7. Computer controlled machining

This week we designed parts for CNC milling machine, made setups for the milling path and cut the parts.

During the group work we observed how to make the cut paths and the operation of the machine to cut certain parts, as shown by our instructors Eikka and Antti. We listened lecture on the safe operation of the CNC machine, using the safety glasses and ear protectors.

Designing structure for computer controlled milling.

I used FreeCAD to design the structures for CNC milling. I did the design in a similar way as during the computer controlled cutting and 3D scanning and printing weeks. I used part design, made a sketch and used pad tool.

Figure: Cabinet design with freecad.

I had first made a design that consisted of all parts, but when I tried to save it as a step file, FreeCAD complained that it was not possibe to save multiple bodies as step file. Therefore, I saved all the parts separately to different step files.

Figure: Designing the structure with freecad

I opened the files in Fusion360, and put the parts next to each other. All of the parts did not fit to the board, so I designed the cut path for one of them separately, so that it would be cut from a separate board.

Figure: Cut path setup using Fusion 360.

Before going to milling I realized that I had set a slightly wrong value for the width for few parts. I decided to make a quick correction by changing the width of one part. Unfortunately, it turned out that the change was not good. However, mostly the design could be assembled, I just could not use the back plate of the shelf.

From Setup - I chose origin: stock bottom, and choosed bottom left corner using mouse. x-direction towards right, y-direction (longer direction of the board on cnc machine) up.

From Stock - Stock top offset 0 mm, Stock Top Offset 0 mm, Stock Bottom Offset 0 mm.

Figure: Setting the origin in left bottom corner, with correctly aligned axes.

The tool libraries for the milling machine need to be set, so that the path can be created with the Fusion 360. I downloaded the correct library FABLAB_ROUTERI_TOOLS_9-2018.hsmlib for our CNC machine from the Fab Lab Oulu Gitlab site wiki.

After this I selected the milling head (8 mm flat head) that we would be using in the milling machine.

Figure: Selecting the milling head.

After this I proceeded to the path settings. I chose Turning 2D - 2D contour.

From tool tab - select 8 mm flat head. Geometry tab - checked tabs, tab distance 200 mm otherwise the defaults. Heights tab - top height 0 m offset, bottom heihgts 0 mm offset. Passes tab - multiple depths, even stepdowns, maximum rouhing 3 mm. Linking tab - I unchecked lead-in (entry) and lead-out (exit).

Figure: Settings for the contour.

Figure: The parts were cut in two separate boards, since they took so much space.

Then I proceeded to simulate the path using Fusion 360. I chose Actions - simulate.

Figure: Simulating the path with Fusion360.

After checking that the simulation seemed ok (four passes and leaving tabs), I created the file for the CNC machine by choosing Actions - post-process.

I imported the CNC machine settings for the post processing, FabLabCNC.cps, from Fab Lab Oulu Gitlab site wiki.

Then we proceeded to take the ready file to the CNC machine.

Using the CNC machine

Figure: The cnc machine operation desk.

Figure: Starting the software Ncstudio

Figure: The machine prompts to move the axes to the mechanical origin.

Figure: The vacuum pumps are controlled by levers and they were turned on before the calibtation.

Then we proceeded to calibrate the origin by choosing Operation - Mobile Calibrator.

Then we moved the milling head to a good position for performing the calibration in z-direction.

Figure: Setting the origin in z-direction.

Figure: Setting the origin.

The head was moved to the desired origin in x- and y- directions, which was then set on the computer screen.

Figure: Selection of the origin was done by clicking the x- and y- boxes on left upper corner.

After calibration, the cut path was first simulated by clicking the small play button with screen. After checking that the path seemed to be cut correctly, the real cutting was started by clicking the large play button.

Figure: The real cutting process had been started by clicking the large play button.

Figure: Safety board was put in front of the machine.

Figure: Switches for the vacuum pump and dust collector.

Figure: Operation of the cutting.

Figure: Once finished, the vacuum pumps and the dust collector were turned off.

Figure: Tools to open the milling head to remove the cutting head.

Figure: The switch to turn off the machine.

Assembly

The part that was originally designed as back plate did not fit in to the cut design. This was because I had made a last minute correction to the design, but did not remember to change dimension of the back plate. It does not matter so much. I decided to leave the back plate away and use the cabinet in other way, so that the original back became now the front. I would use the cabinet in my final project. The Freecad file for the parts that I used in the final version and the final project are here. The corresponding svg file is here.

Figure: The parts were not directly fitting, but it was close.

Figure: The parts were not directly fitting, but it was close.

Figure: I had to use file quite much to get the parts fitting.

Figure: After removing some wood, the fit was good.

Figure: Final assembly.

Here is the design for parts that were milled. Here is the corrected desing (which was not milled).