Week 7:
Computer-controlled Machining

Mission objectives:

Make something big (on a CNC machine).

Explain how you made your files for machining (2D or 3D).

Show how you made something BIG (setting up the machine, using fixings, testing joints, adjusting feeds and speeds, depth of cut etc).

Describe problems and how you fixed them.

Include your design files and ״hero shot״ photos of final object.

At this week I studied a lot about my workflow. Mostly about how unplanned is it.
Constant route for the right steps order of machinery file making does not exists yet and my way is still very messy.
That made me ask questions about the time that I waste by correcting files when I switch from one software to another. Here I found the weakest point in my work chain.

Lately, at this course, I started to explore Fusion 360 and found it pretty expectable for many of the objectives that we need reach in our missions. Till now i’ve beed using it mostly for 3D design, which is easer for me. But yet, I’m just a novice user of it and still not familiar with very basic of its 2D possibilities. That is why I still stick with old/free/simple/unreliable software like Inscape for 2D realignment and for file format converting.

At the end of the week I figured out that it could be easer to create in Fusion 360 special sketch file for each project that need to be machined from flat sheet, especially for DXF export. It has to be single sketch that include all the parts of the design and they have to be aligned/flattened at the same plane. This way I could deliver the same geometry that I had planed in one file to the machine software, without extra copying, pasting, aligning scaling that need to be done during software shifting.

While spotting my work going through the machining I caught some small defects. One of those defects was 1.5 mm gap in few of the final model joints that had been caused by geometrical mistake I’ve made in one hole (replicated in 4 places from 30 joint elements) during the planning.

Some other mistakes happened because small double lines and dots in final file that I did not see/correct during all the process, until the job was already done. There were some clues on the way that I could analyze and understand only thanks to the decent documentation that we need to make.

Even when I made the laser cut small test, 1:6 scale, those little gaps weren’t visible in 3.5 mm thickness plywood. One of the clues for mistakes presence came when I saw ,during the laser cutting process, some dots/sparks in the machine path at the place were the dog bones holes should be placed.

The laser test parts when out fine and I did not see any problems in the assembling process at such a small scale.

The second clue came at the GUI of the Alphacam Ultimate Router CNC software. During the file check and milling steps setup I spotted and erased few small dots/lines. They looked like unplanned drill points in the middle of part that was waste and meant to stay with the board. So, I wasn't worried: it did not happened on one of the parts that I needed to cut out and I proceeded on. At this point I supposed to double check my file.

The milling lasted for 1 hour and 20 minutes. Totally used size of material area was 1200 mm / 1800 mm.

During the CNC test joint milling everything worked great and there was no gaps. The lock worked perfect - the thickness of plywood was a bit wider than 18 mm (about 18.3 - 18.5 mm) and it created decent pressure in 18 mm holes. It was impossible to disconnect the joint without using tools/rubber hammer and plenty of power.

I used 1/4 inch flat milling bit. The job had been custed in 4 passes and the last 5th pass was the finish cut with tabs that kept the parts from flying away from the board.

Another clue of damaged file was the extra dog bone ears that machine drilled and it did not look familiar for me as planed path or layer. It looked like extra drilling hole on few of the dog bones holes. Instead of getting one minimal corner arc of 7 mm diameter I’ve got there two symmetric arcs (like Mickey Mouse ears:) on the dog bone “corners”.
All of the dog bone arcs have been milled normally with the process of the passes as part of the milling path, that is why the extra drilling inside dog bone, that took place after 5 milling passes, had looked for me as unplaned work layer.