STEP-NC Turns Twenty. Is Industry Finally Ready For It?

In July, Lockheed Martin set out its work on persistent identifiers: discreet digital tags that give a part’s individual features a unique, unchangeable identity, so that a hole and every specification associated with it can be tracked through design, machining, inspection and sustainment. Lockheed Martin partnered with Northrop Grumman, then extended the network to Sandvik Digital Manufacturing, Seco Tools, Mastercam, Verisurf, Metrologic DCS, Hexagon, Renishaw, InnovMetric, PTC, Siemens, Mazak and Datanomix, so that every tool in the value chain can publish and consume the same identifier.

Weeks earlier, Sandvik Coromant published results from the Dig4ReMan project with GKN Aerospace Engine Systems, Chalmers and the Fraunhofer-Chalmers Centre. That work applied STEP AP242 and AP238 to build a neutral, model-based language for geometry, product manufacturing information, machining instructions and tool data across the repair of damaged turbine blades. Mikael Hedlind’s framing was precise: the point was not really to repair parts, it was to prove that design, machining, simulation and inspection data can flow between organisations, because once everybody speaks the same language, collaboration gets faster and clearer.

Both are genuinely significant. Both invite a question.

None of this is new.

The standard is old enough to vote

ISO 10303-238 is not an emerging technology. The first edition arrived in 2007, the current edition dates from 2022, a further edition reached draft stage in May 2026, and the research literature reaches back further still. Suh published a shop-floor programming architecture for STEP-compliant CNC in 2003. Nguyen and Stark set out the system architecture differences for STEP-compliant control in 2009. Rauch’s group demonstrated over a decade ago how existing commercial controllers could be adapted to conform.

The validation work is equally old. In 2006, a joint Boeing and NIST effort published a portability validation of AP238 Conformance Class 1 for 5-axis machining, authored by Sid Venkatesh, David Odendahl, Xun Xu, John Michaloski, Fred Proctor and Thomas Kramer. Hardwick and Loffredo later documented lessons learned from implementing AP238 with four CAM vendors and two controls across two 5-axis machines of different axis configurations, interpreting a single AP238 file for both. In 2013 a roadmap for STEP-NC-enabled interoperable manufacturing was published with much the same cast, Odendahl among them.

Then there is a demonstration that deserves to be far better known than it is.

At IMTS 2014, Boeing built a baseline machining process for a titanium mould part and sent it to Sandvik Coromant and ISCAR to improve. A range of CAM systems were used. All communication happened in STEP-NC. The result was a single digital thread for the part, one STEP-NC description carrying all three process options alongside models for the part, rawpiece and tooling, cut daily on an Okuma control in the show hall via STEP Tools’ interface. The reported outcome was a 15 to 30 per cent improvement in machining time, and the stated reason was not a clever algorithm. It was that the digital thread made it much easier for Boeing to reach the tooling and process expertise sitting inside its suppliers.

Read that again. Collective intelligence, demonstrated on a machine tool, in public, twelve years ago. The tooling knowledge was the ingredient that made it work, and the thread was what made the knowledge reachable.

David Odendahl has been pushing this at Boeing for the better part of two decades. And yet, in subtractive manufacturing, the digital thread still has not reached technological maturity. Only a small number of machine tool OEMs have developed STEP-enabled technology at all. The overwhelming majority of metal in the world is still cut from ISO 6983 G-code, which carries coordinates, feeds, speeds and a tolerance band, and none of the contextual information that would tell a machine what the feature is or why it matters.

So before anyone gets excited about a new capability, the honest question is why it did not take, and what is actually different now.

Why it stalled

I have some skin in this. Several years ago, at the AMRC we investigated how to get contextual information via STEP-NC onto Siemens controllers, and we spoke at length with Boeing about it at the time. The obstacles we hit were almost entirely structural rather than technical.

The chicken and egg problem is real, and it is nobody’s fault. No manufacturer will restructure a programming workflow around a standard their controllers cannot consume. No controller builder will fund consumption of a standard nobody is sending them. Both positions are individually rational and jointly fatal. This is precisely why Rauch’s adaptation work and STEP Tools’ controller interfaces mattered so much, and also why they remained demonstrations.

