Smart Manufacturing and Tolerance-Based Machining

Industry 4.0 is a term you are probably familiar with—the impending arrival of smart factories, with data-driven production equipment that will signal the 4th revolution in manufacturing technology.

This manufacturing utopia is automated and responds in real time to process challenges such as an out-of-tolerance part. The equipment would not only identify that the part is out-of-tolerance, but also conduct a root-cause analysis before developing and implementing a solution. While it does this, the equipment is broadcasting to downstream stations that there is a delay in the machining process.

On some scale, this is possible today with the help of in situ probing cycles and macros that update registers in a CNC’s control software.

But to be considered smart, I would expect the equipment to anticipate an out-of-tolerance situation and hedge against the defect before it ever exists. For this scenario to come to fruition, several prerequisites must be met—for example, the machine tool must collect data that signals an impending defect. This might show up as an irregular pattern in a servo motor’s torque curve, or the machine base vibrating at a resonant frequency.

In the timeline between the third and fourth Industrial Revolutions, we are at the stage of knowing what needs to be done, and actively working to meet the many “prerequisites” like those above. And this is where tolerance-based machining enters the picture.

On the road toward machine tools that can predict inspection failures, we must first reach a point where software understands what a tolerance is, how to read it, and how to target it.

And it just so happens that SOLIDWORKS CAM’s feature-based approach provides the necessary structure for tolerances to be presented to the manufacturing software (in this case, it is the software creating cutting paths).

In SOLIDWORKS CAM, which is powered by CAMWorks, the fundamental unit is a feature. There are many types of features, and the software understands how they differ from each other:

SOLIDWORKS CAM Milling Features

  • Pocket
  • Slot
  • Corner Slot
  • Boss
  • Hole [Counterbored/Countersunk/Threaded/Multi-Stepped]
  • Open Pocket
  • Face
  • Perimeter
  • Open Profile
  • Engrave
  • Curve

In milling, SOLIDWORKS CAM recognizes several parameters about each of these features:

  • Is the shape circular, rectangular, obround, irregular or wrapped?
  • Is it blind or through?
  • Does it have a flat or a radiused bottom?
  • What is the stock material?
  • What is the overall size, depth, and largest inscribed circle?

So SOLIDWORKS CAM features are “smart” in that they are packed full of data ready to be leveraged.

Today we rely largely on experienced CNC programmers to interpret the dimensions of 2D drawings and devise a plan for machining. Instinctually programmers assess their parts for machinable features, weigh the significance of the parameters above, and then develop a strategy to cut the feature. The success of this process is a function of the programmer’s experience.

However, in SOLIDWORKS CAM, a strategy is suggested to the programmer based on the feature’s parameters and what the programmer has successfully done in the past. This is called knowledge-based machining and, when implemented right, it reduces programming time tremendously while increasing quality.

But what about tolerances? That criteria wasn’t listed above and it may be the single most significant factor when choosing how to cut a part! The same physical feature will be cut differently if its tolerance is +/- 0.010 inches vs +/-0.0005 inches, so in order to get to where we want to be (fully automated manufacturing), the tolerance must be considered.

The good news is that both SOLIDWORKS CAM and CAMWorks can add tolerance windows to their criteria for strategy selection. This is a major milestone toward smart manufacturing, and while the technology is still in its infancy, it is very promising.


DimXpert is now known as MBD Dimensions. (SOLIDWORKS 2019.)

Beginning with the SOLIDWORKS 2019 release, the tool set formerly known as DimXpert is now MBD Dimensions. Not to be confused with the SOLIDWORKS MBD module, this technology is part of the core SOLIDWORKS install and is available to all users. MBD stands for Model-Based Definition.

MBD Dimensions are part of a broader category known as product manufacturing information (PMI). PMI is information critical to the manufacturing of the part (such as tolerances) that is embedded in the 3D file.

By adding PMI to the 3D CAD file, companies are enabling a paperless workflow. Not only are drawings costly to create, they oftentimes don’t even match the 3D model. Government, education and professional industries are united in their movement away from 2D drawings, and SOLIDWORKS has been working hard for years to make that a reality.

