In the broader world, we are all familiar with rough versus smooth surfaces. In the world of metrology, surface roughness refers to the texture of a particular surface. When working in different industries, depending on the task at hand, you may be required to work with surfaces of specific textures. There are a lot of reasons why you might want a particular degree of roughness or smoothness and because of this, it is important to have a reliable way to measure these dimensions. This leads us to the surface roughness gage. The surface roughness gage does not only measure surface roughness generally, but it can be specialized through the use of optional probes in order to conduct even more precise and accurate measurements.
Introducing the surface roughness gage
A surface roughness gage is a tool used to assess the surface texture of a material. The main measurements taken using a surface roughness gage include the roughness depth and the mean roughness value, which is reported in micrometers or microns. These tools are an easy way to determine the high-frequency, short-wavelength content of a particular surface. While there are a variety of tools to use when assessing surface roughness, the surface roughness gage is sensible due to its transportability and ease of use. These useful tools are a great way to measure the micro-irregularities on a given surface. Knowing the roughness of a surface is ultimately important for determining the suitability of a particular surface for its intended purpose.
Measuring roughness does matter
The roughness of a particular surface plays a role in how that surface interacts with other surfaces. When you are building a machine, a part, or even another tool, it is necessary to take into account how the surface of the machine, part, or tool will interact with other surfaces in its broader environment. For example, a rougher surface will wear out more quickly than a smoother surface, create a higher friction coefficient, and be more susceptible to corrosion. Additionally, a rougher surface may create more potential adhesion than a smooth surface. Understandably, knowing the degree of all of these factors will influence the eventual functionality of what you are building or measuring.
How roughness is measured
Roughness gages or testers use a mechanical tip to trace the linear changes across a determined line, thus picking up on any rises or falls along the ideal line of smoothness. There does exist sophisticated technology that uses an aerial measurement of an entire surface through the use of optics, lasers, or interferometers. However, this level of specification and technology is not always necessary. This is where the typical surface roughness gage comes into play. This tool will take the average absolute deviation from a central line on the surface being measured (known as Ra), the root mean square of the deviation (known as Rq), and a number of other measurements of peak heights and valley depths into account to report a final roughness measurement.
Surface roughness gages come with a selection of optional probes
Yes, that’s right, surface roughness gages have optional probes. Commonly used interchangeable surface roughness gage probes include: a general purpose probe, a small bore probe, a groove bottom probe, a traverse chisel probe, and a parallel chisel probe. When you purchase a surface roughness gage, it will come equipped with a general purpose probe. For most measurements of surface roughness, the general purpose probe will be adequate. However, under specific measurement contexts, you might need one of the alternative surface roughness gage probes to more accurately and precisely take a measurement of the material roughness. When working with bores, sharp edges, “O” ring grooves, recesses, sharp edges, or small outer diameters, your will get a better measurement when implementing a more targeted type of surface roughness gage probe.
Available optional probes for surface roughness gages
Surface roughness gage – general purpose probe
A general purpose probe is often the standard probe provided for surface roughness gages. Used for most surface roughness applications, the general purpose probe has a wide application and will be suitable for typical measurements of surface roughness. Commonly seen dimensions will be a 90° conical diamond stylus paired with a 0.0004″/10μm radius per ISO specifications or a 90° conical diamond stylus paired with 0.0002″/5μm radius per DIN standards.
Surface roughness gage – small bore probe
A small bore probe is ideal for measuring the surface roughness of small holes or bores. Typically, when using a small bore probe, you will be measuring a bore that has a minimum inside diameter of 5.0mm and a depth of up to 15.0mm. Commonly seen dimensions for surface roughness gage small bore probes will be a 90° conical diamond stylus paired with a 0.0004″/10μm radius. A 0.0002″/5μm radius is also often paired with a 90° conical diamond.
Surface roughness gage – groove probe/groove bottom probe
A groove bottom probe, also known as simply a groove probe, can be attached to a surface roughness gage when completing measurement of the bottoms of “O” ring grooves, recesses, and holes with a depth up to 6.0mm. A surface roughness gage should be outfitted with a groove probe when looking to assess short lands and shoulders. The groove bottom prove usually has the dimensions of a 90° conical diamond stylus paired with a 0.0004″/10μm radius.
Surface roughness gage – traverse chisel probe
A traverse chisel probe ought to be applied in the context of trying to gage roughness along sharp edges or on small outer diameters where the probe needs to be aligned at wither a high 180° or in a more closed position of 90°. The 180° and 90° diamond chisel stylus is commonly paired with a 0.0004″/10μm radius for traverse chisel probes on a surface roughness gage.
Surface roughness gage – parallel chisel probe
A parallel chisel probe is what you will want to attach to a surface roughness gage when you are gaging sharp edges or small outer diameters and you will require the probe to be perpendicular to the traverse axis, either in a 90° or a 270° position. The typical parallel chisel probe is built with a 90° diamond chisel stylus that is paired with a 0.0004″/10μm radius.
