How to 3D print hinges: pin size and clearance for each hinge type

There are four ways to 3D print a hinge, and each turns on one number. A pin-and-knuckle hinge needs a bore 0.40 mm larger than its pin (2.15 mm for a 1.75 mm filament pin), and a print-in-place hinge 0.30 to 0.40 mm per side. A snap-on clip’s mouth is about 2% narrower than its pin in PLA (polylactic acid), and a living hinge is a web 0.4 to 0.6 mm thick.

What pin size and clearance does a 3D printed hinge need?

A 3D printed hinge assembled after printing needs a bore 0.30 to 0.50 mm larger than its pin (0.15 to 0.25 mm per side). At 0.20 mm per side, a 1.75 mm filament pin takes a 2.15 mm bore and an M3 screw a 3.4 mm hole. A print-in-place hinge needs 0.30 to 0.40 mm per side.

Per side is the gap at one face. Total is the bore minus the pin. The ranges are QIDI’s for a 0.4 mm nozzle, 0.2 mm layers and PLA or PETG (glycol-modified polyethylene terephthalate). The defaults come from the tolerance calculator.

Hinge type	Clearance per side	Total, on the diameter	Use it for
Pin and knuckles, assembled after printing	0.15 to 0.25 mm (default 0.20)	0.30 to 0.50 mm	Lids and doors that carry load or come apart
Pin ends pressed into the outer knuckles	-0.05 mm (interference)	-0.10 mm	Keeping the pin from sliding out
Print-in-place	0.30 to 0.40 mm (default 0.35)	0.60 to 0.80 mm	One-piece boxes and toys, no hardware
Snap-on clip over a pin	0.20 mm running, plus a mouth narrower than the pin	0.40 mm	Lids that unclip
Living hinge	none: a 0.4 to 0.6 mm web	none	Flip-top caps in nylon or TPU

QIDI adds 0.05 to 0.10 mm per side for ABS (acrylonitrile butadiene styrene) and ASA (acrylonitrile styrene acrylate), and 0.10 to 0.20 mm for unfilled nylon.

How to make 3D printed hinges with a separate pin

A pin-and-knuckle hinge is two leaves whose knuckles interleave, with one pin through all of them. Snapmaker names three pins: a length of raw filament, a metal screw, or a printed pin. The pin turns in clearance through most knuckles and grips in the outer ones.

Pin	Pin diameter	Bore it turns in (0.20 mm per side)	Range (0.15 to 0.25 mm per side)	Press-fit end hole (0.05 mm per side interference)
1.75 mm filament	1.75 mm	2.15 mm	2.05 to 2.25 mm	1.65 mm
3 mm steel dowel	3.00 mm	3.40 mm	3.30 to 3.50 mm	2.90 mm
1/8 in steel rod	3.175 mm (0.125 in)	3.58 mm (0.141 in)	3.48 to 3.68 mm	3.08 mm (0.121 in)
5 mm steel dowel	5.00 mm	5.40 mm	5.30 to 5.50 mm	4.90 mm
M3 screw	3 mm	3.4 mm (ISO 273 medium)	3.2 mm (fine) to 3.6 mm (coarse)	none: hold it with a nut

• Filament pins: Prusa Polymers makes Prusament PLA and PETG to 1.75 ± 0.02 mm, so the 0.40 mm of total clearance covers the spool’s variation. Filament is one continuous extrusion, so it has no layer lines to shear along.
• M3 screw: the ISO 273 medium-series clearance hole is 3.4 mm, which leaves 0.20 mm per side, the same as the turning-pin default. The fine series, 3.2 mm, leaves 0.10 mm per side for less play. The screw hole size calculator has the other screw sizes.
• Holes print small: these are the sizes the printed bore should measure. QIDI notes internal holes come out undersized, with about four times the error of outside dimensions. Measure a printed test hole, then add the shortfall to the model or use the hole compensation calculator.

How do you keep a press fit hinge pin from sliding out?

