Enter the two shaft sizes — 5 mm motor to 8 mm lead screw by default — and get a rigid coupler with a split clamp or set screws, nuts held in printed traps. Rigid on purpose: on a 3D printer's Z axis a flexible coupler can show up as banding, and printed helical beams are too weak to be worth it.
The real generator runs in your browser: set the parameters, then download STEP or STL. Nothing to install, no sign-up.
The first open downloads the CAD engine (about 20 MB).
Each parameter below rebuilds real geometry on every change — this is parametric CAD, not a scaled mesh.
| Parameter | Default | Range | What it does |
|---|---|---|---|
| Bore 1 (motor)BORE_1 | 5 mm | 3 – 14 | 5 for a NEMA 17 motor. |
| Bore 2 (lead screw)BORE_2 | 8 mm | 3 – 14 | 8 for a T8 lead screw. |
| Bore clearanceCLEARANCE | 0.3 mm | 0 – 0.6 | Added to both bores: printed holes come out small. |
| FasteningFASTENING | clamp | clamp / set-screws | Clamp: a slit and one screw per shaft. Set screws: two per shaft, 90° apart. |
| LengthLENGTH | 25 mm | 20 – 40 | Each shaft goes in half the length. |
| ScrewSCREW | M3 | M2.5 / M3 / M4 | With a nut in a hex trap; the body grows past 20 mm when bore and screw need it. |
Every parameter can go in the page's link, so one link opens exactly the part you want. Example (6.35 mm (1/4") to 8 mm, clamp):https://www.forgent3d.com/en/generators/shaft-coupling-generator?BORE_1=6.35&BORE_2=8
STEP AP214 in millimetres, exact B-rep — it opens directly in SolidWorks, Fusion, FreeCAD, Onshape or Inventor, and goes straight into a CNC quote form. STL for the slicer is one click too.
| This generator | Typical online STL generator | Vendor CAD library | |
|---|---|---|---|
| Any size within the range | Yes | Yes | Catalog sizes only |
| STEP with exact surfaces | Yes | Usually an STL mesh only | Yes |
| Changes the sliders don't cover | “AI edit” on the page | No | No |
| Account needed to download | No | Usually no | Often |
Every parameter is a link parameter; the link below opens the example part. ChatGPT, Claude or any assistant can write one like it from the parameter list (names, units, ranges) at: parameter list (JSON)
Example: https://www.forgent3d.com/en/generators/shaft-coupling-generator?BORE_1=6.35&BORE_2=8
Press “AI edit” in the generator and say what to change — a keyway, holes, a different shape. The AI edits the part's model.py and it rebuilds in your browser, with undo. A few edits a day are free without signing in; to keep the result or go further, copy it into your models and continue with the AI agent.
Edit with AI →For bigger changes, several rounds, or a part you want to keep: copy it into your models (free account). The Forgent3D AI agent reads the model.py, edits it, rebuilds it and checks the result itself.
Copy and continue with the AI agent →Rigid for a 3D printer's Z axis: Ooznest notes that a flexible coupler there can reduce print quality, and spiral couplers are not meant to carry the axial load. Flexible couplers make up for misalignment on machines that need it — a printed rigid one does not.
Start at the default +0.3 mm (5.3 for a 5 mm shaft): makers use +0.25–0.4 on small printed holes, PETG a little more than PLA. Too loose and it slips, too tight and it splits.
Standing up, so the bores print as round vertical holes; 4 perimeters, at least 35 % infill, PETG. No supports needed.
https://www.forgent3d.com/en/generators/shaft-coupling-generator?BORE_1=5&BORE_2=8 is exactly that: a rigid 20 × 25 mm clamp coupler with an M3 screw and nut per shaft. Print it standing up in PETG, 4 perimeters, at least 35 % infill.
Print it in PETG rather than PLA (a warm stepper shaft softens PLA at 50–60 °C, PETG at 70–80 °C), use the clamp rather than set screws — or set screws 90° apart: https://www.forgent3d.com/en/generators/shaft-coupling-generator?FASTENING=set-screws — and lower CLEARANCE if the bore is loose. For a D-shaped motor shaft, press “AI edit” and give it your shaft's flat.
Yes. Models you generate and the STL / STEP files you export are yours: print them, sell the prints, or use them in a product. No attribution to Forgent3D is required.
Already have your own .scad file? Convert OpenSCAD to STEP → · Preview it in the browser →
