A technique for accurate laser cutting on upside-down digital prints.

Among other applications, you can use this to make zero-kerf photo jigsaw puzzles.

Beginners: If you've never made a laser-cut jigsaw puzzle before, learn the easy way first. There are a lot of tutorials on YouTube.

Experienced puzzle makers: Eliminating kerf is straightforward but requires more effort. Larger puzzles are expensive because you need multiple pages.

Any comments or questions may be posted in the Glowforge forum.

90-second video overview

This quick video shows the essence of the precision cutting technique, which can often achive “naked-eye perfect” alignment. (This is also the companion video for Part 1 of the tutorial.)



Jigsaw template generator for 2D pieces instead of 1D edges

Q & A

Is “naked-eye perfect” alignment even possible?

The short answer: Just barely … usually … depending on the use case.

Jigsaw puzzle pieces should be relatively aligned within 0.2mm (depending on photo, resolution, piece size, audience). This method usually gets me 0.2mm accuracy.

Puzzles cut from a single page appear perfect, because if you keep adjacent pieces close together, the relative error cancels out. You mainly have to worry about alignment between separate pages. You can mitigate that problem by taking care in how the puzzle is divided; see Part 4.

Why cut upside-down?

Because in laser cutting, the kerf is always wider on top, narrower on the bottom. For jigsaw puzzles, if you want the kerf reduced or eliminated on the front face, you need to cut it upside-down.

What is this good for?

What is the MAP sled solving (that can’t be solved with a ruler and stationary jig)?

It compensates for these sources of error, any of which can be greater than our target accuracy of 0.2mm:

  1. The position and angle of the printed image on the page isn’t precise.
  2. The scale of the printed image on the page isn’t quite accurate.
  3. The page edges might not be precisely rectangular.
  4. Glowforge’s coordinate system can shift every time it recalibrates itself, and can also drift over time.
  5. Glowforge’s coordinate system can be slightly out of scale, relative to the “real-world” distances defined by your favorite precision ruler. (For me the difference is about 0.1mm per 250mm.)

The sled is designed to directly align the printed image’s boundaries with Glowforge’s coordinate system, without the intermediate step of going through the (irrelevant) real-world coordinate system. The sled is disposable and generally single-use because of (4).