CNC Diode Laser & Ablative Techniques

Objective & Introduction

Since 2005/2006, when Instructables.com held project contests with Epilog laser cutters as first-prize, I’d wanted to experiment with high-powered lasers. However, the cost of even the weakest (>10mW) lasers of the visible spectrum prevented me from experimenting.

As of 2020, both CO2 and diode laser module have gotten dramatically more afforable. I had already purchased a 3018-style CNC router (a desktop CNC machine), and adding a laser module was a trivial task. I purchased a Sainsmart 445nm 5.5w diode laser module, and attached it to my machine:

Engraving a digital camouflage pattern into an AR-15 upper and lower receiver using LightBurn software.

Machine Prep & Setup

The 3018 CNC and its derivative models were some of the most affordable CNC machines available in 2020. They’re essentially no more than a T-slot extrusion frame, NEMA 17 or smaller stepper motors, drivers, and metric multiple-lead leadscrews. While they usually operate a router spindle with ER-11 collets, most have PWM outputs on the driver board for laser control.

Adding #10-32 threaded holes for clamps:

Initial circular interpolation of tap pilot holes. Using a 4-flute carbide endmill at maximum RPM. The 3018 would be much more capable if the spindle was capable of higher speeds.

Fusion360 CAM

Cleaning up the tap drill holes with a 1/8″ carbide endmill

Finished tapped bed (powertapped with a hand drill set with a light clutch)

Ablation of Steel & Selective Modification of Material Properties

The 5.5w laser module I purchased isn’t intended for cutting or etching metals. However, I realized that there was, in theory, enough energy concentrated at prime focus to “burn” metals in standard atmospheric conditions.

Ablating a thin line in 0.001″ steel shim stock. This is one of the few materials that I was able to cut unassisted with this diode laser module.

Hobbyist, or semi-commercial-grade lasers typically are not capable of cutting steel or other metals. Fiber lasers can, due to the intense concentration of energy, but they are often prohibitively expensive. CO2 lasers can etch metals, but the wavelength isn’t sufficiently absorbed by most metals, and needs a spray that increases heat absorption.

Ablation of Steel with Reactive Coatings

Instead of purchasing Cermark spray, I experimented with molybdenum disulfide powder “paint”, with various additives, from activated carbon (carbon black would have been superior), to magnesium and aluminum micronized powders). These worked well, but need further research.

Here, I’m burning snowflake patterns into steel shim stock (0.002″) coated with a mixture of micronized molybdenum disulfide powder, elemental aluminum powder (to react with any oxidized iron and reduce residual rust), and magnesium powder.

Ablation with Paint pens:

I also tried using Tag Marker pens to create a coating that absorbs light energy better than (reflective) steel shim stock. These pens deposit a permanent black ink onto cattle ear tags.

Aforementioned Tag Marker, with OD 6+ oxy-acetylene goggles. I’ve long since replaced these with rated laser goggles.

Though the laser cleanly etched through the paint layer, it did not affect the layer below. Nearly all of the coating must have vaporized before the steel could absorb any of the heat.

Attempting to engrave the above test lettering.

Engraving viewed through protective laser goggles.

Ablation of Cerakote

Cerakote is a commonly-applied coating to firearms. It’s self-lubricating, stable at high temperatures, very durable, and possesses high wear-resistance qualities. I made several attempts at ablating this coating:

AR-15 Receiver Patterning

Etching a grayscale image of digital camouflage into the Cerakote coating on an AR-15 upper and lower receiver.

Utilizing Lightburn software, creatively: I manipulated the line spacing, fill angles, feedrates and laser power to etch this grayscale image.

(note: As of the time of this photograph, this firearm’s configuration was legal and in compliance with the letter of the law in the state where I reside. Any changes in the legal environment since this image will be reflected in its configuration.

Shift-Knob

Burning a shift pattern into red Cerakote.

Ablation & Texturing of Wood

I tried both simple, 2-dimensional ablation, and 3-dimensional ablation in wood. I had surprisingly good results with both methods. 2-dimensional ablation was achieved with simple on/off control of the laser; either it was burning at a set power, or not at all:

3D engraving in a section of red oak. Power was modulated through PWM using a grayscale image etching setting in Lightburn.

Etching the brand logo for a local barber on beard brushes.

Drink coasters that I designed in Inkscape, for my grandmother.

Drink coasters for a relative with a ranch.

Ablation and Texturing of ABS Plastic

While this was not pursued in depth because of poor ventilation and concerns about safety, I had good results texturing plastics with creatively-generated patterns.

Pattern generation began with a raster image of white noise, which was then vectorized, and then dithered:

Vectorized white noise:

This generated an image that was infinitely scalable and continuous at all points.

Dithered white noise:

Dithering reduced the resolution and allowed me to operate the laser in a binary mode for speed and burn clarity.

Etching the dithered white noise & other patterns:

I chose to texturize Playstation 4 controllers. Mold markings inside the case indicated that they were ABS plastic (no glass or fiber fill). I used the above dithered pattern and a hexagonal pattern:

Resulting texture effect on the backside of the controllers. The foreground shows a simple grid pattern, while the background shows the result of the above dithered white noise.

Hexagonal patterning/texturing of plastic.

Ablative laser texturing on the 3018 CNC router, using the aforementioned 5.5w laser. This is the hexagonal pattern shown above.

Selective Grain Restructuring of Metals

Though I’ve only begun exploring this topic, metals and other materials can be given anisotropic properties with laser treatment. This involves rapidly heating and cooling (ambient cooling effects, in my experimentation) select portions of a material.

Research on the topic exists as far back as the 1970’s, but has yet to be fully exploited. With enough control over heating and cooling parameters, I suspect that superior material qualities can be generated from fairly standard alloys. Effects can be likened to the process of selective quenching of katana blades, but more precise. Patterns can be used that provide high fatigue resistance in some directions, but high stiffness in other directions.