In the maker space, not all wood is created equal. Often times makers use readily available materials for laser cutting like plywood or MDF (Medium Density Fiberboard) which are both manufactured wood materials and easily obtained at your local building supply store. Although these materials are in fact wood, they have different characteristics than say a raw piece of wood like a burl harvested from a tree or a solid piece of Oak. These manufactured materials and their different compositions present some interesting challenges that novice makers should be aware of.
I learned an interesting lesson about both materials and technique when engraving a Birch plywood game board I created as a gift for a friend. Birch plywood is a staple material among laser cutting enthusiasts and I had designed mine with the typical alternating colored squares in a checkered pattern. The final design had a letter P inlay-ed into the middle of the board, his surname begins with a P, and it also had some text and a fancy scribe detail along the edges. I was happy with the design and I felt good about being able to pull it off with the laser.
Next I decided to do a few tests, I knew I was going to have to run a few scrap pieces to get things correctly dialed in but my early tests almost completely derailed my project before it even began. I found when trying to engrave the dark color I needed for the dark squares, I figured hotter (to get darker) would be better and attempted to etch the color into the wood with a good burn. This is when I experienced first hand the perils of working with a composite and/or laminate material, the power setting I chose paired with the material I was working with did not result in what I had desired.
Example of heavily engraved surface exposing the laminated core.
My initial power level had engraved clear through the wood veneer and left a rough and inconsistent finish on the dark squares which was NOT the affect I was trying to achieve. Compare the roughness of the dark squares to the smooth finish on the light squares. Once I saw this for myself, it was clear that I had a problem with my assumptions and it was going to take more experimentation to get this right.
So, let's pause there and talk about plywood. Plywood is in actuality a combination of things. It is a composite material made up of alternating layers of wood and glue, compressed together and bonded under pressure, It also could have the following characteristics.
- The outer most veneer layer is the finish material and likely of a higher quality than the core material that it is bonded to (don't engrave beyond this layer if you intend to retain the veneer quality)
- The individual plies (layers) can sometimes be of a completely different material and act differently than adjacent layers when cut causing unexpected behavior and results
- The wood grain direction is usually rotated relative to the adjacent plies for structural stability so the wood grain changes direction the deeper you engrave into the wood
- The bonding of plies is accomplished by glue and the glue has it's own reactions and resistance to being cut by the laser and best avoided when engraving
- Random flare ups - caused by the reactions of randomly distributed glue, wood density (like a knot) or a combination of the two when hit by the laser
- Unexpected finish/texture - caused by engraving through the veneer and exposing the lower quality core material
- Incomplete cutting - caused by changes in the wood composition, usually due to the core materials and glues, kind of the opposite of flare ups
Ultimately I experimented with lower and lower power settings until I achieved a very rich color treatment at just 5% power which, by the way, was enough to color the wood, retain the wood texture and not remove the veneer material in the test piece below which ultimately resulted in a higher quality piece. Your settings will vary but don't be afraid to try new things, work with the materials you have on hand and push the limits of what you already know. Experimentation is key to discovery and mistakes teach us lessons (or skills) we might not otherwise learn.
The finished piece had a richer colorization as shown in the image below.
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