LEARN · 2026-10-06
3D-printed hole tolerances: why holes shrink and how much clearance to add
Why FDM, SLA and SLS holes come out undersized, recommended compensation per process, press / slide / loose fit clearances and tips for captive nuts, bearings and pins.
Why do holes shrink?
Slicers turn circles into polygons, extruded lines bulge inward at corners and cooling shrinks inner contours; horizontal holes also sag at the top. Small FDM holes often come out 0.1–0.3 mm undersize. SLA over-cures slightly, and SLS powder can clog small holes.
Recommended compensation
| Process | Vertical hole | Horizontal hole | Smallest reliable hole |
|---|---|---|---|
| FDM 0.4 mm nozzle | +0.2 mm | +0.3 mm (or teardrop) | 2 mm |
| SLA / DLP | +0.1 mm | +0.1 mm | 0.5 mm |
| SLS / MJF | +0.15 mm | +0.15 mm | 1 mm (must depowder) |
TIPPrint a hole test plate (e.g. 2.8–3.4 mm in 0.1 mm steps) to find what your machine really needs.
Shaft / hole clearances
| Fit | Diametral clearance (FDM) | Use |
|---|---|---|
| Press | −0.05 to 0 mm | Bearings, magnets, dowels |
| Transition | 0 to +0.1 mm | Removable locating |
| Slide | +0.2 to +0.3 mm | Shafts, sliders |
| Loose | ≥ +0.4 mm | Print-in-place hinges |
For precise fits start from ISO 286 (H7/g6, H7/k6 …) and add the process compensation — the ISO fit calculator gives the deviations for any size.
Captive nuts and bearings
- Hex nut pocket: across-flats + 0.2–0.3 mm, depth + 0.2 mm.
- Bearing seat: OD + 0.1 mm press fit, or + 0.2 mm and glue.
- Heat-set inserts: follow the vendor hole size, usually 0.3–0.5 mm under the insert OD.
FAQ
Compensate in CAD or in the slicer?
In CAD (or the Library's bore-clearance field) — slicer XY compensation changes the whole outline.
Horizontal holes sag at the top.
Use a 45° teardrop top or a removable sacrificial bridge layer.
Do I compensate when ordering from a print service?
Professional SLS / MJF / SLA machines are calibrated, but mark critical fits with tolerances — Orinovate will confirm them when quoting.