I'm currently an aerospace and mechanical engineering PhD student, and found out at the beginning of the spring semester that they wanted me as a teaching assistant - TA - for our undergraduate senior design course. Students have to design, build, and fly an RC aircraft with certain payload in our sports arena (an indoor dome - free kudos to any who guess the right college!). Since I'd done my undergrad and masters at that college (going for a triple-sweep) and built a solid plane, the department decided to give me the keys to our laser cutter room.
[Insert mad scientist laugh here]
Seriously. They gave me the keys, and said have fun...not in so many words, but since nobody in the class could cut parts for two months, and I had to *learn* the control programs...well, let's just say I knocked out a couple home projects, all in the name of material and settings testing. The previous TA taught me enough to run the machine and control software (Adobe Illustrator), but didn't know proper vector powers or speeds, so I figured it was "two birds with an expensive 40 Watt laser" time.
All in all, it was a fun semester helping the students, and I learned a lot about laser cutting and proper image setup. There were some obvious issues with my methods - mostly vector line clean-up problems and path doubling (which actually was a great mistake - you'll see why) - but between helping seniors with airfoil and fuselage CAD parts and my random test cuts, I made a good chart of material / thickness / laser power / laser speeds and some nifty art to boot. Since I'll most likely run this class next year, too, I'll have time to stock up on some more art ideas...
Step 1: Pre-Process Desired Image (1)
But vectors...so, so easy for aircraft parts, but so annoying for jagged edges. The rudder plate shown here was directly exported from Pro/ENGINEER (my go-to CAD modeler - yes, I prefer its overly complex GUI to Solidworks, Inventor, Sketchup, whathaveyou...I've used it for everything from designing RC aircraft to outdoor storage sheds with full Mechanica stress analyses), and only contains vector pathlines by default - that's the one great thing about DXF (Drawing Exchange Format - AutoCAD's vector plotting format). But a jagged or wrinkly edge like in my fern? Needs some pre-process loving and careful manipulation to get an optimum path.
Too bad I didn't know any of that going in - the fern was my first fully-custom cut pattern, so after Google searches and reading a few tutorials, I did what I always do...brute force trial-and-error. Not always the best method, admittedly, but hey, I'm an engineer. It's not like I've spent seven years of my life learning how to approach problems elegantly...
So! To get this file running as quickly as possible (since I'd thought students would want cuts before Spring Break...I was optimistic by three weeks), I did some simple photo manipulation using my favorite starting program, Paint.net. Not as powerful as GIMP or Photoshop, but I'm not a fan of the former's poorly-customizable plugins or the latter's price, and Paint.net is more than sufficient to get to the next program (Inkscape). My first step was to cut a single board out of the picture and size it to the wood template I'd be laser cutting (24" x 12" x 1/8" birch plywood). This had two side benefits - first, I wouldn't have to deal with vector scaling in Inkscape (well it's very accurate, it's too easy to miss a single node and screw up your image), and second, it filtered out unnecessary details. This wouldn't usually be a good thing, but for this image it magnified the shadows on the wall, which were better representations of the fern's wiggly edges.
It also allowed me to rapidly size the leaf to its proper laser cut board size, by scaling and using black-space to approximate the full leaf size (seen in the intro step). Naturally, this was overlooked when I took the file to the cutter and overscaled...since I'd forgotten to bring the JPG of the original leaf with me to my control computer...so my final piece (the left-hand leaf) was almost 30% too large...go figure. But hey, I never said this would be a perfect recreation. The other two boards came out true-to-life after more careful scaling.
Step 2: Pre-Process Desired Image (2)
The third and final layer (vector-path design) was built by copying the second layer and recoloring the whole page into black-and-white to only show the edges. Unfortunately, my vector pathing program (Inkscape) didn't like my formatting - I had some non-closed loops, so it wouldn't detect all the edges properly, and my line thickness varied too much to develop a good, single-layer path. Hence my epiphany - I'd read on Inkscape's tutorials about a different edge-detection choice that traces bitmaps rather than using the plugin I'd been working with. Yay, bitmaps are easy to generate. So I filled in the edges in Paint.net to create a high-contrast silhouette-esque bitmap (BMP). For the other two leaves, I simply "magic wand" selected everything but the holes, then inverted my selection to color the holes pure black, giving a great, accurate silhouette. Problem solved!
...problem not solved. Problem not solved at all.
Step 3: Pre-Process Desired Image (3)
Not truly, but it looks that way. Buried in Inkscape's FAQ is the fact that you need to delete the original image after edge tracing - it leaves it in place, rather than hiding the original BMP, so after frantically trying every bitmap tracing protocol and seeing nothing work, you finally in frustration delete all the overlying maps and voila! Your edges appear! Thanks Inkscape. You couldn't overlay the new lines in a different color?
