My last major aluminium part to be cut out was the lens surround, which is twisted to active the camera. In the models I am presenting for my degree, one will twist for demonstration purposes and the other will remain fixed. With a component height of roughly 21mm, I had to invest in some heafty aluminium blanks to cut them out from. I ended up with 3 90x90 1inch (26 ish mm) blanks to match the massive 1 inch block which the outer rim was cut out of. The 90x90 footprint meant that they could be drilled and pinned to the existing jig which was used to hold the block in place when milling the control dials.
I was fairly anxious about machining these parts due to their depth and complexity. I ended up spending an entire day machining the first one, setting up the jig in XY Zero and perfectly aligned along the same axis as the pins, and setting up tools and cutting paths which could be saved and run in batch on the following parts.
The cutting required 3 different milling tools in the end. A 12mm end mill hollowed out the centre rapidly, whilst a 6mm end mill handled all the facing and Z-Level roughing to within 0.2mm of the final surface (excluding areas where the rad of the tool was far to big). Then a 3mm ball mill went in and completed the Z-Level finishing, getting into all the tight rads while smoothing out as much of the surface as possible. The finishing pass operated at a mighty small 0.1mm Z step (shown below).
Above we can see the 3mm ball mill cutter used for the finishing pass. One of the trouble I encountered was that the spindle was on a collision path with the top face of the aluminium blank when cutting with a conventional cutter. To avoid this, I found a cutter which had had its shank ground down to give the tip greater reach, just enough to prevent a spindle collision which could really have damaged the part.
The final parts were good, but annoyingly a software error caused an annoying ring to be left around the entire part. The line is where the cutting tool has skipped about 0.4mm of Z level steps. The resulting line is therefor upto 0.2mm max larger than it should be. While this may seem minute, it very obviously has a visual effect. This line was reduced when for the second and third part copies by trying to alter the software's method of generating the cutting path, but a small 0.1 line still remains which will need to be polished out.
