Gaging Specifications often require inspection of dimensional relationships between two features, or between two dimensions on the same feature.

When you think about it, a lot of data has become available to the process engineer on the shop floor. Starting 50 years ago with in-process charting, data has grown exponentially with the digital rev

Thickness is one of the most frequently measured dimensions, and also one that is very easy to understand. So you might think that someone would come up with a one-style-fits-all measurement approach good for just about every kind of thickness application, but it just isn’t so.

Sometimes we are faced with making critical inside diameter checks on parts that do not present themselves in a straight forward fashion. Usually these checks are on the inside of some type of bearing and they can be almost any size.

few months ago this column described the use of surface plates, observing that a flat surface is the basis for most dimensional measurements. Many workpieces, of course, are neither flat nor straight. In order to measure the angular accuracy or straightness of an angled surface using a surface plate, a sine instrument comes into play.

For many years now, the method of choice for low-volume, general purpose inspection has been surface plate work using test indicators and height gages. Recently, electronic height gages have made the layout inspection process a little more accurate.

If a workpiece has ever left your shop with an important dimension unmeasured because you couldn't get at it to measure it, you probably didn't know about indicating caliper gages.

Here are some the very many ways that a shaft might be inspected after manufacture in today's world. Many of these solutions are also fairly new to dimensional metrology:

About 30 years ago, the concept of data collection for process control took a major leap forward. This was about the time that a combination of electronic technology and economics allowed gaging to become digital.

A depth gage is a very common hand tool used to inspect the depth of holes, slots, counterbores, recesses or the distance from one surface to another. They are especially common in the tool and die industry. Like other hand tools, they have undergone a gradual change from mechanical scales to digital wonders.

Depth gages are among the simplest of indicator gages, typically consisting of an indicating device mounted through a reference bar or plate. Though they may be simple, depth gages are used in thousands of critical applications, to measure the depth of holes, counterbores, slots, and recesses, as well as heights or locations of some features.

When gaging with mechanical or electronic transducers, you can sometimes get more than you bargained for in terms of the results from the gage.

In this column we have discussed how most dimensional gaging applications are really just variations on four basic themes, to measure height, depth, thickness, or diameter.

There are many questions to ask when deciding what gage to choose for an application, but whether to bring the gage to the part or the part to the gage is one of the most fundamental.

Many of the gaging applications we've considered over the years involve size inspection of a single feature, e.g., the diameter of a hole, depth of a groove, height of a gage block, etc. Many parts, however, contain multiple features that establish dimensional relationships between two or more other parts.

Specifications often require inspection of dimensional relationships between two features, or between two dimensions on the same feature.

Virtually all metalworking shops need to measure holes, thicknesses, and heights. Some shops, however, have to perform measurements that are more limited in application: some are industry or even company specific.

Like phones and computers, today's bench amplifiers offer greatly improved performance, better displays, less power consumption and more data user capabilities. But what struck me in reviewing that old column was that most of the functions we were touting for amplifiers then are now available in digital indicators.

Producing precision spools and sleeves (e.g., for fluid pumps) and other pairs of parts with matching inside and outside diameters can be among the trickiest of quality issues.

By using harmonic analysis you can figure out what creates the lobing conditions on the part. There are three major contributors to the lobing condition.

As with any measurement, the quality of the result depends on the measurement instrument and the care with which the operator handles the measurement procedure.

It just might be easier to manufacture a groove on a turned part than it is to inspect it. Select the right cutting tool, set the CNC, and you're done, but because of the critical functional role played by grooves for seal rings and retainer rings, good gaging practice is a must.

Conical parts, such as machine tool tapers (i.e., tool holders), gas petcocks, and the shanks of modular prosthetic joints, must often be inspected for taper accuracy. This is usually performed with a special air or electronic gage, custom-made for the specific part.

A machined taper fit between mating parts is a fast and secure way to put two parts together. Fast mating and good alignment make taper fits critical in two very different fields. One that most machinists are familiar with is the taper fit that aligns the tool holder and spindle on a machining center.

In the world of manufacturing many small parts will not fit into the field of view on a standard viewing microscope, so external tools are added to expand measuring capability.

The human eye is a pretty good discriminator when it comes to determining size. When two objects are placed side by side, it's often fairly easy to see the difference in size simply by comparison.

The need for long range height measurements has been around since the principles of layout work became a fundamental requirement in machine shops.

Surface plates provide a broad, smooth, flat reference surface that can be extremely useful for inspecting incoming, in-process, or finished parts.

Machinists working strictly in metal-working shops do not have many occasions to gage the thickness of soft materials. But many of our readers work in supporting roles, helping to build or maintain the machines that produce textiles, plastic films, paper and other products that are compressible.

Temperature variation is one of the most significant sources of gaging error. As manufacturing tolerances get tighter and the margin for gaging error gets smaller, it becomes an issue that must be addressed.

The environment is often the largest contributor to measurement errors. Conversely, once the environment is under control, great strides can be made in improving the overall measurement process.

Depth gages are among the simplest of indicator gages, typically consisting of a short range indicating device mounted through a reference bar or plate. Though they may be simple, depth gages are used in thousands of critical applications to measure the depth of holes, counterbores, slots, and recesses, as well as heights or locations of some features.

No pun intended, but thread gaging has always seemed a rather convoluted subject to me. So, when I was questioned on the topic recently, I asked my friend, Lowell Johnson, a recognized authority and president of the Johnson Gage Company, to explain some of the basics and offer some tips on the process.

The flatness of machined planar surfaces is often critical to the performance of parts and assemblies. The plane is also the basis or reference for most dimensional and geometric measurements; including height, location of features, squareness, and datum’s.

Surface plates provide a broad, smooth, flat reference surface that can be extremely useful for inspecting incoming, in-process, or finished parts.

Balls are an integral part of every machine shop. They are found in bearings for both rotary and linear motion applications in machine tools; they act as contacts and pivot points in gaging equipment and tooling; and they serve as masters for both size and roundness gaging.

Many articles ago we discussed the terms "gaging" and "measuring," which are often used interchangeability. There are times when gaging is appropriate and others when measuring is the best way to go.

A DC motor is a device that converts electrical energy to mechanical energy. The conversion essentially happens between two major parts: the stator, the static part that holds the windings and receives the input power, and the rotor, the rotating part that brings about the mechanical rotations.