Clearance Guidelines

TL;DR

Pick a starting clearance based on the fit you need (free, sliding, locating, press), then print a small fit-test in the same orientation and settings; if it fuses you likely need more gap or less flow/temperature, and if it binds at the bottom edge fix elephant’s foot before changing the whole design.

What “clearance” means in FDM (and why it’s not one number)

Clearance is the intentional space between two mating features so they assemble and move without welding together. In FDM, the printed shape is influenced by bead width, corner bulge, cooling, and first-layer squish, so a modeled 0.20 mm gap may behave like 0.05 mm in one orientation and 0.30 mm in another. Sliding faces printed in XY can be smooth-ish; sliding faces formed by stacked layers in Z tend to feel stepped and can bind even when the dimensions are “correct.”

Fit variables that change your needed clearance

Orientation

XY features usually come out more consistent; Z-stacked faces can be stepped and higher friction.

Hole vs pin

Holes often print undersized; pins/bosses can print oversized from perimeter overlap and bulge.

First layer

Elephant’s foot reduces clearance near the build plate and causes “only the bottom binds.”

Material behavior

Shrink-prone or flexible filaments can tighten fits; filled filaments can add friction and wear.

Process state

Too much flow, too hot, poor cooling, or sloppy motion all make features effectively larger.

Post-processing

If you’ll drill/ream/sand/coat, design clearance to leave material for that step (don’t chase perfect off-printer sizes).

Starting clearance ranges (use as a first print, not a promise)

• Free-spinning / drops-in (pins, axles, hinges): start around 0.25–0.50 mm radial clearance (0.50–1.00 mm on diameter).
• General sliding fit (drawers, rails): start around 0.20–0.40 mm per side; increase if Z-stepping is on the sliding face.
• Locating fit (align but still removable): start around 0.10–0.25 mm per side; expect to tune hole/pin separately.
• Snap features (where you want engagement but not permanent): clearance is feature-specific; start with the sliding/locating guidance, then tune latch geometry and chamfers.
• Press fit (designed interference): start by calibrating extrusion/holes first; then add small interference (often 0.05–0.20 mm) and validate with a dedicated test coupon.

How to apply guidelines without guessing (a repeatable workflow)

1. Name the fit goal in the CAD: free, sliding, locating, snap, or press. Write down what “good” feels like (no wobble, no bind, removable by hand, etc.).
2. Pick one starting clearance from the ranges above (or your shop notes).
3. Print a fit-test that matches the real conditions: same orientation of mating faces, same wall count, same layer height, same filament, same cooling/speeds, same intended assembly direction.
4. If it’s too tight, diagnose before changing the model: check elephant’s foot at the bottom, check hole undersize vs pin oversize, and check flow/temperature for bulging.
5. Change only one variable per iteration: either adjust modeled clearance (preferred) or adjust a single print parameter (flow, temperature, horizontal expansion).
6. Record the winning value with context: printer, nozzle/line width, layer height, material, orientation, and whether it was hole-on-pin, slot-on-rail, etc. This becomes your personal clearance table.

Common failure patterns and the first fix to try