How do you design a 3D printed spring that won’t snap?
Everyone’s first 3D printed spring is a coil, because that’s what a spring looks like. Print it standing up and it splits at the layers. Print it lying down and it isn’t really a coil anymore. The springs that work in FDM are flat: zigzags, rings, leaves and spirals, printed in the plane of the layers.
Applies to
- Process
- FDM / filament
- Features
- Button and switch return springs, latch springs, embedded dampers
- Orientation
- Printed flat, load in the XY plane
- Not for
- Coil springs; buy steel for those
Why it matters
A coil spring needs one continuous path of material wound through 3D space. FDM can’t give you that. Slant 3D says it plainly: the one spring they will never make is a coil spring.
Stand a coil upright and every turn is a stack of layers, so it splits along them under load. Lay it down and you get something coil-shaped that doesn’t behave like one.
So look at the coil from the top. That flat squiggle is your spring.
A flat extension spring is just a curved path going back and forth. Slant’s easiest method is a pattern of slots, with the ends rounded.
Round them. Square corners concentrate stress, and that’s where it cracks.
It won’t match a steel coil, mind you. A coil spreads the load evenly around every turn. A zigzag concentrates it at the bends, so when one fails it breaks right there, just below the curve.
Stiffness is the easy dial. Wider beams for stiffer. Thinner, down to about 1 mm, for softer. Or make the whole spring taller, so more material is bending and you get a lot more resistance.
And the big one. Slant calls it the most important thing with 3D printed springs: all the force has to be in plane, along the layer lines. Print a spring at an angle and you’ve ruined it. It has way less return.
Bonus: because flat springs print flat, you can print one inside a part as it grows. It’s captive the moment the print finishes, a return spring or dampener with no assembly step.
What good looks like
- A flat zigzag or slot pattern, not a helix
- Every bend rounded, no sharp inside corners
- Printed flat, with the load running along the layers
- No beam thinner than about 1 mm
- Comes all the way back after being stretched to working travel
How to apply it
- Decide the job: return force on a button or switch, give in a mount, or stored twist. The last two have their own pages (leaf springs and spiral springs).
- Draw the spring flat: a back-and-forth path, or a strip with rows of offset slots.
- Round every bend and every slot end.
- Set the beam width: wider for stiffer, down to about 1 mm for soft.
- Need more force in the same footprint? Make the spring taller in Z.
- Orient it so the spring lies flat and stretches in the XY plane. Never at an angle.
- If it lives inside the part, print it in place with a modeled gap around it, so it’s captive when the print ends.
Test it on your setup
- Print the spring on its own with a tab at each end.
- Stretch it to working travel a bunch of times and check it comes all the way back.
- Watch the bends. Whitening just below a curve means it’s overloaded: widen the beam or open up the bend.
- Change one thing per print, beam width or height, so you know which one did it.
Exceptions & tradeoffs
Mind you, plastic creeps. A printed spring held under constant load slowly takes a set and loses force. If the job is a long-life spring that’s always loaded, buy the steel spring and design a pocket for it.
Rings, leaves and spirals follow the same three rules: flat, in plane, rounded. They get their own pages because they do different jobs.
Common mistakes
- Printing a coil spring because that’s what springs look likeFlat zigzag or slot spring
- Square corners on the zigzagRound every bend
- Tilting the spring to fit it on the bedFlat, with the load in the layer plane
- Thinning the beam below 1 mm to soften itKeep ≥ 1 mm; lengthen the path or reduce the height instead
Frequently asked questions
- Can you 3D print a spring?Yes, but not a coil spring. FDM prints flat springs well: zigzag extension springs, leaf springs and spiral springs, all printed flat so the load runs along the layers.
- Why do 3D printed coil springs break?Printed upright, every turn of the coil is a stack of layer lines, and the load pulls them apart. Printed on its side it isn’t a true coil. A flat zigzag spring avoids both problems.
- How do you make a 3D printed spring stiffer?Widen the beams, or make the whole spring taller so more material bends. To make it softer, thin the beams down to about 1 mm or lengthen the path.
- What is the best orientation for a 3D printed spring?Flat, so the spring bends in the plane of the layers. Printed at an angle it loses most of its return.
No coil springs; flat extension spring from a coil’s top view; round the edges; wider is stiffer, down to 1 mm for softer; taller for more resistance — Learn 15 Print-in-Place Mechanisms in 15 Minutes ↗ at 05:53.
All spring force in plane along the layer lines; printing at an angle ruins the return — Learn 15 Print-in-Place Mechanisms in 15 Minutes ↗ at 09:42.
Flat springs can be printed inside a part as it’s made — Learn 15 Print-in-Place Mechanisms in 15 Minutes ↗ at 10:58.
The no-coil rule, the top-view trick, the 1 mm floor and the in-plane rule are all Slant 3D’s. The creep caveat is standard plastics behaviour. The test, the one-change-per-print habit and the mistakes are my editorial notes.