How do I cut a jigsaw puzzle on the CNC so the pieces actually fit together?

The idea

A router bit removes a strip of material wide as the bit, so the pieces only fit if the cut is tuned. The published build below cut every piece with Profile toolpaths, spread over several sheets, and then tuned the fit with a small negative profile offset found by test cuts.

A published build you can copy

The software maker published a customer case study of a 400 piece, 500 mm square puzzle cut in VCarve Pro. The steps were:

1. Generate the puzzle vectors with a free jigsaw generator and import them.
2. Close any open vectors.
3. Arrange the pieces over several sheets (five sheets of about 16 x 14 inches in that build).
4. Create Profile toolpaths and cut.

Settings reported for that build, in 12 mm solid surface material (Corian sink cutouts):

• 1/8 inch two flute upcut spiral bit
• 8000 RPM, 70 inches per minute feed, 40 inches per minute plunge
• 1/16 inch depth per pass
• A negative offset on the profile toolpath of 0.05 mm to start

Tuning the fit

The fit is found by test cuts, not by a formula. In the case study the first setting gave a snug fit. After a bit change the pieces were too tight, and the offset was changed from negative 0.05 mm to negative 0.09 mm. The lesson: any time you change the bit, cut two test pieces before running a full sheet, because a tiny difference in real bit diameter changes the fit.

Holding 400 small pieces

No tabs were used. The maker masked both faces, glued the blank to the spoilboard with the tape and super glue method, and set the cut depth to 12.1 mm so the bit just touched the first tape layer. The pieces stayed put. The finished pieces were too heavy to go up the dust collector, but the maker notes the small waste pieces could have caused trouble if they had come loose.

Pro tips

• Cut a few spare pieces on the last sheet to replace any that chip.
• Assemble the puzzle as pieces come off the machine. The maker then remounted the assembled blank and carved a 3D design across it.
• A stable material matters with parts this small. Use the numbers above as a starting point only and test on your own material.
• See the entries on holding small parts and on the tape and glue hold-down method.