3D printed molds: a practical guide

When a printed mold makes sense

Printed rigid molds are great for wax, soap, plaster, concrete, chocolate (with food-safe coating) and short resin runs. For many casts, or for very detailed parts, print a master and make a silicone mold instead.

Design rules that work

1. Split along the widest part of the model so both halves release (the parting line).
2. Walls of 2.4–4 mm on FDM, 1.5–3 mm on resin.
3. Use 3–6 cone or round locks so the halves line up.
4. Leave a fit gap of about 0.2 mm on FDM and 0.1 mm on resin.
5. Put the pour hole at the highest point and add vents where air gets trapped.
6. Add a flat flange with bolt holes if you need to clamp the mold shut.

Printing and finishing

Print the parting face flat on the bed for a tight seal. Sand the cavity lightly, seal it (epoxy or XTC-3D) for a smooth cast, and always use mold release.

Let the app do the geometry

Sirpam 3D Labs Mold finds the best split, places locks, pour hole and vents, and exports both halves as print-ready STL files.