Connections in depth: Bolted, Hinged, Snapped, Sliding, Glued, Geared, Press-fit

A Connection tells Solid Vibes how two pieces are held together or allowed to move. It drives the motion playground, the interference check, the Make list, and the details the agent adds (screw holes, hinge knuckles, snap hooks).

The clearance numbers below are starting points for FDM printing with a 0.4 mm nozzle. Tolerances and fit explains how to tune them for your printer.

Bolted

Pieces are held together by screws, bolts, nuts, or heat-set inserts.

Best for: anything you will open more than once, and anything under load.

What the agent does: "Fasten these" picks correctly sized screws and the matching holes, bosses, or inserts. Holes can be clearance (screw passes through), tapped, counterbored, countersunk, or heat-set.

Rules of thumb:

• An M3 clearance hole is usually 3.2 to 3.4 mm; for printed holes, which tend to come out slightly small, 3.4 mm is a safe choice.
• For plastic, a heat-set insert gives a far more durable thread than printing the thread, especially for parts you will open many times.
• Keep at least 1.5 to 2 mm of material around a screw hole.

Fasten the lid to the box with four M3 x 8 screws into heat-set inserts in the corner bosses.

Hinged

One piece rotates relative to another about an axis, within limits (for example 0 to 110 degrees).

Best for: lids, flaps, folding arms.

What the agent does: Adds hinge knuckles to both pieces and a pin or bolt, then sets the angle limits. Moving the Thing in the playground shows where the hinge binds.

Rules of thumb:

• Give moving surfaces 0.3 to 0.4 mm of clearance per side, more than a static fit.
• Leave room for the lid to swing: the corner of the lid sweeps an arc, and it can collide with the box at wide angles.
• A hinge pin along the print bed prints stronger than one standing upright.

Snapped

A flexible feature (a snap hook) clips into a catch.

Best for: tool-free lids and battery covers on parts that will not be opened often.

Rules of thumb:

• Cantilever snaps should be long relative to their thickness. A hook arm of roughly 5 to 10 times its root thickness bends without breaking.
• PLA is brittle and snaps fatigue quickly. PETG, ABS, ASA and nylon forgive more.
• Orient the print so the layer lines run along the length of the arm, not across it.

Sliding

One piece moves along a straight line within limits, measured in millimetres.

Best for: drawers, sliding lids, adjustable stops.

Rules of thumb:

• Use 0.2 to 0.3 mm clearance per side for light, smooth sliding.
• Dovetail or T-shaped rails hold pieces together while sliding, so they do not lift off.
• Add a small stop at the end of travel so the piece cannot fall out.

Glued

Permanently bonded. Common when you split a big model into printable halves.

Best for: multi-part prints larger than your bed, laminated panels.

Rules of thumb:

• Glue bonds best on large, clean, flat surfaces. A tiny tip of contact will fail.
• Add alignment features such as pins, a tongue-and-groove, or a dovetail so the halves register correctly while the glue cures. Splits can include these joints for you.
• Leave 0.1 to 0.2 mm of gap per side for glue to flow, when using liquid adhesives.

Geared

Two or more gears mesh with a defined ratio.

Best for: transmissions, dials, small mechanisms.

Rules of thumb:

• Center distance between two spur gears equals module times the sum of both tooth counts, divided by 2.
• Printed gears need a little backlash, around 0.1 to 0.2 mm, or they bind.
• Gears that mesh must share the same module (tooth size).

Add a spur gear with 20 teeth and module 1.5 on the motor shaft, meshing with a 40-tooth gear on the output. Add 0.15 mm of backlash.

Press-fit

Held together by interference: the shaft is slightly larger than the hole.

Best for: bearings in a housing, dowel pins, inserts.

Rules of thumb:

• On a well-tuned FDM printer, interference of about 0.05 to 0.15 mm gives a solid press.
• Press-fits are sensitive to your specific printer. Always print a small test piece first.
• Do not use press-fits on thin walls, or the wall will crack.

Limits, checks and the Make list

Every Connection can have limits: degrees for rotation, millimetres for sliding. The playground and the interference check use them. The interference and tolerance check is tuned to the process you chose, so a gap that is fine for CNC can be flagged for FDM.

Each Connection's hardware (screws, inserts, pins) lands on the Make list, so you know exactly what to buy.

Choosing quickly

Try it

On the Hinge box template:

Add a snap latch on the front so the lid stays closed. It should release when I press the tab with my thumb. Use clearance 0.3 mm per side and keep the print PETG-friendly.

Accept the ghost, then grab the lid in the motion playground and watch for collision flashes.