Learning about milling
Since joining the Nottingham Hackspace I've been increasing interesting in learning a bit more about metal working and machining. In particular, I've been really wanting to learn more about milling. Turning is next though! Milling has always seemed very intimidating - likely for good reason. Fast, often brittle (but strong) things spinning quickly, smashing into other things, making tiny chips of hot metal fly towards you…
Anyway, I've been reading a great book (recommended by Ben Krasnow, either in a comment somewhere or in a video) called Building Scientific Apparatus. While it doesn't go into huge detail about machining, it gives a good overview, which hopefully provides enough confidence to give it a try. I think for me, this was the case. I learnt about different types of milling tools, feed rates, clip load, the number of flutes, RPM and how all these link together. I think generally (keep in mind, I'm a beginner) the slower your spindle, the higher your feed rate needs to be. This seems counter intuitive, but it's about keeping a consistent chip size, and the chips are what carry the heat away from the part and tool.
I bought a few milling tools from Rennie Tools and APT. Two single flute end mills, at 4 and 6mm, a centre drill and some drills at 3.3mm and 4.2mm (for machine screw threads). Jelly at the hackspace kindly also gave me a few end mills of different sizes (thanks!).
I found an old aluminium heatsink which seemed like a good victim for some experimentation. I started with a 4 flute end mill (one of the ones from Jelly) and conventionally milled the side of the heatsink. The surface finish ended up being pretty rough. I think I was struggling to keep the feedrate high enough given the higher number of flutes.
Next I switched to one of my drills so I could give tapping a go. This went very smoothly and I didn't break the tap.
Then I decided to try an end mill again. I switched to one of my DLC coated single flute mills (4mm if I remember correctly) and gave it another go. The surface finish was so much better! I will stick to single flutes for manual milling I think. If I start using the CNC machine, I will try multi-fluted end mills again, but not for now!