OpenCAL brings volumetric 3D printing out of the lab

There is a scene science-fiction fans will recognise instantly: a vial spins, a light flickers, and a whole part materialises inside the liquid. No layer built up one weak line at a time. No support structure to carve away. The object is simply there, complete.3

That machine has left the laboratories. OpenCAL, an open-source project from the UC Berkeley Design for Nanomanufacturing group, documents in detail a CAL printer — Computed Axial Lithography — built from ordinary components and a Raspberry Pi 5.1 2 5

Printing like a scanner run backwards

The technique borrows a principle from medicine: tomography. In a CT scan, X-rays pass through the body to reconstruct a volume. CAL does the reverse: from a 3D model, software computes a sequence of projected images which, crossing a spinning vial of resin, accumulate a light dose exactly where the part must form. The part solidifies in one block while the rest of the resin stays liquid.2

The result: objects a few centimetres across printed in minutes, with no layers, no supports, no peel-off from the build plate.3 4

The core software is VAMToolbox, a volumetric tomography tool that generates the print files the machine consumes.2

A machine you can assemble in an afternoon

What makes OpenCAL remarkable is not just the technique, but the way it reduces the gesture to accessible parts. The firmware runs on a Raspberry Pi 5 (2 GB RAM or more), controlled through a 20×4 LCD and a rotary encoder — so no attached screen is needed to run a print.1 4

The hardware list asks for a compact DLP projector and a Fresnel lens, a stepper motor driven by a Pololu Tic T249, a Pi Cam to record the process, and parts printed on an ordinary FFF printer. The physical files and bill of materials are published.1 4

And here is the detail that changes the experience: printing plays like a video. Print files are MP4s, projected by mpv while the vial spins, and the machine reads the rotation speed directly from the filename.1

What still constrains it, honestly

The project says it plainly: this is in active development, and the resin is the real barrier. CAL chemistry is demanding — it needs a viscous resin, transparent enough at the curing wavelength, with a non-linear response so it cures only where the accumulated dose is high enough. Part of the tuning starts with chemistry, not code.2 4

Surface quality is closer to an older SLA than to a polished shop part. And for now the machine will mostly print volumes of a few centimetres, though larger formats have been attempted.3

Why it matters now

OpenCAL is not the first machine of its kind: CAL dates to 2019, and lab volumetric printers stayed beyond a hobbyist's reach. What has changed is the whole package: open-source software, reproducible hardware, end-to-end documentation, and a Discord community so you are not alone in front of your build.2 4

It is the same movement as RepRap for extrusion printing: making a fabrication technology reproducible at personal-workshop scale, so others do not just use it but improve it.4

The lesson for a maker is not “print objects without layers”. It is: even a process born from medical research becomes tinkerable material as soon as someone publishes the files, the plans and the chemistry. The next OpenCAL may not have to come from a laboratory.