Print-in-Place Hinges and Joints

What makes print-in-place work

A print-in-place hinge, chain or articulated figure is printed already assembled. It works only if the moving pieces never touch while printing: each is its own closed shell, separated from its neighbors by a gap the printer can keep open. Three things close that gap: too small a clearance, a first layer that spreads, and support material inside it.

Make the parts truly separate

• Separate shells. Each moving piece must be its own closed mesh. If you join everything with a Boolean union in CAD, the joint becomes one solid.
• No overlaps. The 3MF specification says that where items overlap, the printer software must unite them. A pin that overlaps its socket by even a little prints welded in place.
• Check the count. Blender's 3D Print Toolbox has a Shells check (Blender 4.3 or newer) that counts mesh islands. A three-part hinge should report three. If it reports one, the parts are joined somewhere.

Each shell also has to be manifold on its own; see Meshes, Manifolds and Normals.

Clearance: start at 0.3 mm, then test

Prusa's modeling guide says there is no universal tolerance value and that an initial good measurement for movable parts is at least 0.3 mm Starting point. It lists what changes the right number:

• the size of the model;
• horizontal or vertical orientation of the gap;
• the geometry of the parts that interlock;
• calibration and slicer settings;
• the material, which can warp or shrink.

Orientation matters because a printer controls the two directions differently. A vertical gap, between two side walls, depends on how accurately the printer places lines within a layer. A horizontal gap, where one surface is printed above another, depends on how the upper surface is laid over air, and it tends to sag into the gap. Expect to need more clearance in one direction than the other on your printer Measure it.

General fit and clearance advice is in Fits and Tolerances, and checking your printer's accuracy is in Dimensional Accuracy.

Keep the gap off the first layer

The first layer is pressed into the bed and spreads slightly wider than the layers above it. OrcaSlicer's documentation describes this "elephant foot" effect: the first few layers print wider than the rest. A joint whose gap starts on the first layer can be fused at the bottom before the rest of the print begins.

• Design the moving parts so their gaps start a layer or more above the bed, for example by raising the joint on a short solid base.
• Use elephant foot compensation in your slicer, which shrinks the first layers inward; Prusa notes it can improve tolerances in some areas. See Elephant's Foot.

No supports in the gap

Support material printed inside a joint fills the clearance and is nearly impossible to remove. Design every surface inside the joint to print without support:

• Prusa's guide says FDM printers cleanly print overhangs between about 45 and 60 degrees, depending on nozzle and settings Rule of thumb, and that short horizontal bridges print without supports. Keep internal surfaces within what your printer can do.
• Where an edge faces the bed, Prusa recommends a chamfer instead of a fillet, because a fillet starts as a very steep overhang.
• Orient the model so the hinge axis and the gaps print in the direction your clearance test says works best.

If the slicer adds supports inside the joint, change the orientation or the design rather than accepting them. More on overhang limits in Supports and Overhangs.

Slicer settings that change the gap

• X-Y hole compensation (in OrcaSlicer) expands or shrinks holes in the XY plane; OrcaSlicer describes it as a way to adjust sizes slightly when objects have assembly issues. A small positive value opens round sockets.
• X-Y contour compensation does the same for outer contours.
• Flow and extrusion width. Over-extrusion fills gaps. Calibrate flow before blaming the design.

Change one of these at a time and reprint the clearance test, not the whole model.

Freeing the joint

Let the part cool fully before you move it. Then work each joint gently back and forth through a small range before using the full motion. If a joint will not free with light force, it is fused: forcing it usually breaks the pin. Reprint with a larger gap for that direction.

Thin pins and knuckles are also limited by wall thickness; see Wall Thickness and Minimum Feature Size.