The post-processor is not a defect. It is a business. The received story is that the post-processor is legacy friction to be engineered away. In practice it is where machine-specific knowledge lives, and where builders, integrators and CAM vendors differentiate. STEP-NC proposes to move that knowledge into a neutral file anyone can read. Asking an industry to standardise away its own differentiation is a commercial request wearing a technical costume. 

Interpretation was the hard technical problem, and it is the interesting one. The reason a Boeing and NIST team had to formally validate that tool centre programming was portable across two 5-axis machines is that portability is not automatic. Hand the same feature description to two controllers and you get two different cuts, because each interprets it through its own kinematics, drive limits and smoothing algorithms. G-code has the perverse virtue of failing predictably: it is machine-specific by construction, so nobody is surprised. A neutral file promises portability, and then the machine has the last word anyway.

It belongs to nobody. STEP-NC sits between CAD, CAM, controller, tooling and metrology. No single budget owns all five, so it lands in the gap between them, which is where good standards go to be admired.

Which makes the most interesting recent development in this space not a standards committee at all. In 2023 ModuleWorks stopped waiting and published MDES, the Manufacturing Data Exchange Specification, as a free and open format for describing manufacturing equipment: tool components, assemblies, fixtures, stocks, setups and how they mount in the machine, aligned with existing standards including ISO 13399. Autodesk and DN Solutions adopted it almost immediately, followed by PTC, SolidCAM, CHIRON, Cimsource and BobCAD-CAM. Yavuz Murtezaoglu’s stated reasoning was refreshingly commercial: everyone was paying to build and maintain custom bridges between systems, and a shared description removes that cost for all of them.

Two years of adoption against twenty is a result worth sitting with. It suggests the route through this problem may be a vendor with something to lose publishing an open specification and giving it away, rather than a committee producing a superior one and waiting to be adopted. Not because the engineering is better. Because somebody owned it.

What actually changed

Model-based definition stopped being an aspiration and became a procurement requirement. When primes tag features with persistent identifiers and expect the supply chain to consume them, carrying that richness downstream is no longer voluntary.

Everyone is building AI assistants on manufacturing data, and discovering the assistant is only as good as the structure underneath it. A copilot that can read a tolerance is worth considerably more than one that can read a coordinate.

And, bluntly, consolidation. In 2014 that IMTS demonstration required Boeing, Okuma, Sandvik Coromant, ISCAR and STEP Tools to align. Today a very large portion of that chain, CAD, CAM, post-processors, cutting tools and metrology, sits inside a handful of groups rather than dozens of companies. The coordination problem that stalled STEP-NC adoption for twenty years has become, in places, an internal roadmap question rather than an industry negotiation.

It’s all about context

The digital thread has become genuinely good at carrying three kinds of information down to the machine tool.

Identity is which feature this is. That is what a persistent identifier contributes, and it is the newest of the three.

Intent is what the designer requires of that feature. The tolerance, the finish, the datum scheme, the reason it matters.

Context is everything a machine needs to know in order to act on the first two: the machining type, the toolpath geometry, the tool and the rawpiece, and what a stated tolerance actually means for this operation rather than in the abstract. This is the layer STEP-NC was built to carry and the layer G-code structurally cannot. Strip context out and a tolerance is just a number in a header.

MDES is worth looking at again here, because it is the clearest evidence that the industry has recognised the context gap and is actively closing it. It describes the equipment side in detail: what tool is in which holder, in which fixture, mounted where, against which stock. That is real context and it removes real setup error. And it stops exactly where every description of a machine stops. It tells you precisely what is on the machine. It does not tell you what the machine will do.

Get all three onto the shop floor and a feature arrives tagged, toleranced and fully described in its own terms. That is a real achievement, and it is what twenty years of standards work bought.

What none of the three can tell you is behaviour. Nothing upstream of the controller knows what that particular machine will actually do when handed that particular feature.

And the reason is important, because it explains why two decades of excellent file format work never closed this gap. Identity, intent and context are all properties of the part. They can be written down, which is exactly why a standard can carry them. Behaviour is a property of the machine. It is not information about the part at all, so no file can hold it. It has to be computed, per machine, before the cut.

