George Smart - M1GEO

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Laser engraving metal using zinc spray

Posted: 16 Apr 2021 07:02 PM PDT
https://www.george-smart.co.uk/2021/...ing-zinc-spray



While looking for a way to create front panels and detailing on homebrew
equipment, I was pointed to a YouTube video by Mark Presling entitled Metal
Finishing With Mark Metal Engraving 101.




In the video, Mark explains how cold galvanizing zinc spray, when excited
by a laser, burns at a high temperature to permanently mark the surface of
the material onto which the zinc was sprayed. Mark suggests that this only
works on stainless steel, however, other videos show how it can be used on
ceramics, glass and similar substrates to burn or melt the substrate. Im
not exactly sure of the process, but, it certainly does leave a
controllable, visible mark on the surface, which is exactly what I was
after!








The box above shows markings for the 144 MHz antenna, GPS antenna, and
status LEDs for an APRS transmitter I happened to be working on at the
time. The effect is to leave a darker surface on the Hammond diecast box,
which (at least to my testing) is very hard wearing and does not come off
with use of solvents



Heres how




Firstly youll need to coat the surface to be etched with a liberal spray of
zinc cold galvanizing compound. I used MOTIP Zinc Spray because it was the
cheapest I could find on eBay and it works just fine perhaps I got lucky
but Ive seen several videos on YouTube each swearing by a different make of
spray, and they all appear to work. The important thing is that it is high
in zinc. Its an epoxy based aerosol, so, spray outside using the
appropriate precautions. The spray should be quite thick, I spray on about
4 heavy coats one over the other and then let it dry for around 5 minutes,
just until the main solvent has evaporated.








While the spray is drying, design your artwork. Im making a line drawing of
the car along with my callsign to put on the box, mainly to see how it
comes out Im keen to see if the line drawing comes out well or not so
watch this space! My design looks like the following:








Next we get to put the metal into the laser cutter. I use a 60W CO2 laser
cutter, with the power set to around 50%. Others have reported success
using 10W diode lasers. I found that 50% was about right for my machine.
Going slowly helped a lot, I reduced the machine to around 5mm/second.
Where possible, vector engrave as the laser power is continuous and more
controlled than raster scanning, but for large areas, such as the text,
raster scanning works fine. I always reinforce text with a vector engrave
around the outer.




Youll need to focus the machine as youd normally do in order to cut the
surface.








Once focused, frame the metal on the cutter bed. My laser cutter has a
spotting laser which really helps with this.








At this point, youre ready to go! When the paint is hit with the laser, it
goes a very burnt/sooty black. The process generates some very nasty fumes,
which you are well advised not to breath this includes metal vapors which
are incredibly dangerous.








Once the engraving is done, leave the work in the cutters fume extraction
for a short while to be sure that the chamber is clear of toxics, and then
remove the work. Mine looks like this:








The final stage in the process is to use a paint remover to remove the
paint from the metal to reveal the final design. I use cellulose thinners,
which works well. Be sure to do this in a well ventilated space, otherwise
you end up with a headache (like I have now, as I write this!).








I think youll agree that the final result looks very clean and tidy, and
has retained all of the detail present in the original design.




This process is quick and easy to do if you have a laser cutter, uses a
cheap-ish (around £6) can of zinc spray, and produces good, repeatable
results with minimal fuss. Its very useful for creating front panels and
similar.




You may also find that spraying another colour of paint over the top, and
then sanding down very lightly will further accentuate the design.