Lasers, Part 2: The Finishing

Continuing education in laser cutting - May 29, 2018 by Luna

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My first thought when I started engraving things on the Glowforge was "I'll make some coasters!" It seemed like the most straightforward thing in the world: simple flat disks of wood with images engraved on them.

So I cut a coaster and admired it and then panicked at the thought of anyone setting a wet glass on it.

The exciting opportunities of lasercutting: engraving images from basic line drawing to complex photographs, making boxes of all sorts, lamps, resin filled things, sculpture. The bane of my existence: finishing them well enough that a stray drop of water won't destroy all my work.

You can buy wood prefinished for lasercutting but the cutting and engraving breaks through the finish, exposing bare (charred) wood. Sealing this with something impervious to a cup of hot tea turns out to be incredibly challenging and frankly I get why stone is a practical alternative.

microscope image of wood with streaks of brown char
lightly charred wood through a microscope; yes, I took this image just because I can

image of four laser cut coasters with mugs on them
testing finishes with mugs of hot tea

While the various finishes I was testing on coasters were drying, I turned my attention to making small boxes. Fun, cute, and while I'd like them to be resistant to humidity or perhaps an accidental splash of water, not nearly as rugged as a coaster needs to be.

I had a lot of fun with box design, particularly developing the design to make 6 sided living hinge boxes. These had their own set of challenges with regards to finishing: you can't really brush a finish on a living hinge and expect it to bend afterwards. After a few rounds of tests I think I have the box finishes sorted out though (through the wonder of many light coats of spray finish).

various sorts of failed boxes, about a dozen of them
living hinge box iterations which failed in various diverse ways

one small successful six sided living hinge box in walnut in front of various failed draft versions
successful small box standing amid the failures

While the various finishes I was testing on boxes were drying I started tinkering with lamps (aka lanterns or in my original notes "glow box") which are either cut through and covered with veneer to form invisible patterns that only show when the light is turned on or cut through symbols filled with resin that are visible at any time but glow when the light is on.

picking out tiny laser cut pieces with a sewing needle
cleaning up the laser cut image

moon phase pattern cut into wood, with other pieces being attached as sides
the underside of the lamp as it is being assembled

six sided cherry wood top, featureless
lamp top with light off

orange glowing eight pointed star and moon phases design
Moon phase design with lamp lit

In a weird twist, the lamps have actually been the easiest to finish--although the most time intensive to make by far. The boxes are coming together and I'm pretty confident I'll have those in a final form within the next couple of weeks. The coasters I have shelved indefinitely as being too problematic to make in wood for now. I might do a post sometime about the various problems that emerged in coaster finishing and why it's not as simple as "brush on some polyurethane" which is what I initially, naively expected to work.

Seven pointed star with flames around it filled with white resin in cherry wood
Glow in the dark resin

There's still the occasional art piece which doesn't require a durable finish, of course, like the valentine I made.

Crow, anatomically correct heart and a short poem laser cut in wood. Text: Cardinals are red, I am quite the birder; the Crow calls your name, it's time for some murder by Chuck Wendig

And photo engraving is frankly its own art form.

Photo by Tim Edmonson

photo of Mayan pyramid with a tiny person standing in front
engraved photo

Though I did need to seal this one for humidity since Tim lives on some Florida beach or something.

The last six months have been a lot of trial and error, especially for finishes. I'm thinking about making a video to spare others some of the tedium and expense of discovery but for now I'm at Cin_Nic on Twitter if anyone wants to talk about lasers and what happens when they encounter wood.