Solidon3D turns a downloaded STL into a part that fits, without CAD
A desktop app that walks a model to a printable part along four routes, with a check report that runs before the slicer opens
Solidon3D, at solidon3d.de, is a desktop application built by Robert Schneider. It sets out to close the gap between a downloaded model and a part that actually fits, without first having to master CAD. The program leads to a printable part along four routes that all end in the same scene. The same operation history and the same check report lead to a separate decision for each part. The demo is already available, complete, and requires no account. It runs until 30 October 2026; after that date it stops launching, while the project files themselves remain untouched.
What happens when the demo expires
In practice this means that after 30 October 2026 the demo itself will stop launching, so the application will not open. Expiry does not, however, delete, lock or watermark existing work. That is a deliberate contrast with demos that, on expiry, take away or spoil what was made earlier.
Anything already exported to STL, 3MF, STEP, OBJ or PLY will open after the demo expires in any other program, without Solidon3D. Native projects, meaning the ZIP with JSON inside and the full editable operation history, do need a running Solidon3D to be reopened and edited further. The data itself does not spell out what happens to these files after 30 October: it says only that the demo stops launching and that projects remain untouched, so further editing of native files most likely requires the full version at that point, though the source does not confirm this outright.
Four routes to a printable part
The first route is editing someone else’s model. In a downloaded STL, holes, pockets and wall thicknesses are named features for the program, ones you can click and change by a number, and the file can be dragged straight from MakerWorld, Printables or Thingiverse, skipping the downloads folder. The second is building from scratch from dimensions and proven blocks such as nut seats, threaded inserts, threads or hinges; the agent sets up the parameters and embeds the blocks, and turning a number recalculates the model at once. The third is generating from text or an image. The fourth is sculpting shapes that cannot be dimensioned, with six brushes, where the whole session stays a single step in the history, and spots that are too thin show up as a number while you work.
The non-destructive history
What ties these four routes together is the non-destructive history. Every step remains an operation that can be changed at any moment, and changing one dimension recalculates the model even 20 steps later. Taking a wall from 2.40 to 3.60 millimetres pulls the hollowing, the lid, the holes and the fits through the recalculation with it. The register holds 86 such operations, 40 standard part sizes and 16 printer profiles, plus 9 ready example projects.
What the program shows before the slicer
The core is what the program shows before the slicer starts. The check report flags open edges, reversed normals, walls thinner than two extrusion widths and a file that did not state its unit, and it counts findings by errors, warnings and notes; each one jumps to its place in the model and carries a suggested action. Layer analysis shows overhangs, islands, bridge lengths and support volume without firing up the slicer, and the orientation search suggests the pose that leaves the fewest of them. Fits come from the material profile: clearance, interference and flush fit come off a calibration ladder that you print once, instead of guessing on the third attempt. When a part is too large for the bed, a single operation splits it and adds its own pins, holes and fits.
The optional AI layer
The AI sits on top and is optional. Instead of clicking through menus, you can describe in the chat what should happen, and the agent reaches for the same tools as the menus, with its proposal undone by a single undo. Geometry is computed by code throughout, while the language model stays with turning a sentence into an operation; the creator measures this, running 39 reference requests against every agent change. The chat runs on the user’s own API key, where the provider charges pennies per proposal, or locally through Ollama for free, which needs a model on the order of 14 billion parameters and a graphics card with 16 GB of memory. Without AI, without an account and without internet, the rest of the program works in full.
What Solidon3D does not do
Solidon3D is not a slicer: it analyses and prepares the part, while the print file comes out of the slicer, to which the program hands the model and whose G-code it reads back as a cross-check. It keeps projects as files on disk, a zipped archive with JSON inside, with export to STL, 3MF, STEP, OBJ and PLY, so there is no cloud and no telemetry here. The generative route calls for the most caution. A mesh from text or an image goes through a repair chain and comes out printable in some 20 seconds, but the program itself states that it gives no dimensional guarantees for generated meshes, and precise design stays on the first two routes. This also needs a local ComfyUI with a generator model and a strong card; without them, editing and building from dimensions remain.
Demo, distribution and price
The demo is the full version with a single end date: no watermarks, no export lock, no features held back for later. The Windows 10/11 package weighs 179 MB, the Linux Flatpak version 260 MB, and macOS comes in two packages; on first launch Windows shows a blue notice about an unsigned application, because the signature will follow once the certificate is in. The licence is tied to a person rather than to a single computer, so it covers the desk, the laptop and the machine in the workshop, and commercial use is included. The full version costs 69 EUR one time, with every update from the 1.x branch included in the price. After 31 January 2027 the price rises to 99 EUR.