MBD Dimensions can be mundane size or location tolerances, or they can be more complicated GD&T type tolerances.

SOLIDWORKS Geometric Tolerances

  • Straightness
  • Flatness
  • Circularity
  • Cylindricity
  • Profile of line
  • Profile of surface
  • Parallel
  • Perpendicular
  • Angularity
  • Circular runout
  • Overall runout
  • Position
  • Concentricity
  • Symmetry

Millions of parts are made every year with simple basic dimensions and tolerances, and they work. But the industries that are pursuing Industry 4.0 ideals the hardest make extensive use of GD&T. Therefore, in order to be relevant for a longer period of time, CAM tools seeking to incorporate tolerances into their workflow must be able to interpret GD&T, and the CAMWorks version of this technology does just that. In addition to the GD&T information, CAMWorks TBM can also interpret ISO286 codes commonly seen in shaft and bore drawings, as well as surface finish callouts.


In SOLIDWORKS CAM, the tolerance-based machining (TBM) tool works much like the regular automatic feature recognition (AFR) feature but also considers tolerance window. Every feature type can be setup with a limitless number of separate tolerance window strategies.

For example, the regular AFR might be setup to choose a “drill” strategy for any hole it finds. When AFR finds a hole, regardless of any tolerance callout that might exist for that feature, it will center the drill and then drill the hole. Done. It is left to the programmer to decide if that is an adequate strategy based on the tolerance callout that (hopefully) exists outside of the 3D model.

When TBM is used, that same hole (with an attached tolerance) would be found and a strategy that matches the level of precision needed would be automatically suggested. A hole with a tolerance window of only 0.002 inches might be assigned the “ream” strategy, while a hole with a wide-open 0.020-inch window could be assigned “drill only.”

Holes are the simplest application for this technology, and TBM handles these features very well. As features become more complex and the type of potential tolerances expands, TBM becomes less foolproof but still worthwhile.

This is a journey, and SOLIDWORKS sees the massive upside for strong tolerance-based machining capabilities. As we’ve discussed, it’s a critical prerequisite to the smart manufacturing of tomorrow.

It’s Not Just Milling

We’ve based this discussion on a milling example, but SOLIDWORKS CAM and TBM will also handle lathe parts. SOLIDWORKS CAM Professional knows several different types of turn features:

  • Outer diameter
  • Inner diameter
  • Groove
  • Face
  • Cut-off

Each of these features are tracked in the technology database (TechDB) the same way the milling features are. SOLIDWORKS CAM recognizes turn features and suggests an appropriate strategy to the programmer. And if a feature carries a tolerance, TBM will account for that, too.

The technology database (TechDB) retains best practices and allows the programmer to easily revisit successful machining strategies.

Taken one step further, multi-tasking machines that combine both milling and turning on the same platform are also supported, but only in the CAMWorks product line. There, we can program and sync up to four tool turrets and both a main and a sub-spindle.

Where Do We Go From Here?

In my opinion, SOLIDWORKS TBM is primed to play the role of “tolerance interpreter” in the grand scheme of Industry 4.0 manufacturing. I’m not aware of any other tool that is doing what TBM does, and it has room to do so much more.

Not all tolerances are symmetrical, and not all 3D models are drawn to nominal dimensions. A robust TBM technology will perhaps accommodate for this by altering the side allowance of the feature. Currently, this is done manually by the programmer but there is little to stop SOLIDWORKS from automating this process.

The Move Feature tool allows programmers to work with 3D models that are not drawn to nominal size.

Another potential automation is the moving of features in XYZ space. If a part has a better chance of passing inspection if the features were cut slightly differently than how the 3D model was drawn, then the programmer can move the CAM feature (without altering the underlying CAD). I’m certain that TBM will eventually automate this process and take advantage of bonus tolerances born out of the GD&T that human programmers failed to spot.

Between MBD Dimensions, SOLIDWORKS CAM TBM, and other upcoming technologies, the world for a SOLIDWORKS user is looking very smart—and very paperless.

If you haven’t explored SOLIDWORKS TBM, or SOLIDWORKS CAM in general, I highly encourage you to do so. It is installed and available to all SOLIDWORKS users who are currently on subscription.

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