OpenCAL Brings Volumetric 3D Printing to the Desktop

Most desktop 3D printers build objects one thin layer at a time. OpenCAL takes a completely different approach: it solidifies an entire part at once by projecting light through a spinning cylinder of resin. The result is a fully formed object in as little as 20 seconds.

How Volumetric Printing Works

Computed Axial Lithography, or CAL, uses a projector to shine patterns of blue light through a rotating glass cylinder filled with photosensitive resin. As the cylinder spins, light from multiple angles accumulates energy only at the coordinates where the part should solidify. The resin hardens in a single continuous exposure, with no Z-axis movement and no layer lines.

Traditional resin printers cure one cross-section at a time. CAL cures the whole volume simultaneously. That difference eliminates the stair-step surface finish common to layer-based machines and reduces print times from hours to seconds for small to medium parts.

Open-Source Hardware and Software

The OpenCAL project publishes firmware, build documentation, and a parts list under an open-source license. The printer runs on a Raspberry Pi 5, which streams an MP4 video to a 1080p blue-light projector. A stepper motor and rotary stage spin the resin cylinder while the projector delivers the light patterns. A custom three-axis screw mount aligns the optical path with the center of the cylinder.

Builders report a material cost of roughly $1,400, with the projector making up most of the bill. The project partnered with Formlabs and MatterHackers to supply pre-mixed photopolymer resin at cost, so users do not have to formulate their own chemicals.

Safety and Material Handling

Photopolymer resin reacts exothermically during curing and can generate significant heat if left in direct sunlight. The OpenCAL team warns that bulk resin vials exposed to strong light can reach temperatures above 110 degrees Celsius. Work in a well-ventilated area, wear gloves, and store resin away from windows.

Post-processing follows the same wash-and-cure routine as standard resin printing: soak the part in isopropyl alcohol to remove uncured resin, then finish under ultraviolet light. The workflow should feel familiar to anyone who has used a desktop SLA machine.

What This Means for Makers

OpenCAL does not replace a large-format industrial printer for production runs. But it does offer something no other desktop machine can match: speed. For functional prototypes, dental models, or small figurines, the ability to go from digital file to solid part in seconds is a genuine leap forward. The open-source model means the design can improve rapidly as more builders share modifications and test results.

The GitHub repository and build docs are freely available. If you can follow assembly instructions and solder a few connectors, you can have a volumetric printer running in your workshop this month.