What is Fitment Co-Pilot?

Fitment Co-Pilot is a SliceFoundry generation mode that injects FDM clearance intent — press, locating, sliding, or loose — for holes, shafts, bearing seats, lids, and other mates so printable STLs prioritize assembly fit over visuals alone.

What clearance should I use for a 3D printed M4 hole?

For FDM (PLA/PETG), start around 0.15 mm per side for a locating / transition fit, then tune for your printer. Fitment Co-Pilot applies that class to declared fastener holes so you are not stuck at raw nominal diameter.

Can AI generate parts with press fits and bearing seats?

Yes. In SliceFoundry, enable Fitment Co-Pilot, choose press or locating (for seats) or sliding/loose (for slip), declare a bearing seat or shaft/bore mate, and generate. Refine after a test print if your machine runs systematically oversized or undersized.

3D Print Fitment Generator — Clearance-Aware Models That Actually Assemble

Most AI 3D generators optimize for looking right in a render. Functional makers need the opposite: mates that assemble on an FDM printer — bolt clearance holes that aren't too tight, bearing seats that press or slip as intended, lids that seat without grinding, and shafts that spin instead of seize.

SliceFoundry's Fitment Co-Pilot is built for that audience. In the model generator you declare fit intent (auto-detect, specify mates, or leave fit to the description), choose a fit class, and optionally name critical mates. The pipeline injects FDM-safe per-side clearances into the generation plan so dimensional discipline beats cosmetic guessing.

Who This Is For

Repair & replacement-part printers — knobs, clips, covers, and adapters that must mate to existing hardware.
Enclosure builders — project boxes, lids, PCB standoffs, and port cutouts with intentional gaps.
Mechanical makers — brackets, jigs, bearing housings, axles, and D-shaft fits.
Anyone burned by dimensional drift — models that preview fine but fail the caliper test after printing.

Fit Classes (Per-Side Clearance Starting Points)

Clearances below are typical per mating face (radial for bores/shafts), tuned for PLA/PETG around ~0.2 mm layer height — starting points, not ISO hard standards. Override when you know your printer's bias.

Press (~0.05 mm) — near-interference; almost no play.
Locating (~0.15 mm) — firm assemble, still removable (great default).
Sliding (~0.30 mm) — running / close lid and shaft motion.
Loose (~0.50 mm) — easy drop-in and oversized hardware clearance.

Mate Types You Can Declare

Fastener hole — M3/M4/M5 clearance or tap pilots.
Shaft / bore — pins, axles, D-shafts.
Bearing seat — e.g. 608 OD seats (press or slip).
Enclosure / lid — box–lid stack clearance and rabbets.
Snap / clip — living hinges and clip deflection gaps.
Custom mate — any other critical contact face.

How Fitment Co-Pilot Works

Open the 3D model generator and describe the functional part (dimensions help).
Set Fit & clearance — Auto-detect, Specify mates, or Off (description-only).
Pick a fit class and optional nominal size / clearance override.
Generate, preview, and refine — iterate with follow-ups if a mate still needs tuning.
Download the STL and slice in Orca, Cura, PrusaSlicer, Bambu Studio, or Flash Studio.

Example Prompt (with Fitment enabled)

"Electronics project box 100 × 70 × 40 mm outside, 2.5 mm walls, snap-fit lid on an inner ledge, four M3 mounting holes in the base corners 8 mm from each wall, and two 8 mm cable holes on one short face."

Then set Fitment to Specify: Enclosure/lid + Fastener hole, fit class Locating (or Sliding for the lid if you want freer motion).

Why Fit-Critical Generation Matters

FDM shrinks and squashes holes. Nominal Ø on screen is not printed Ø — intentional clearance saves failed reprints.
Silhouette AI lies about mates. A pretty bearing boss that measures 0.4 mm tight is scrap.
Named critical dims travel with the model. Params stay tunable for press vs slip without reinventing the part.
Same tool for first-time makers and skilled printers. Auto-detect for speed; Specify when you know the hardware.

Related Generators

After generating your model, export the STL and open it in Cura, OrcaSlicer, Flash Studio, PrusaSlicer, or Bambu Studio. Refine the geometry with follow-up prompts until the fit is exactly right — no CAD required.

Generate a Fit-Aware Model

Open SliceFoundry and generate with Fitment Co-Pilot →

Prefer Hands-On CAD? Try Draftr

When you'd rather design a part precisely by hand than generate it from a prompt, Draftr is a desktop CAD application for Windows and macOS that combines AI with organic parametric CAD in an IDE-like workspace. It pairs a full parametric toolset — sketches, pads, pockets, fillets, chamfers, patterns, and threads — with natural-language AI commands, then exports print-ready STL files. It's the natural next step once you outgrow prompt-based generation and want precise, editable, parametric models. Learn more at draftrcad.com.