A GitHub repository called robertsamples/INDX-CAD now hosts something Prusa never shipped: parametric CAD for the INDX toolhead, complete with internal geometry, reconstructed from the printable mesh Prusa itself released. The repo's description is blunt about the method — "reverse engineered CAD from Prusa's printable model with internal geometry" — and the contents match. Alongside a README and a license file sit INDX.f3z (a Fusion 360 archive), INDX.step (the vendor-neutral solid model), and indx_toolhead_8t.3mf, the original Prusa mesh, kept, in the author's words, "for archival purposes." Twenty-two commits on main. No press release, no announcement post.

That last part is deliberate. The author states the model was originally uploaded to Printables but that the original and its remixes were removed, which is why the reconstruction now lives "in a less visible space than usual 3DP hosting sites."

The mesh-to-CAD problem, and why this one worked

Converting a triangle mesh back into editable solid geometry sounds mechanical and isn't. An STL or 3MF describes a surface as a soup of facets; it carries no notion of a cylinder, a fillet radius, a sketch plane, or a feature tree. Reconstruction tools infer those primitives — fit a plane here, detect a cylindrical patch there — and output quality depends almost entirely on how faithfully the source mesh represents the shapes underneath.

The repo's own caveats make that dependency legible. The author asks readers to "consider this a work in progress," and the failure mode is telling: filleted components, mostly injection-molded parts, "did not convert as well as CNCed parts." A machined face is a plane or swept arc with hard boundaries — a solver locks onto it. A molded part is a continuum of draft angles and variable-radius blends that tessellate into hundreds of nearly-coplanar triangles with no crisp edges to key off.

The other half of the story is the source material. Getting to a STEP file with recoverable internal geometry means Prusa's printable was clean: sensibly tessellated and honest about the part rather than a decimated approximation. Vendors often ship meshes simplified for print convenience, and those reverse-engineer into mush. This one didn't.

Where the licenses collide

The repository is licensed CC BY-SA 4.0, and the author's stated basis is that Prusa's printable was itself CC BY-SA 4.0 — a share-alike license, so a share-alike derivative is the compliant outcome.

The complication is Prusa's Open Community License, updated to v1.1 on June 24, 2026 — the license under which Prusa released the CORE One, CORE One L and CORE One+ printer CAD, plus the INDX upgrade's printable parts for the CORE One+, hosted on Printables and GitHub. OCL v1.1 is permissive in ways that matter to working shops: internal business use including production, repair, prototyping, optimization and training; private modification with no obligation to share; compatible accessories that attach without becoming derivatives; and the right to use OCL-licensed tools to manufacture your own products.

What it does not permit is the thing this repository does. OCL v1.1 forbids distributing derivatives under any non-OCL license: distribute a derivative and you distribute it under OCL. Its optional plugins add further conditions on top of that base: the Micro Business plugin sets a €1,000,000 annual gross revenue threshold over a rolling twelve-month window, above which a business needs a separate licensing agreement, and the Research and Development plugin narrows business use to R&D, with manufacturing requiring an agreement of its own. Prusa's derivative test is unusually clear: "designing an accessory that attaches to a CORE One doesn't make it a derivative," because a derivative arises when the original licensed geometry ends up inside yours. Reconstructed CAD of an INDX toolhead is not an accessory that bolts on. It is the geometry.

So the two accounts cannot both be right about the same file. Either the 3MF the author pulled carried CC BY-SA 4.0 when it was downloaded, in which case share-alike attaches and OCL is beside the point for that artifact — or the INDX printable parts were OCL from the outset, in which case a CC BY-SA 4.0 re-release is precisely the distribution OCL prohibits. Archiving the original 3MF inside the repo reads as an attempt to preserve the evidence. The removal from Printables reads as the reason the question got asked.

The "open" part is the fight

None of this would be sharp if OCL were an ordinary open license. Critics argue it isn't. Adafruit published a lawyer's line-by-line critique of OCL v1 on March 19, 2026, arguing that the Open Community License is neither open nor for the community — that it functions as a non-commercial license dressed in open-source clothing, and is not open source by any definition that matters, whether the OSI's, the Open Source Definition, or OSHWA's.

That critique is why a CC BY-SA 4.0 fork of INDX is contentious rather than routine. CC BY-SA is a known quantity with a long track record; OCL is a bespoke instrument with revenue thresholds and a plugin system layered on top. A community that spent years treating "released the CAD" as synonymous with "you can fork it" is discovering the phrase carries a vendor-specific asterisk, and reverse-engineering is the pressure test that surfaces it.

What It Means for Makers

Practically, three things. First: if you download vendor CAD or printable parts, capture the license as it appeared on the page you pulled it from. Terms get revised, models get pulled, and "it said CC BY-SA when I got it" is only an argument if you can show it. The archival 3MF in this repo is that instinct expressed as a commit.

Second: OCL's permissions are broad for use and narrow for redistribution. Repairing your machine, modifying it privately, printing spares, running it as production equipment, and designing attach-on accessories are all explicitly fine under v1.1. Publishing a modified toolhead under a license of your own choosing is the line, and it is the one INDX-CAD stands on.

Third, and this should concern Prusa more than any single repository does: the venue shift matters. When a reconstruction lands not on Printables but in what its author calls a less visible space, the vendor loses visibility into what people build on its hardware, and the community loses the review and remixing a mainstream host provides. INDX-CAD is a work in progress with imperfect fillets and an unresolved licensing basis. It is also proof that a clean printable mesh is a CAD distribution channel whether the vendor intends it or not — and that where such forks can legally live is unsettled enough that people have started hedging by hosting quietly.

Sources