3D printing tolerance test
Generate a fit test coupon — a row of holes stepping through a clearance range, plus one gauge pin to try in them
How much slack a printed joint needs is a property of your printer, filament and slicer rather than of the design — so this replaces the usual print-it-twice with one plate: a row of holes or slots stepping through a clearance range, each station engraved with its value, plus a gauge pin at the nominal size. The first station the gauge enters cleanly is your real clearance. Run it once round and once flat; they differ. Download a print-ready STL or 3MF.
How the 3D printing tolerance test works
What you can adjust
- Feature — Pin & hole · Tab & slot
- Nominal size — 1–100 mm
- Stations — 2–12
- First clearance — 0–2 mm
- Clearance step — 0.01–1 mm
- Plate thickness — 1–20 mm
- Engrave the clearances
3D printing tolerances: Tight, Normal and Loose
Every part that has to mate with another carries a Fit control. Clearance is always stated as a total: the whole difference between the hole and the part, half of it on each side.
| Fit | Clearance | Use it for |
|---|---|---|
| Tight | Normal − 0.15 mm | Parts that must not rattle: press-in pins, lids that have to stay put. |
| Normal | Each generator’s own tested clearance | The default. Snap-fits, hinges and ball joints each have their own. |
| Loose | Normal + 0.15 mm | Parts that must move freely, or that bind on your printer. |
| Custom | The number your coupon reads | Every joint built to your printer instead of to an average one. |
The default coupon’s clearance ladder
Each station is cut at the pin’s size plus its clearance, so the clearance is the whole difference across. With the default 6 mm pin:
| Station | Clearance | Hole | Per side |
|---|---|---|---|
| Station 1 | 0.05 mm | 6.05 mm | 0.025 mm |
| Station 2 | 0.1 mm | 6.1 mm | 0.05 mm |
| Station 3 | 0.15 mm | 6.15 mm | 0.075 mm |
| Station 4 | 0.2 mm | 6.2 mm | 0.1 mm |
| Station 5 | 0.25 mm | 6.25 mm | 0.125 mm |
| Station 6 | 0.3 mm | 6.3 mm | 0.15 mm |
Measuring your printer’s real tolerance
- Print it the way you print parts. Same filament, same layer height, same profile. Clearance is a property of your printer, filament and slicer, not of the design.
- Work along the row from the tight end. Try the pin station by station. The first one it enters cleanly is your printer’s real clearance for that fit. Each station has its value engraved below it.
- Measure a hole and a slot. Switch Feature between Pin & hole and Tab & slot. A round bore and a flat slot do not come out the same, because the seam and the perimeter order land differently. Keep both numbers.
- Use the number. On the snap-fit, annular snap, pin hinge or ball joint, set Fit to Custom and type in what you read.
- Parts printed assembled need more. Hinges, bearings and ball joints come off the plate already assembled. Two surfaces printed in the same pass closer than about 0.15 mm can weld together, so those generators hold a Custom clearance at or above it.
Tolerance questions
What tolerance should I use for 3D printed parts?
There is no single number: it depends on your printer, filament and slicer. Start with Normal, print the coupon (its ladder runs from 0.05 mm to 0.3 mm), and use the value of the first station the pin enters.
How do I test my 3D printer’s tolerance?
Print the coupon and its pin with your usual settings, work along the row from the tight end, and note the first station the pin enters cleanly. That is your number.
Is clearance per side or total?
Total. The hole is the pin plus the clearance, so 0.2 mm of clearance is 0.1 mm on each side. Every Fit control in OwlCAD uses the same convention.
Why do a hole and a slot give different numbers?
The seam and the perimeter order land differently on a curve than on a flat face, and almost every printer comes out looser on one of the two. Measure both.