Second issue - by default, Inkscape defines a double path if your BMP features aren't fully closed (with this built-in algorithm - there are optional plugins if you like more control). If you defined your BMP in a vector illustrator (like Illustrator or Inkscape), then your filled-in sections are going to be fully closed - you have no gradated pixels fading from your working color to your background at the edges (black to white here), so it can define a "perfect" edge. In my case, I have a clearly white background, a clearly black internal segment, and a gradated gray line between the two. Edge detection picks up the two sharp colors, and makes a double path.
This is an issue if you're working with very fine details (i.e. inlays that need tolerances < 0.01" - just use a direct CAD output for tightness), but in this case, it turned out to be a blessing in disguise (next step!). I tried deleting the internal paths, but in Inkscape it's a pain to select closed loops and nothing else. Whatever...I figured either the laser would make the cuts properly - a good chance to test the laser size and resolution - or burn away the excess, creating nice dropout pieces. So instead of cleaning the image fully, I just exported as a DXF and called it a day.
Step 4: Process Cutter File in Control Software...and LASERS
So, I was stuck with the house control software - Adobe Illustrator. I hate this program - in fact, I dislike most Adobe products (for very specific reasons) - but Illustrator just gets under my skin. For a vector/raster plotter that specializes in DXF compatibility...it can't read DXFs. Let me reiterate that - there are 30 or so industry-standard CAD modelers and dozens of freeware and student versions, and each produces a slightly different DXF header. That header is between 1 and 20ish lines and is completely dependent on the host program. It's relatively meaningless to all vector programs, and since many DXF builders exclude commented headers altogether, you'd expect Illustrator to ignore everything before the first valued line. Nope - of the 70 or so airfoil files uploaded by my students, roughly a third couldn't be read natively - and many of those were built in AutoCAD...the only truly native DXF builder. Illustrator also doesn't like SVGs (Inkscape's native), or many types of PDF (Adobe native...hmm...), or half of the other formats my students worked with.
Yadda yadda complaining aside, at least the Epilog control package was easy enough. All I really had to do in Illustrator was resize the template, resize the DXF, set the vector line width to 0.001" (default for our control as cut-through), and play with the speeds until I had a good single- or double-cut pass running. Oh, except for Illustrator not keeping the native DXF sizing as exported by Inkscape - hence why my 1st (left-hand) leaf was oversized...I manually scaled the other two by eye.
No pictures of the cutting process - suffice it to say that 15 minutes per cut (1/8" birch ply on this machine required laser speeds of ~20% and power ~100% for 500 Hz, 600 dpi - I could have pumped the frequency and resolution, but air assist did not work all too well, so I played it safe) and rocking to Metallica didn't leave much time for photos. Neither did the fact that every time I turned on the laser throughout the semester, I'd gather a crowd of watchers...or I'd find myself chanting "laser, laser, laser!" while watching...
But here was the nice bonus. You can see the cutouts from the double pathing - almost all of the large inside cutouts dropped onto the laser bed with a light tap (although a few didn't cut fully where the boards were warped), and they were surrounded by these very thin (millimeter or thinner) cutouts (raceways). In spots where there were tiny paths within these raceways, the laser cut minute holes (second image) - a nice way to check the laser thickness and calibration. Plus, these raceways were burned enough in the unfinished cuts that I can knock them out with a chisel without damaging the board face. Chock that up on the to-do list.
Step 5: Clean Up Art Boards
A note on materials - I limited my original choices to the woods available to my students (balsa, ply, bass). During my testing process, I made practice cuts in varying balsa grades, bass, outdoor ply, hobby ply, birch and beech ply, mahogany (we have a great art supply store!), cherry, walnut, and cardboard. The laser could also handle thin acrylic sheeting and MDF. Unfortunately, most of the exotic materials were only available cheaply and locally in 3" or 4" x 24" or 36" strips of various thicknesses, and as a first test of both the laser and my vector pathing skills, I wanted to run as cheap as possible. Birch and craft ply (2 and 1 sheets, respectively) were bought at a local Hobby Lobby for 5 bucks a pop in 24" x 12" x 1/8" - this also checked how close to the bed edge the laser could cut. If I'd known basswood was available in 24" x 12" x 1/16" sheets at a closer store for even cheaper ($2 a sheet), I'd have tried bass instead - it tended to cut cleaner with less charring and considerably less smoke. But $15 and free laser access can't really be beat.