Make the hole in one or both outer knuckles 0.10 mm smaller than the pin. That is 0.05 mm of interference per side, and the pin grips there while it turns freely in the middle knuckles. For a 1.75 mm filament pin the hole is 1.65 mm.

QIDI publishes 0.05 to 0.15 mm of interference per side for a press-fit pin. It warns that past about 0.20 mm the boss “splits along a layer line instead of gripping.” Start at the light end, because a hole that prints 0.10 mm small already adds another 0.05 mm per side.

Use an odd number of knuckles. Both outer knuckles then belong to the same leaf, so the pressed pin is fixed to that leaf and turns in the other leaf’s knuckles.

Knuckle gaps and wall thickness

• Gap between knuckles: leave 0.20 to 0.30 mm between neighboring knuckle faces, QIDI’s clearance for faces that slide on each other. The tolerance calculator’s sliding default is 0.25 mm.
• Wall around the bore: Sovol’s fix for small hinge pins that shear along their layers is 3 or 4 perimeter walls, so the part is built from continuous perimeters rather than infill. Give the knuckle at least three perimeters around the bore, which Prusa’s table puts at 1.35 mm on a 0.4 mm nozzle (0.45 mm per perimeter). Set 3 or 4 walls in the slicer.
• Knuckle diameter: bore plus twice the wall. At 1.35 mm walls that is 4.85 mm around a 2.15 mm filament-pin bore and 6.10 mm around a 3 mm dowel’s 3.40 mm bore.

Worked example: a box lid hinge on a 1.75 mm filament pin

1. Split the hinge into five knuckles: 1, 3 and 5 on the box, 2 and 4 on the lid.
2. Model a 1.65 mm press-fit hole in knuckles 1 and 5, and a 2.15 mm bore in knuckles 2, 3 and 4.
3. Make every knuckle 5.0 mm across, which leaves a 1.43 mm wall around the 2.15 mm bore.
4. Leave 0.25 mm between neighboring knuckles.
5. Print both parts with the leaves flat on the bed. Draw the bores as 45° teardrops so their tops bridge, or print them undersized and drill them with a 2.2 mm bit, which leaves 0.225 mm per side.
6. Push the filament through knuckle 1 until it seats in knuckle 5, then trim it flush.

Print-in-place hinge clearance

Model 0.30 to 0.40 mm per side between a print-in-place hinge’s pin and barrel (0.60 to 0.80 mm on the diameter). The hinge comes off the bed assembled, so that gap is all that stops the pin fusing to its barrel. QIDI sets the range, roughly twice a hand-assembled joint’s, because the gap must exceed about one extrusion width or the walls weld. Sovol starts lower in PLA, at 0.25 mm per side, and adds 0.05 to 0.10 mm for PETG.

Gaps that run in Z must be whole layers: 0.4 mm at 0.2 mm layers (QIDI), and Stratasys asks for at least twice the layer height. Where the top of the barrel bridges over the pin, QIDI adds 0.10 mm, since the first layer over air sags 0.05 to 0.15 mm. The print-in-place clearance guide covers chains, ball joints and gears.

How to design a 3D print snap fit hinge or pivot

A snap-on hinge is a C-shaped clip on one part that snaps over a pin on the other part and pivots on the pin. Size the C’s bore as a turning fit, then make its mouth narrower than the pin by the undercut the plastic can stretch through:

bore   = pin + 0.40 mm                  (0.20 mm per side, turning)
mouth  = pin - ε × bore

ε      = 0.70 × the filament's yield strain   (snapped on once)
       = 0.60 × that                          (unclipped often)

For a 6 mm pin and a 6.40 mm bore:

Material	Printed yield strain	ε	Undercut	Mouth	Mouth, unclipped often
PLA	2.9% (Prusament PLA)	2.0%	0.13 mm	5.87 mm	5.92 mm
PETG	5.1% (Prusament PETG)	3.6%	0.23 mm	5.77 mm	5.86 mm

The formula is the annular snap-joint rule from Bayer’s Snap-Fit Joints for Plastics guide, now Covestro’s. A ring forced over a bead may stretch by strain times diameter. Amorphous plastics may take about 70% of their yield strain for one brief snap, and joints taken apart often get 60% of that.

