There’s always a next step, a new opportunity to learn. For me, that’s the best part of being a maker. I’d wanted to come up to speed on 3 modern fabrication technologies, a filament 3D printer, a resin SLA 3D printer and a CNC router. At the Columbus Idea Foundry, a local makerspace, I had access to these devices. That led to my article, published on MakeZine in January. I wanted to understand the strengths and weaknesses of each of these technologies and as a beginner with them all, it was the perfect chance to compare.
My comparison project was to create an enclosure for a “Camera Axe,” a camera controller for high-speed photography developed by another maker, Maurice Ribble. I’d built the board from a kit. While it worked perfectly without an enclosure, it just seemed wrong to use it “naked.” But this was a challenge, the board was not designed with an enclosure in mid. ICs and capacitors stood taller on the board than the switches used to control it and the LCD display. Not an easy task.
My colleagues at the Idea Foundry were delighted with the article but they wondered why I’d stopped at 3 fabrication technologies. What about our Trotec Speedy 400 Laser cutter/engraver, they wondered. And so round 4 began. I’d never used a laser cutter either.
In comparison to additive approaches like 3d Printers and subtractive techniques like CNC routers, working with Laser Cutters is a different game altogether. One might call this fabrication model “assemblative.” Laser cutters can’t create cavities so creating an enclosure requires cutting an assortment of parts and assembling them. But as I looked at laser cut enclosure designs on the web, I was bothered by their appearance. Some looked like sandwiches gone wrong, with the height of the enclosure provided by many stacked layers of acrylic. Others seemed more like3d jigsaw puzzles with the sides and top made of interlocking parts. I wanted to produce an enclosure with a more professional look. As before I also wanted to create the enclosure using only one tool, in this case the laser cutter, and limiting myself to fasteners as add-ons. I chose acrylic sheet as my material, both because it is relatively easy to cut and because I had a source of inexpensive scrap at a local distributor.
Having worked in the world of true 3d, rethinking the design as a set of planar surfaces seemed very restrictive. As mentioned above, this enclosure needed to accommodate a range of bumps and recesses. What would I be giving up? In some ways, the step forward seemed simple. Just use Fusion 360, my 3d CAD software of choice, eliminate any chamfers on horizontal surfaces and then cut the enclosure into planes. I’d then just cut out each plane on the laser cutter. A top, a bottom and 4 sides.
But thickness is infinitely variable in a 3d print. Acrylic sheet comes in defined thicknesses, 1/16”, 1/8”, etc. My original design had recesses in the top to make the buttons accessible and recesses in the top’s underside to accommodate the parts that projected above the height of the tall buttons. Since the laser cutter can’t create recesses in a surface, each of those levels would require its own piece of acrylic. But then too, the variance in height wasn’t necessarily 1/16” or 1/8”. This was going to require a good deal of experimentation, both in the CAD tool and with actual prototype parts.
After a couple of iterations my design came to look like this:
Taking a part from CAD design to production with a 3d printer or CNC router is a two-step process. For example, with the Lulzbot TAZ printer, the design is exported from CAD and imported into Cura where it is prepped and then sent to the printer. Going from a CAD design to the final product uses with the Trotec laser system is a 3-step process.
- Export the drawing from the CAD tool
- Import the design into a vector graphics program where specific colors are assigned to define the areas to be engraved or cut
- Print the file from the vector graphics program which triggers the Job Control software to load. In that tool, you then position the laser, position the part, define the laser’s speed and power for each area of the design and then kick off the job.
In that setting of speed and laser power, laser cutting shares another common feature with CNC routing. In the world of CNC, “feeds and speeds” are a bit of an art form. What material is being routed? How fast should the bit be spinning? How many inches/second should the router move? How deep should each pass be? Settings for the laser cutter are similar. What material are we cutting or engraving? How fast should the laser move across the material? What percentage of full power should be used? And at what frequency should the laser pulses hit the material? As with the CNC router control software, the Trotec Job Control software incorporates settings for a wide range of materials. Still experimentation is needed.
The Trotec laser uses a vector graphics editor as a design tool. I had a copy of Corel Draw so that was my tool of choice. But how to get a drawing out of Fusion 360 and into Corel. Corel does accept CAD drawings in DXF format (only the pro version, not the Home version). But for the life of me, I couldn’t find a way to export a DXF out of Fusion 360. After far too many wasted hours I learned that you have to turn off “Capture Design History” to export a DXF file from a sketch. This makes no sense to me and is a significant headache. Once you turn off history to do the export, you can turn it back on but you will have lost all previous design history. Ugly!
The middle section of my design (between the two top layers and the bottom) stood about 1 inch tall. My initial thought was to cut it out of one block of 1 inch acrylic. That seemed like a good idea but I ran into two problems. First, the walls on the sides need to be quite thin to handle allow inserting 3.5mm cable ends into the board’s jacks. I was concerned that those thin walls would deform under the heat of the laser. So, I split that level of the design into 4 components, two endcaps and two side walls.
I still wanted to create the endcaps out of 1 inch acrylic. I ordered a 12-inch square of 1 inch acrylic online, but once I tried to cut it, I encountered the second problem. The Trotec Speedy 400 is a powerful laser cutter/engraver, with a 120W laser….