Cutting all OpenROV parts at FabLab.iMal

Last month I had the honor to be among a small group of people that publicly inaugurated the FabLab of the iMal with the summer workshop on digital fabrication.

During that week we learned how to use the various tools available (3D printer, lasercutter and CNC mill) and we had time to work on our personal projects, and of course I worked on the OpenROV.

Using a laser cutter for the first time

Using the laser cutter is not as easy as it might look at first sight: one thing that needs to really be taken care of is the cutting settings. Too low power and the part will not be cut through, too high power and the size of the cut will be too much and your pieces will be between 0,1 and 0,3mm smaller (or larger, depends on how you look at them) and will not match perfectly when you have joints that relies only on one part fitting inside the other one. Also, since power is a combination of the actual wattage and the speed of the beam, you can achieve the same result with a low speed and low wattage or a higher speed and high wattage. But of course higher speed also means less precision when cutting curved parts, but lower speed also means longer cutting time (and, depending on how the fablab is setup, higher cost of usage).

Another thing to keep in mind is that the same settings will not work the same on the whole surface of the cutter due to attenuation of the beam power: close to the laser source it will cut more than when the plotter is on the other side of the cutting surface. So cutting the whole ROV on just one run was not a good idea because I had some parts cut through, and other that I had to force a lot out of the sheet (and a few times breaking them).

At the end I had all parts cut through, even if not with the best precision (at the end I over-powered the beam to make sure I would cut the pieces, so I bit over-burnt the edges): it’s ok as first attempt at cutting, and when I assemble with glue I’ll try to make sure the pieces stay in the right position.

Alternative method of bending

Once I cut everything, since I don’t have a wire-plastic bender, I experimented a bit with a nice solution someone at the workshop found out: it’s based on the project of a flexible box cut from one piece of acrylic.

Basically a honeycomb pattern is cut into the part of acrylic you want to bend, so that it becomes flexible. I made some tests, and it works well with boxes, but in the ROV than I would need to make it rigid again as otherwise it might start wiggling too much once in water. But I’ll experiment with that solution in the future.

Below here are some of the pics of the various pieces as they were coming out of the laser cutter.

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