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Basic design conceptsBeginner18 min

Design parts that print and fit

Test pin-and-hole clearance, explore overhangs and orientation, and choose joints for an assembly.

DESIGN LAB · Learn by doing

A model that looks right on screen still needs space to fit and a sensible way to print. Start with small test pieces, then scale up to an assembly.

Will the pin fit?

Change the hole and pin diameters, then add allowed variation. The 3D model uses nominal sizes; the readout checks worst-case sizes.

Nominal diametral clearance
0.00 mm
Minimum / maximum clearance
-0.20 / 0.20 mm

Transition range: could fit or interfere

Teaching model, not a prediction of your printer. Tolerance is permitted size variation; clearance is the gap you design. Real fits also depend on shape, material, shrinkage and calibration. Print a small test first.

Your turn

Keep the 10 mm pin. Set the hole to 10.4 mm and variation to ±0.1 mm. Check that even the minimum clearance is positive, then assemble.

  • 10 mm pin, 10.4 mm hole, ±0.1 mm variation
  • Parts assembled with guaranteed positive clearance in this model

Keep experimenting. The checklist updates as you work.

Give each layer something to stand on

Tilt the rib, watch how far each layer steps outward, then lay the model flat. Changing print orientation changes how layers build the same part.

Print orientation

Offset per 0.2 mm layer

0.140 mm

An exaggerated stack of layers shows the geometry. The offset number uses real 0.2 mm layers. A 45° overhang is a starting guideline, not a pass/fail limit; test your material and cooling. Laying this straight rib flat removes its leaning overhang.

A bridge spans between two supports; an overhang extends from one side. Short bridges may print unsupported, but length, cooling and filament matter. Inspect the slicer preview layer by layer.

Design the connection, not just the pieces

Start with the motion you want: no movement, rotation, or temporary flexing during assembly. Add locating surfaces, clearance and a way to retain the parts. A lead-in chamfer helps alignment. Split hard-to-print shapes into simpler parts when it reduces support or lets you choose a better layer direction. Layer bonding can make strength direction-dependent; check the real load path.

Choose a joint for the job

Aligns separate parts. Use a hole and clearance, a lead-in chamfer, and a stop or fastener if you need retention. A loose pin alone does not lock the assembly.

A real assembly in FreeCAD 1.0: separate components share pin axes and move together. The tree lists parts and joints rather than one undifferentiated shape.Maxwxyz · CC BY 4.0 · Wikimedia Commons

Words you can now use

Clearance
The intentional space between mating parts; specify whether it is diametral or per side.
Tolerance
The permitted variation from a nominal dimension, not a promise about printer accuracy.
Interference fit
The pin can be larger than the opening; assembly requires deformation or another process.
Print orientation
How the part sits relative to the plate and build direction.

Use it in your CAD

Use dimensions for nominal sizes, offset faces or hole diameter for clearance, and tolerance annotations for permitted variation. Export a short fit coupon before the complete part. In the slicer, compare orientations and inspect supports, bridges, thin walls and layer direction before printing.

Check yourself

Pick an answer for each question.

1. A 10 mm pin and a 10.4 mm hole have what nominal gap per side?

2. Both diameters allow ±0.1 mm. What is the minimum clearance for that pair?

3. An overhang needs too much support. A useful next step is…

Sources (9)

Figures such as temperatures and drying times are typical ranges. Always check the label on your own spool and your printer manufacturer's guidance.