PAGE 12 — DIAL THICKNESS GAGE

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Dial Thickness Gage

dial thickness micrometer - medor de espesores

Quick and easy measurements of small parts and thicknesses are made with these hand-held tools. A choice of resolutions and physical dimensions is available from several manufacturers. It needs to be said, however, that dial gages are almost a thing of the past when digital readout is available. With a digital gage there is little likelihood of misinterpreting the reading on the dial. That said, here are some analog gages that might still serve a useful purpose.

The dial thickness gage is typically used to measure the thickness, in mils (.001"), of sheet metal, plastic, paper, and cardboard. Metric measurements (0.01 mm) are likely to be used for fabric thickness and numerous medical, botanical and biological applications. It's useful for measuring diameters of round and cylindrical objects, tubing and pipes. It will make quick work of determining the diameter of bolts, fishing line and guitar strings. Jewelers are likely to use it to measure the gage of gold wire. It has a lifting lever at the top which you depress with your thumb.

The measuring surfaces (anvils) are flat and parallel. These are used for round or cylindrical objects. Thickness of flat sheets is better taken with at least one of the anvils rounded. Replacing the upper anvil with a round nylon contact point will eliminate some of the danger of damaging glass. Again, various manufacturers offer different models.

Throat depth varies from a fraction of an inch to as much as 16 inches. This will determine how far the gage can be inserted onto the sheet or part being measured. Gages with large throat depths will require sturdier frames to eliminate distortion from weight.

The pocket thickness gage is a miniature version, easily tucked away. These are available with an accuracy of ±.001" or ±0,01mm making them suitable for many applications. This has a lever which you need to slide in order to raise the anvil. A quick and easy to read digital version is available which offers both inch and metric readings.

If you need the dimensions of larger items, use calipers instead. If you need greater resolution and accuracy you may want to use a micrometer. If you need to measure the thickness of coatings in mils or micrometers then use the Coating Thickness Gage available in several different styles.

The stated accuracy of the gage is more important than the dial graduations. Most digital instruments mislead with readouts to .00005" but offer accuracy of only ±.001". When shopping for a thickness gage ignore the graduations and focus on the accuracy instead.

As with other gages, the inexpensive models are not repairable. They should be tossed and replaced when needed. Better quality gages are more likely to be repairable because spare parts will be available. You may wish to inquire whether a particular dial thickness gage is worth repairing before you send it to a repair shop.

Measuring force is often an important factor when soft materials such as plastics and fabrics need to be measured. The measuring force will be listed in the manufacturer’s catalogs. In some cases, the manufacturer can modify the measuring force to your particular specifications, but this must be requested at the time of purchase and will undoubtedly result in longer delivery times. In the meter-kilogram-second system, the unit of force is the Newton (N), where 1 Newton = 100 gram-force = 0.225 pound-force.

Mitutoyo dial thickness gage

This is the full sized version with guaranteed accuracy, including model 7326S with .0001" resolution. All these thickness micrometers have flat lower anvils (ø.433") and flat upper contact points (ø.394") made of ceramic for longer wear. A thumb-operated lifting lever raises the indicator spindle. A full grip handle accommodates the other fingers of the hand. They are easy to use and the Mitutoyo models are almost always repairable.

You can easily convert some of the newest models of Mitutoyo dial thickness gages to accommodate left handed use. Model 7300 shown above, for example can be converted. We'll do it for you, if requested at the time of purchse. Please inquire if this is possible for the gage you’d like to order. Please note that the letter S has been added to some models. This merely indicates that they are the most recent model made in Japan.

These models are also available with a large 4.72" deep throat. (See page 209 for details.) Larger throat depths up to 16 inches are available from the reputable German manufacturer Käfer.

Be sure to check for discounted online pricing often 20-30% below list.

Measuring force is important for applications that involve compressible material such as fabric or foam. The minimum measuring force for these Mitutoyo thickness gages is given in Newtons (N).

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Mitutoyo 7300S

Range Throat Depth Resolution Accuracy Force Model No. Discounted Online Prices
.05" 1.18" .0001" ±.0002" > 1.5 N 7326S Check price and availability
.4" 1.18" .001" ±.001" > 1.5 N 7300S Special clearance $96.00
while supply lasts
1" 1.18" .001" ±.002" > 2.0 N 7304S Check price and availability
1" 4.72" .001" ±.002" > 2.0 N 7322S Check price and availability
10 mm 30 mm 0,01 mm ±0,015 mm > 1.4 N 7301 Check price and availability
20 mm 30 mm 0,01 mm ±0,025 mm > 2.0 N 7305 Check price and availability
20 mm 120 mm 0,01 mm ±0,025 mm > 2.0 N 7323 currently unavailable

Blade Anvil dial thickness gage

The following special models have a blade anvil and blade contact. The thickness of the blades are .039", the width is .256" and the height is .197"

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Mitutoyo 7315

Range Throat Depth Resolution Accuracy Force Model No. Discounted Online Prices
.4" .001" 1.18" ± .001" > 1.5 N 7316S $99.00
while supply lasts
10 mm 0,01 mm 30 mm ± 0,015 mm > 1.4 N 7315 check discount price
How to measure the thickness of a sheet of paper (as an example)

For a flat sheet of paper, use a thickness gage which has flat anvils, top and bottom such as model 7309 shown on this page. Before you take a measurement, clean the anvils with a bit of alcohol, then place a piece of clean paper between the anvils, let them rest together under their own force, then pull the paper out slowly. This polishes and further cleans the surface.

Now, with the paper removed, allow the gage to close. The hand (the pointer) will point to the twelve o'clock position, to zero. If the zero is slightly off, then you can rotate the bezel until the hand lines up with the zero, exactly. Now lift the anvil and repeat several times to make sure it always points to zero. This is called repeatability and should always be less than half a graduation.

Now lift the anvil and insert the paper. Let the anvil close down on the paper and slide the anvils a little bit so you find the lowest reading on the dial. At first, the readings will fluctuate a few graduations because you may not be working parallel with the surface. You'll eventually find the right spot where the hand no longer fluctuates. Take this reading (one line = .001" in most gages).

If the hand points to 31 then you have a thickness of 31 mils, or .031". If it points to 10 then the thickness is 10 mils or .010". Since the gage has an accuracy of ±.001" your reading is correctly stated as "10 mils plus or minus one mil." This, of course means that the actual thickness might be as little as 9 mils or as much as 11 mils. There is no way you can get around this fact. Now repeat the process with the same sample. Do this about 3 times to make sure you always get the same reading. If the readings are off, you're not holding or manipulating the gage correctly.

One more thing: a "mil" is not the same as a millimeter (mm). They are entirely different dimensions. If your gage is metric, and the graduations are 0.01 mm, then every ten graduations will equal 0.10 mm. The same principles outlined above will apply.

How to calibrate your thickness gauge

If the dial thickness gage has flat anvils, as most of them do, you will want to make sure they lie parallel when closed. Clean the anvils with alcohol as needed. The easy way to check this is to hold them up to a light and look for gaps. If there are no obvious gaps then set the dial to zero. At this point, insert a calibrated gage block between the anvils and check the dial reading several times. You should not be off by more than one graduation. If it is off, then make sure the block is lying flat and properly seated. Also make sure that the anvils—and the gage block—are very, very clean. It stands to reason that if the anvils are not parallel, you'll get a different reading on one side of the anvils. Use the gage block to test for this possibility.

If your thickness gage has a relatively short range, then one or two different size gage blocks should suffice for calibration. Choose one for the middle range and one for the far range. Of course, if you only use the thickness gage for some specific measurement, then choose a gage block with approximately the same dimension.

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