A photopolymer 3D printer for the cost of one minimum wage
In 2015 filament printers were already affordable, but resin printers, with much better resolution and finish, cost over 3000 US dollars. This project built one from common parts: a video projector as the light source, a mirror, a vat with a transparent bottom, and the electronics of a filament printer. It cost about 646,000 Colombian pesos, projector not included, and produced parts with good surface finish at the price of long exposure times.
Context
In photopolymerization, each layer forms when a liquid resin is illuminated with the image of the part's cross-section. The resin cures where it receives light. With a projector the whole layer is exposed at once, and in-plane resolution depends on the size of the projected pixel.
The delicate step is peeling. The freshly cured layer sticks both to the build platform and to the vat bottom, and it has to be separated from the bottom without breaking before moving to the next layer.
Design
The printer projects from below. The projector points at a tilted mirror that directs the image to the vat bottom, and the part grows hanging from a platform that rises.
Printer model with its main dimensions
- Frame of aluminum profiles with 3D-printed joints.
Profile frame and vertical-axis carriage
- Vat of aluminum with a glass bottom coated with a layer of transparent Sylgard 184 silicone, to which cured resin adheres weakly. The vat tilts by means of a belt to peel the layer progressively, from one edge to the other.
Vat with silicone-coated transparent bottom
- Build platform on a threaded rod with an anti-backlash nut.
Build platform mounted on the vertical axis
- Electronics based on an Arduino Mega with a RAMPS board and stepper drivers, the same as open filament printers. Control was done with the Creation Workshop software.
Calibration
Projector and mirror alignment, the millimeters-per-pixel scale, the tilt sequence and exposure times were adjusted in sequence.
The projector emits little ultraviolet light. With one second of exposure, the usual value, the resin did not cure. The first good print needed 50 s per layer. After several trials this came down to 27 s per layer, and 45 s for the first layers to ensure adhesion to the platform.
Results
First print with good finish, though with defects in the first layers
Ring gear and pinion printed after adjusting exposure
The final parts have good finish and reproduce fine details such as gear teeth. Total cost, about 646,000 pesos, was close to that year's monthly minimum wage, which was the target.
What is missing
The thesis reports no measurements of dimensional accuracy or resolution, so quality is assessed visually. At 27 s per layer, speed is low compared with commercial equipment, and the cause is the light source: a video projector is not made to emit in the ultraviolet. The projector and the resin are not included in the cost tally.
How it fits in Robiolab
This project belongs to the digital-fabrication line through which the group built its own manufacturing capability between 2014 and 2016, together with the filament extruder and the electrospinning printer. It is not a robotics project, but stereolithography later became the tool for making small, precise parts in lab projects, such as the force sensor of the prosthetic hand.