6 dial caliper is made in China.

Q: I am trying to locate a quality set of 6 inch digital fractional calipers. I have found a caliper from Fowler, SPI, Wixey and others. Mitutoyo and Starrett don’t offer one. All the reviews I’ve found on every company's calipers are mixed and contradictory. I don’t know what to believe. I would be using the calipers for woodworking, table saw set up, drill bit sizing and light metal work.

  • We have never encountered a fractional digital caliper possibly because most of our customers work in decimal inches with metal. The brands that you mention are inexpensive Chinese imports and since they appear to be the only options for you, we would go with the SPI. If there is any warranty issue, it would be more convenient for you to contact SPI to resolve it.

Measuring large diameters

Large diameters, say 10" are not conveniently measured with calipers. The jaws would have to be at least 5" long and holding a large caliper is a two-person job.

It would be better to use a micrometer. Any micrometer would have a throat depth large enough to measure the diameter of a rod within its range. And, you can probably do it without anyone else's help.

Where are they made?

It should come as no surprise that "made in…" doesn't always mean the entire gage has that country of origin. In fact, we can pretty much assume that at least some parts of ALL calipers will have Chinese origins. [If any manufacturer can prove otherwise, please let us know!] By Swiss federal law, for instance, a gage can be labeled "Swiss", or some variation of it, as long as at least 60% of the material is of Swiss origin and that final manufacturing was made in Switzerland.

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