Just wondering if anyone has used downcut endmills for cutting aluminum? I was looking at some on amazon and most specify only cutting wood, plastic etc but not metal. I cut a lot of shapes out of thin aluminum sheet and was thinking about starting the cut taking one or two really shallow passes just to get things going with the down cut, then switch over to a my upcut single flute to finish the job. In theory that way I end up with a smooth finish on the top and bottom with little finishing work needed.
I have tried with a 1/8 two flute downcut carbide mill when I had a problem with reach with my 1/8 single cut upcut. The angle doesn’t produce any cutting / chip formation, just tries to deform / smear the metal. The carbide snapped after half an inch of that. If you have a HSS endmill, it might keep on grinding each other for longer without breaking, but won’t cut per say.
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Can you run a small chamfer around the edges? I try to use a 0.2mm chamfer on all my aluminum pieces to break the edge and keep it clean.
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My apologies for being such a newbie, what exactly does running a chamfer around the edges mean? I’m always looking for ways to improve my aluminum cutting 
A chamfer is a (usually) small angle cut into a sharp corner
A downcut bit is generally intended to be used for “side milling”, rather than end milling.
i.e. you would be better off cutting all the way through your thin stock rather than taking multiple shallower cuts. The downward spiral is going to push the chips downward, with the advantage of producing a much cleaner top edge, as well as delivering the force of the cut downward preventing the stock from lifting during the cut. You will end up with a burr on the bottom of the stock that can be quickly cleaned up with a piece of sandpaper or a deburring tool.
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Here’s some Aluminium with a 0.25mm 45 deg chamfer run around the top of the cutout profile.
I’d avoid a downcut endmill in a slot operation, it’s likely to just jam up and weld chips into the cutter. You might get away with running it at the sides but I’d still probably want some lubricant to stop the bottom of the cutter clogging up, especially in thin sheet Aluminium which is likely quite a soft and gummy alloy.
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