A closed ring is the strict case. The guide sizes a ring with slits as cantilever arms, because the arms bend instead of stretching. A C-clip with a thin back can therefore take a deeper undercut than the table gives. On a small pin the ring figure is tiny: 0.13 mm in PLA is 0.065 mm per side, inside the ±0.15 mm QIDI budgets for features under 10 mm.

Print a test clip and deepen the undercut in 0.05 mm steps until it holds. Lay the C flat on the bed so it bends along its layers, QIDI’s rule for snap hooks. QIDI also says PETG survives snap cycles that would crack PLA “on the third open.” It keeps PLA to snaps assembled once.

Living hinges

Print a living hinge as a web 0.4 to 0.6 mm thick with at least two layers, the figure Protolabs Network gives for FDM (fused deposition modeling) printing, with no pin and no clearance. QIDI allows up to 0.8 mm. Its material is nylon 12, or TPU (thermoplastic polyurethane) on a dual-extrusion printer. Molded living hinges are almost all polypropylene or polyethylene.

Orient the part so the hinge’s width builds up one layer at a time, and each layer crosses the hinge in a single strand. Expect a short life: the FDM test hinge Protolabs Network shows lasted 25 cycles. The living hinge guide covers the web’s shape.

Should you print a hinge flat or standing up?

Print a hinge flat when it carries load, and standing up when a round, smooth bore matters more. Printed flat with the pin axis along the bed, its layers run the length of the hinge and resist the load, but the bore prints slightly oval. Standing up, the bore is round, but the knuckles’ layers peel apart under load.

• Flat (pin axis horizontal): QIDI’s hinge repair guide says flat gives maximum strength against a door’s weight, and corrects the oval bore with XY size compensation or in CAD. Snapmaker also says to lay hinges flat. Sovol suggests a 45° teardrop bore so the top bridges, and Protolabs Network says overhangs up to 45° usually print without support.
• Standing up (pin axis vertical): QIDI says this gives the best circularity, but the knuckles “are now prone to snapping off” because opening the hinge peels the layers apart. Sovol prefers vertical pins for print-in-place joints for the same round bore, and Stratasys calls the X/Y plane the most accurate one for mating surfaces.
• The pin itself: Sovol warns that small printed pins standing up can shear along their layers. Use 3 or 4 walls, or swap in filament or a steel dowel.

Why does a printed hinge bind, wobble or crack?

• Binds only at the bottom knuckle: that is elephant’s foot, the first layers squashed wider. Chamfer the bottom edges 0.4 mm × 45° and set elephant-foot compensation to 0.15 to 0.25 mm (both QIDI).
• Binds along its whole length: the bores printed small. Measure one, then add the shortfall in the model or with the hole compensation calculator. Protolabs Network’s alternative is to print the hole undersized and drill it to size. For print-in-place parts, Snapmaker says lowering flow by 2 to 5% “is often enough” to free them, and Sovol adds 0.05 mm per side to the gap.
• Print-in-place hinge fused solid: QIDI says flexing it once firmly can free it, though the surfaces stay rough. Reprint with the Z gap at a whole number of layers.
• Wobbles: drop to the snug fit, 0.10 mm per side. QIDI’s repair guide models the hole for an 8 mm pivot pin at 8.15 to 8.2 mm for a fit with no wobble. Tighten in 0.05 mm steps (QIDI) rather than going straight to zero.
• Knuckle cracks: print flat, raise the wall count to 3 or 4, and thicken the knuckle. If it splits at a press-fit end, the interference is too high: measure the printed hole and keep it under QIDI’s 0.20 mm limit.
• Snap-on clip cracks: use the “unclipped often” mouth, or print the clip in PETG.