Desktop metal milling with FreeCAD¶
Jens Dyvik treated the group with a workshop on milling metals in a Fab Lab. The original intention was to do it on the ShopBot, but the $500 Lunyee desktop milling machine turned out to be enough!
Endmills¶
Short single flute endmills work best for milling aluminum on a CNC router. When you only have one flute (one cutting surface), that leaves plenty of space to clear the chips away. And for milling hard metals, how much the endmill pokes out of the collet matters greatly in terms of vibration.
For milling steel, carbide coated four flute endmills with a small diameter do very well for high-speed machining.
Svavar brought some hard aluminum and St 235 steel for testing. He had to pay a weight penalty at the airport, but it was worth it.
Jens brought a selection of endmills, and selected 3 mm single flute endmill for the job. He then found a similar endmill from Cutwel online: E5E47
PDF with recommended cutting parameters for aluminum
The cutting data PDF was used as a reference to set the feeds and speeds in the FreeCAD CAM workbench. The fz value on the right is often the only one that the manufacturer specifies for an endmill. You take it and multiply it by the spindle speed you intend to use, to obtain a good feed rate. In this case, that results in 0.094*10800 = 1020 mm/min.
The trick to milling metals on a machine that isn't really designed for it is to use a bit with a small diameter along with a high-speed machining strategy. Fortunately, the FreeCAD CAM workbench provides adaptive clearing, which maintains constant stress on the bit. It's best to start outside the part and eat your way in with a small stepover of 8 percent in this case. Open the FreeCAD file and go over to the CAM workbench to see more details.
Quentin put his high-speed accelerometer board against the spindle as Þórarinn ramped up the speed. Then Quentin opened the recording in Audacity and measured the lowest strong frequency in the plot of the data.
Aluminum¶
This is hard aluminum from a machine shop, but we don't know which kind.
Protective equipment¶
It's always important to wear safety glasses when milling, and especially so when milling metals. There weren't enough safetty glasses for everyone who was interested in the metal milling workshop, so a piece of transparent acrylic was used instead:
Communal protective equipment
Þórarinn made another piece of improvised equipment when aluminum chips started getting into the leadscrew underneath the bed of the machine:
Þórarinn installing the paper way cover.
Steel¶
The Z height was calibrated with a piece of paper, just like on a 3D printer.
The way cover works well.
A slot successfully cut in steel 235 using FreeCAD CAM and a $500 desktop mill.