At Steve‘s suggestion today I experimented with coating stainless steel with spray paint and then using the laser to etch away parts of the paint to reveal the metal beneath. I think you’ll agree the results were pretty impressive…
(More directions and pictures after the break.)
Laser etching metal usually results in a darker etch on the shiny metal. To do so we normally use a product called Thermark which fuses to the metal to leave a darker patch. Negatively etching with Thermark would be time consuming and expensive (it’s £50 a can!!!).
The paint I used was Plasti-Kote Stove Black, a black spray paint designed to adhere well to metal. It etched surprisingly well for a paint that’s meant to be resistant to heat.
To get the best coating on the stainless steel, preparation is everything. I first bead blasted the steel sheet to rough it up to help the paint stick better then wiped it with acetone to remove any remaining dust from the bead blaster and grease from my fingers. Next it’s into an oven at 40-50°C for 10 minutes. It sticks better and gives a nicer coating if the metal is preheated.
Once preheated, spray the sheet evenly in a well ventilated area. If you have an oven that can maintain a low enough temperature (40°C ish) place it in to help speed up drying time. At 40°C the paint’s fully dry within 2 hours whereas at room temperature it may take 5 or more. The oven also helps to stop dust settling in the paint during drying.
Once fully dry the painted stainless can be etched. I used a high power (98/100) and a low etch speed (48/400) and a step size of 0.1mm per scan. I used these as a start point for experimenting since they’re the same settings we use on stainless when etching with Thermark. These settings worked well but I found that by upping the speed to 300 got it done faster, still etched the paint away and left a shinier finish to the revealed metal, perfect for the next stage! Electrochemical etching!
A shaft encoder ready for electrochemical etching:
The Hackaday logo, I wanted to see how an image with more substance to it would come out: