Guide
Why won't my 3D printed QR code scan?
A 3D printed QR code almost always fails for the same reasons. Check them in this order: in most cases the fix is reprinting in another color or a little bigger.
1. Not enough contrast between the two colors
This is the number one cause. The reader converts the image to black and white: if the two filaments have similar brightness, the code disappears. Fix: a dark code on a light background (black on white is the safest). Try the black-and-white photo test: if you can't tell the code apart in greyscale, the phone can't either.
2. The colors are inverted
A light QR on a dark background scans on many modern phones, but not with every reader. Fix: if the piece is for the public (a restaurant, a trade fair), always use a dark code on a light background.
3. The modules are too small
Each little square of the code is called a module. With a 0.4 mm nozzle, below about 1.5 mm per side the edges get rounded and the modules merge. Fix: make the piece bigger or shorten the content. A long link produces a code with many more modules than a short one, so using the shortest possible address helps a lot.
4. The margin around the code is missing
Readers need a clear zone around the code, in the background color, about four modules wide. If you trim the base or add a frame of another color right next to the code, it may fail. Fix: keep the border the tool leaves.
5. Reflections from the filament
Glossy, metallic or “silk” filaments bounce light back and create white spots in the image. Fix: use matte finishes, especially for the code. If it's already printed, try scanning from another angle or without a light directly above it.
6. Faulty first layer or relief
Blobs, strings between modules or a squashed relief distort the pattern. Fix: calibrate the first layer, enable retraction and clean up the piece carefully. One or two well-printed relief layers read better than many poor ones.
7. The color mixed during the filament change
If some of the previous color stays in the nozzle after a filament change, the first relief layers come out in an in-between shade and contrast drops. Fix: purge more material when changing (with manual changes, extrude until the color comes out clean before resuming).
8. You're scanning too close or too far
A practical rule: it reads well from a distance of up to about ten times the width of the code. A 4 cm QR scans comfortably from under 40 cm; a 10 cm one, from up to a meter. Fix: choose the size based on where people will scan it from.
9. The content has an error
Sometimes the code scans but doesn't do what you expected: the link has a typo, the wifi network has another name or the password changed. Fix: check the content by scanning the on-screen preview before printing. Remember that a static QR can't be edited: if the wifi password changes, you have to print a new one.
Help already built into the code: error correction
QR codes store redundant information so they can be read even when part is damaged. There are four levels: L (recovers about 7%), M (15%), Q (25%) and H (30%). A higher level tolerates print defects or a logo in the center better, at the cost of a code with more modules. That's why, if you add a logo, it's worth making the piece a little bigger.
Quick checklist before printing
- Dark code on a light background, matte filaments.
- Modules of at least 1.5 mm with a 0.4 mm nozzle.
- Clear margin around the code.
- Content checked by scanning the preview.
- Size suited to the distance it will be scanned from.