Step 6: Paint Art Boards and Apply Backing
For birch ply, I've found in the past that cheap gray spray paint primer (Valspar is my favorite for wood projects, but Krylon and Rustoleum are fine - Valspar has better spray nozzles and less sputtering, but you can use graffiti nozzles if you want texture) followed by a colored spray enamel and then a clear-coat enamel work best. We might try using Gesso as the primer, though - my mother paints with oil-acrylics and uses Gesso heavily on canvas, but since that stuff just rolls on and sticks to everything under the sun, it might be easier. You can also mix in textured Gessos for different looks - beach sand, pebbled, fibrous, dendritic...our art store has many textures - so we can play with the final product. Spray paint adheres to Gesso as well as to primer (plus you can use oil-acrylics or pure acrylic paints for highlights if you want more details), so go nuts!
For a backing board, depending on the laser cut board weight, the simplest material is cheap craft-grade foamboard (foamcore). A little bit of wood glue or (for heavier boards) two-part epoxy will bond well enough, and since foamboard is cheap and light, you may be able to get away with Command strips or simple double-stick tape for hanging. Our ply boards are a bit too thin for hanging brackets (although small holes in the corners to hang on brads or staples could work), but should be light enough for non-permanent sticky pads. Foamboard is also paintable, so if you can't find a good base color, spray or paint away! For heavier cut boards, another piece of plywood (slightly thicker to allow brackets), heavy balsa, or even corrugated cardboard could work well.
Pictures ahoy as soon as they choose some colors.
Step 7: Bonus Pretzel! Make Secondary Art With Pop-out Pieces!
Lessons learned time! Allergy-prone people should never laser cut plywood without wearing a fume mask - even having a fume hood and good ventilation didn't save me. Immediately after cutting the first leaf, I was struck down with allergies from hell...that almost progressed to a full sinus infection. Balsa and basswood smoke was no problem, but the glue in this ply (standard finishing-grade birch ply from Home Depot) just hit me hard.
Step 8: Update Ahoy! Readying Torpedoes for Final Approach! ...I Mean Crafting Materials...
To save time, they purchased a few sheets of craft paper from our local Michaels and some plain white poster board to use as a backing. The plan was to adhere the green paper to the back of the wooden boards with spray adhesive (a can I had lying around from another project - soon to possibly be a new Instructable), then stick the poster board behind the green paper (either with the spray glue or double-stick tape) for the wall mounts. The green paper was slightly too thin to trust to normal mounts (like picture hanging tape stickers, Command velcro strips, or hanging hardware), so the poster board would add another, stronger layer that's less likely to peel off - especially with a good adhesive coating.
But before all that, the boards needed to be colored. Instead of paint, they chose two media - white Gesso (my mother paints in oil-acrylics and uses this for canvas prep) and modeling paste. The Gesso was applied first with a roller for a nice primer coat, then the modeling paste was added with a plastic fork (to get uneven splotches in place) and smoothed with a roller. This gave a stucco-like texture to the boards that mirrors the ceiling nicely and breaks up light on the surface, adding a bit of depth to the piece. This can be seen much clearer in the pictures in the next step.
Step 9: Adhering the Backing and Prepping for Mounting
After the glue had set, the white poster boards were sprayed with adhesive and the fern pieces plopped and pressed in place. Then came the very frustrating, very sticky part - trying to cut around the edges of a still-tacky poster with a craft razor knife. Ugh. Turns out the glue takes only seconds to tack, but about an hour to be completely dry to touch - an hour we didn't want to wait. Bad choice. I could have just used good scissors in a straight cut, but to avoid peeling the paper or cutting inward on the open leaf sections, I decided a razor knife would be easier. And admittedly, it wasn't difficult to cut through the craft paper and poster board, even with the glue. No, it was the lack of a sufficiently sized cutting board that made life painful. Our only large cutting board is textured glass - great for slicing meat with ceramic or steel kitchen knives, but death on razor edges - and my good self-healing rubber cutting mat was who-knows-where, so I resorted to one of the small plastic kitchen cutting boards. It meant shifting the board every 30 seconds - I still managed to gouge the table I was using a few times - and realizing one annoying point...
My razor knife slices through plastic cutting mats like a lightsaber through a tauntaun's belly.
Oh well. Anyway, after slicing away the excess poster board, the ferns are now ready to hang. The last image of the night shows the finished product against their destination wall. All we have left to do now is add our chosen hanging pieces - plastic velcro Command strips (like the industrial, all-weather 3M plastic Velcro used for hanging heavy picture frames and outdoor decorations) - and pop the boards onto the wall. They'll be staggered like in the intro images to get the idealized effect, but we'll have to play with spacing. We need a nice, sunny day before we can hang these - our garage (den) has large skylights that can flood the wall with bright light much of the day - so finalized images are forthcoming.