Benefits of using the different optional probes on a surface roughness gage
As with all of metrology, any particular measurement is best completed using a tool specified for that purpose. There are some very well made generalist tools, and many tools, such as the surface roughness gage come with a general purpose application part. However, when completing more particular measurements or under confined as well as unusual circumstances, a tool extension built for a specified purpose can be indispensable. Different optional probes vary based on design and size. Having the correct type of surface roughness gage probe will make a difference if you are measuring a standard sheet of metal versus a bore in concrete. The radius of a particular surface roughness gage probe is important in determining the contact force. A smaller probe radius results in a lighter required force. Depending on the type of material you are working with and the type of surface you are measuring the roughness of, using the proper optional probe has the major benefit of improving the accuracy of the measurement output as well as the safety of the material.
Conclusion
Some industries will be more impacted by surface roughness than others. However, understanding the role of surface roughness, how to measure it, and the different surface roughness gage probes available will help you to be prepared for any number of metrology situations. Your work may even be improved by taking surface roughness more into consideration than you are used to doing. The surface roughness of a material will greatly impact how that material functions. Browse the selection of surface roughness gage probes at Higher Precision today or contact our expert team to learn more about how surface roughness could be impacting your work.
FREQUENTLY ASKED QUESTIONS
- Why is roughness important to measure?
The roughness of a surface has a huge impact on the functionality of that surface in a particular context. Mainly, the way in which one material will interact with another material depends partly on the surface roughness of each one. If you are working with a rougher surface (so a greater degree of bumps and divots), then you can expect that material to wear out more quickly than a smoother surface would. The higher degree of friction present when using rough materials as opposed to smooth materials is also an important consideration. This can result in higher adhesion, which may or may not be the effect you are looking for. Depending on the particular part, tool, or machine you are building, you will want a different degree of surface roughness and so being able to have an accurate measure of surface roughness will be very important.
- What different types of surface roughness gage probes are available?
The main types of surface roughness gage probes available include general purpose probes, small bore probes, groove probes or groove bottom probes, traverse chisel probes, and parallel chisel probes. Each of these types of probes is best suited for a particular kind of measurement. Many metrologists can get by with only ever using the general purpose probe for common surface roughness measurements. However, when working with more particular surface contexts, you will likely require the probe that is intended to be used in that context. When measuring surface roughness of small holes, you will want the small bore probe. When measuring surface roughness of the bottom of an “O” ring groove, a recess, or a hole with a depth up to 6.0mm, you might use the groove bottom probe. Traverse chisel and parallel chisel surface roughness gage probes are best used to assess roughness in a gaging sharp edges or small outer diameters, and differ the surface angle they are placed in.
- What are the benefits of the different types of surface roughness gage probes?
The central benefit of understanding and using the different types of surface roughness gage probes available is getting a better measurement. There are a number of measurements that can be completed using basic tools and the standard tool parts. However, when measuring surface roughness, you need to consider the context of the surface as well as the type of material being measured. Factors such as the design of the probe and the size of the probe radius will impact the accuracy of your surface roughness measurement as well as the safety of your material during the measurement process. Different surface roughness gage probe radii result in varying degrees of contact force. If you are looking for a lighter contact force, use a smaller probe radius. The shape of a surface roughness gage probe will be understandably different if you are gaging a flat surface as compared to a small bore as compared to a sharp edge. The benefit of having different types of surface roughness gage probes is that you are able to apply the proper tool to the proper measurement for increased precision and safety.
GLOSSARY TERMS
- Surface Roughness Gage
A surface roughness gage is a tool used to measure the texture on the surface of a material. By taking a measurement of the depth and width of different bumps and cavities, the surface roughness gage creates a mean roughness value and assesses both macro as well as micro-irregularities on a surface. This helpful tool is useful to determine the suitability of one material for a specific purpose based on the present roughness across the surface. The surface roughness gage comes with interchangeable probes that can be switched out depending on the intended use.
- General Purpose Surface Roughness Gage Probe
A general purpose surface roughness gage probe is the most commonly applied probe type to measure surface roughness. When conducting typical measurements of surface roughness, the general purpose probe will suffice. Common dimensions: 90° conical diamond stylus with 0.0004″/10μm radius per ISO specifications or 90° conical diamond stylus with 0.0002″/5μm radius per DIN standards.
- Small Bore Surface Roughness Gage Probe
A small bore surface roughness gage probe is meant to measure the surface roughness of a small hole with a minimum inside diameter of 5.0mm and a maximum depth of 15.0mm. Common dimensions: 90° conical diamond stylus with 0.0004″/10μm radius or 90° conical diamond with 0.0002″/5μm radius.
- Groove Bottom Surface Roughness Gage Probe
A groove bottom surface roughness gage probe is meant to measure the surface roughness of the bottom of an “O” ring groove, a recess, a bore with a depth of up to 6.0mm, short lands, or shoulders. Common dimensions: 90° conical diamond stylus with a 0.0004″/10μm radius.
- Traverse Chisel Surface Roughness Gage Probe
A traverse chisel surface roughness gage probe is meant to measure surface roughness when working with sharp edges or small outer diameters. The traverse chisel surface prove is ideal for alignments of 180° or in a more closed position of 90°. Common dimensions: 180° diamond chisel stylus with 0.0004″/10μm radius or 90° diamond chisel stylus with 0.0004″/10μm radius.
- Parallel Chisel Surface Roughness Gage Probe
A parallel chisel surface roughness gage probe is meant to measure surface roughness when working with sharp edges or small outer diameters. The parallel chisel surface prove is ideal for perpendicular alignments to the traverse axis of a 90° or a 270° position. Common dimensions: 90° diamond chisel stylus with 0.0004″/10μm radius.