A part program is a sequence of coordinates and a commanded feedrate. It is not a statement of what will happen. The numerical control kernel interpolates that sequence into axial reference trajectories subject to drive limits, jerk and acceleration settings, smoothing configuration and the blending tolerance active at that moment. CAM models none of this. It integrates length over commanded feedrate and reports a number, and on real aerospace features the gap between that number and the machine is routinely measured in minutes rather than seconds.

So you can pass a feature-level tolerance from design to controller with perfect fidelity and still have no idea, at the point of programming, what it will cost or whether the machine can hold it. Continuity of identity, without continuity of physics. And a closed loop needs both, because measurement tells you what happened, and you cannot close a loop without knowing what should have happened. That is a forward model, and it has to run before the cut.

Using the richness already in the standard

We have been advocates of the benefits of STEP-NC for many years. Our CTO and I published research at HSM 2025 in Metz with Burak Sencer of Oregon State: Digital thread enabled time optimal trajectory generation for machining toolpaths.

It proposes no new standard. It uses the richness already sitting in the one we have. A STEP-NC polyline command is enriched with an explicit instruction to the interpolator, alongside the feature’s own geometric tolerance, straightness on an external profile, say, or cylindricity on a suitable three-dimensional feature. In other words, the contextual layer is used for what it was designed for: telling the machine not just where to go, but what kind of cut this is and how much room it has. Trajectory generation is then posed as a constrained optimisation in which every individual cutter line carries its own tolerance and its own objective. Position tolerance becomes a convex region around each nominal cutter line, rather than a single global setting buried in a cycle definition.

Benchmarked on-machine against a Hermle C52 with a Siemens 840D SL, the method delivered cycle time reductions of up to 14.4 per cent, with every trial landing within 0.1 per cent of the specified tool centre point tolerance.

To be clear about what that number is and is not: the 2014 demonstration’s 15 to 30 per cent came from human experts reworking a process once they could see it. This 14.4 per cent comes from the interpolation stage alone, on an unchanged process, using information the standard was already capable of carrying. The two are additive, not competing.

Tolerance is not a constraint on productivity. It is the lever. And because it can be set per cutter line, it can be spent where the drawing allows and held where it does not. On the same trochoidal path we also swapped the secondary objective between minimum time, minimum acceleration and minimum jerk, which is to say the same feature can be asked for the fastest cut, the smoothest cut or the lowest-energy cut, and the answer genuinely differs.

That is what altering specific points in a toolpath actually means once machine behaviour sits inside the model. Not a global smoothing slider. Feature-by-feature control, driven by the tolerance the designer specified, which is exactly the information a persistent identifier or an AP242 model already carries down the thread.

So, are we ready?

Twenty years of standards work has gone into getting the right information to the machine, and it worked. Identity, intent and context now travel the full length of the thread, which is more than anyone could say five years ago.

None of it tells you what will happen. A persistent identifier can carry precisely which tolerance applies to which feature, through every system in the chain, and still not tell you if the feature will pass or whether the machine standing on the floor can hold it. A common language lets the supply chain describe a feature exactly. It does not let anyone predict its conformance. Behaviour stops at the controller, because behaviour was never in the file.

The people who saw all of this in 2003 were not wrong. They were early, and they were short of several pieces. I think finally all the pieces are coming together. 

About the author. Dr Rob Ward is CEO and Co-Founder of DigitalCNC, a University of Sheffield AMRC spinout building deterministic, physics-based machining prediction inside CAM.

Sources and further reading

• Lockheed Martin, “Enabling a New Level of Precision in a Model-Based Enterprise”, July 2026
• Sandvik Coromant and the Dig4ReMan project, reported in Zerspanungstechnik.de, July 2026
• STEP Tools, “CAM Data Exchange on the Digital Thread using STEP-NC Demonstrated at IMTS 2014”
• S. Venkatesh, D. Odendahl, X. Xu, J. Michaloski, F. Proctor and T. Kramer, “Validating Portability of STEP-NC Tool Center Programming”, ASME IDETC/CIE, 2006
• M. Hardwick et al., “A Roadmap for STEP-NC-Enabled Interoperable Manufacturing”, International Journal of Advanced Manufacturing Technology 68, 2013
• D. Wilkinson, B. Sencer and R. Ward, “Digital thread enabled time optimal trajectory generation for machining toolpaths”, MM Science Journal, Special Issue HSM 2025, Metz, October 2025. DOI 10.17973/MMSJ.2025_11_2025140