Computer-Controlled Machining¶
As part of our weekly group assignment, we wanted to test feed rate, spindle speed, and fixation options as well as the alignment capabilities of our CNC machine (EAS CNC Machine).
Calibration¶
Before any tests could be carried out, the CNC had to be calibrated. In this case, the main focus was adjusting the Z-axis height due to a new work surface. The milling head must cut lightly into the underlying board to ensure that the object is fully milled and no thin layer remains.
To calibrate, the milling head was slightly lowered into the material, the current height was read, and it was set as the new Z-zero point in the integrated CNC software.
Spindle Speed and Feed Rate¶
To test spindle speed and feed rate, we created a test file in Fusion 360, which was used to mill three different settings for each parameter. We tested both default settings and custom-adjusted settings.
The table below summarizes the different settings:
| Setting | Feed Rate | Spindle Speed |
|---|---|---|
| T1 | Default | Default |
| T2 | +25% | Default |
| T3 | -25% | Default |
| P1 | Default | Default |
| P2 | +25% | Default |
| P3 | Default | +10% |
| H1 | Default | Default |
| H2 | +25% | Default |
| H3 | Default | +10% |
| R1 | Default | +10% |
| R2 | Default | -10% |
The same tool was used for all milling operations. Only the settings were adjusted by assigning the same tool slot different spindle speeds and feed rates.
Before starting, especially with unknown results and untested parameters, we reviewed the CNC safety instructions and took note of emergency stops and fire extinguisher locations. Then the milling operation was started.
The results were initially acceptable in all cases; no operation went catastrophically wrong. On closer inspection, however, the default settings produced the best results, with the fewest burn marks and the cleanest edges.
Fixation¶
The CNC machine mainly uses a vacuum system to hold boards in place during milling. For safety reasons, however, we had an additional plate in the lab between the milling head and the bed, which can interfere with the vacuum—especially for smaller boards.
As a workaround, we fixed the board to the larger plate on the bed using screws. This requires extra caution, as the screws must not be hit by the milling head.
In addition to these measures, there is another method to secure milled parts and prevent them from shifting, which could cause damage. This is done using tabs, small bridges added in the milling settings that keep cut-out pieces connected. After milling, the tabs must be carefully removed with a chisel, but they are essential for safe handling of the parts.
