What’s the best way to join 3D printed parts?
Terrain tiles, an architecture model, a snap-together kit. Every one has a seam, and every seam either sits flush or jiggles. For joining 3D printed parts, Slant 3D ranks the usual joints and lands on one only printing can make: a lock-in tab that clicks into hidden recesses and pulls the seam tight.
Applies to
- Process
- FDM / filament
- Features
- Lock-in tabs, tongue and slot, T-slots, eye slots, grip fins
- Goal
- Parts that lock tight, flush and repeatably, with no supports
Why it matters
Most joints just slide together. Nothing pulls the two halves in, so the seam gaps and it wiggles.
Slant 3D walks the ladder. A plain tongue and slot is easy and weak. A T-slot holds sideways but brings a pile of tolerances and a warp-prone first layer. A spring T-slot finally pulls the seam tight. An eye slot is the easiest to tolerance. Grip fins add give.
Then he points out that almost all of those could be made another way. Molded, machined.
A lock-in tab can’t. The slot has two recesses inside it that no mold or cutter can reach. The tab’s two flanges flex, the bumps click into the recesses, and the seam pulls in. No jiggle, no fiddly XY tolerancing, no first-layer drama.
His verdict: if given the choice, use these. They use a smidgen less material, they’re more reliable, they’re easier to assemble, and they’re fairly easy to tolerance.
What good looks like
- The joint pulls the seam flush, no visible gap
- Flanges flex in and click into the recesses
- The flange undersides are angled so they print with no support
- Each part comes off the bed complete, with a simple first layer
- Click strength matches the job: reusable for a kit, permanent for a product
How to apply it
- Cut a slot into one part with two recesses inside it, one on each side.
- On the mating part, make two flanges that can flex, each with a lock bump that lines up with a recess.
- Angle the undersides of the flanges so they print without support.
- Orient the parts so each has a simple first layer. Slant 3D stands the brick up so the flanges print upright.
- Shape the bumps for the job. Rounded both ways for a kit you can pull apart. A hard catch for a permanent joint.
- Adjust the tolerance so the bumps pull the seam tighter.
- Where you still use a tongue, chamfer it so it wedges in.
Test it on your setup
- Print one pair, click it together and pull it apart ten times.
- A reusable joint should still click on the tenth go. A permanent one shouldn’t come apart at all.
- Run a fingernail over the seam. Flush means the tab is pulling.
Exceptions & tradeoffs
Mind you, the recesses live inside the slot, so this only works where the slot can be printed open and clean. Check the slice before you commit.
If a tongue has to print face-down on the bed, an eye slot is the kindest first layer (see Tongue and slot joints).
Where a lock tab won’t fit, a spring T-slot is the tongue-style joint that does pull tight (see Spring T-slots).
Common mistakes
- A plain square tongue with no chamferChamfer it so it wedges and the layer lines lock
- A short, stumpy slot that lets the top of the seam splay openUse a lock-in tab or spring T-slot that pulls the whole seam in
- Flat flange undersides that need supportAngle them so the part prints complete
Frequently asked questions
- What is the best way to join 3D printed parts?Slant 3D recommends lock-in tabs: flexing flanges with bumps that click into recesses inside a slot. They pull the seam tight, need no support, and are easier to tolerance than tongue joints.
- How do you connect 3D printed parts without glue or screws?Use a printed joint that locks: lock-in tabs, a spring T-slot, or grip fins around a round tongue. Each one flexes into place and holds the parts together on its own.
- Can 3D printed snap joints come apart again?Yes, if you want. Round the lock bumps both ways and the joint clicks apart, which suits building kits. Give the bumps a hard catch and it locks permanently.
- Why do my 3D printed parts wiggle at the seam?A plain tongue and slot has nothing pulling the halves together. Chamfer the tongue so it wedges, or switch to a joint that pulls in, like a lock-in tab or spring T-slot.
Why most joints can be made another way, and the print-only lock-in tab with internal recesses — Joining Features | Design for Mass Production 3D Printing ↗ at 06:18.
Reusable vs permanent lock bumps, supportless angled flanges, and simple first layers — Joining Features | Design for Mass Production 3D Printing ↗ at 07:31.
Recommending lock-in tabs over the other joints: less material, more reliable, easier to assemble — Joining Features | Design for Mass Production 3D Printing ↗ at 08:25.
The joint ranking and the lock-in tab design are Slant 3D’s, start to finish. The ten-click test and the fingernail check are ours. Each of his other joints has its own page here if a lock tab won’t fit your part.