3. Computer-Controlled Cutting

Group Assignment

We were 4 on the group assignment:

• Antoine Jaunard
• Bruno Molteni
• Marco Cataffo
• Roger Anguera

Our idea was to use one of the Trotec machines, either the 100 or the 400, but they were being used all morning by other students, so after waiting for a while we finally decided to do it on the old and huge Multicam 2000. Our instructor Mikel Llobera helped us throught the process. This would have been really impossible without him, given the complicated interface of the machine, not to mention that some parts of it are not working properly.

Our first step was to find a template that included different types of cuts, engravings and rasters all on the same piece. We found this one and opened it with Rhino, to prepare it.

On the multicam, you have to go through it's own software called EnRoute, that turns a DXF file into gcode that the machine can read. With EnRoute open and connected to the machine, you can load the file from it's 1980's-style handheld interface, which is both cumbersome and amusing at the same time.

Once we had the piece on EnRoute, after a few crashes of the software due, we think, to the amount of different lines on the design, we learned that we would have issues with raster on that machine, so we had to remove the parts of the design that were supposed to be rastered (in this case, the classic wheel with strength percentages)

When the file was ready on EnRoute, it was time to prepare the multicam for cutting and engraving. The process we followed is more or less the following:

• Align material on one side of the bed.
• Set 'home' to one corner of your material.
• Configure jog speed - This is how fast the head moves when travelling.
• Set laser header distance to the material by moving the laser head down until the calibration piece touches the material.
• Select material from material library. We chose cardboard
• Enter material thickness - in our case, 4mm
• Select cut mode (cut/engrave/raster)
• Select cut pressure - This is the amount of air blown into the material to prevent fires.
• Set the speed and power values: We started with 150/100 and it caught fire. So we lowered it to 100/100 to cut and then used 60/100 to engrave.
• The result piece looked like this. Pretty good after all !

The last part was calculating the kerf, so what we did was design a piece with 10 cuts and cut it, press all the pieces together, measure the gap left on the edge, and divide it by the number of pieces. In our case, we got a kerf value of 0.15mm

Laser Cutting

Sketching out the idea

For this assignment I wanted to create something a bit more useful than just a press fit kit, so I started sketching a modular stand with adjustable angles, using 2 pieces with press fit forming an X as the base and a third piece on top. I started playing with the idea of a new press fit joint using a inner hole where the other piece goes through and having slots on both sides of the piece that goes through.

Gone 3D

I first created a hand cut cardboard prototype to test the idea and using it I managed to finish the design of the different pieces. With this in hand I started creating the model on freeCAD using the Part Design and Sketcher workbenches. I first created a sketch for each piece, and created a single shared spreadsheet with the different parameters for the pieces, such as height, thickness, slots width, kerf, etc. With this parameters I started to make the holes in the pieces using constraints to make the model parametric.

Cutting it up

Once I finished the models I moved to the machines: I had to export the file from freeCAD as an STL file which I imported in rhino and used the MeshOutline command in there to create the outlines, I also separated the inner cutouts from the outer ones in different layers, and exported them as a DXF file to import into EnRoute, which I used to create a CNC file to use on the MultiCam cutter.

I first did a couple batches of cardboard test runs to see how it worked, and doing adjustments to the slots and kerf of the pieces ( you can see the different sized slots in the pic below).

Once I was satisfied with the cardboard cutouts I used the same process to cut the pieces in MDF, but found out the spaces were a bit tight in the center joint and I had to use sandpaper to make the pieces fit, after that I went back and adjusted the model to take this tighter fit into account.

Final Piece