rpm and feed rate for aluminum

1. Years ago, I learned RPM=CS*4/D. This you can do in your head, and it's close enough for most work. CS for 6061 aluminum should be around 250 FPM with a HSS cutter. So, RPM=250*4/0.5 or 2000.

2. Feed rate is something that you can look at any book, but it won't tell you enough. If you're using a HSS end mill, do you have a regular or high helix? If you have a regular helix end mill, you can usually get .001" per tooth with aluminum (maybe more, that's conservative). So, .001*4*2000=8 in/min. This is a starting place.

3. TIN, ALN, and other coatings are applied to cutters to extend the edges' life. There are two ways of looking at this: running the same speeds and feeds as uncoated tools and getting 10% longer tool life, or running 10% faster and maintaining the same tool life. For most home shop use, I don't think that coatings are worth the extra money.

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Thanks roninB4 for quite some insight!

So I should not worry so much about feed and spindle speed then, but rather keeping chips away. This is somewhat a problem at the moment since I don't have compressed air (another thing that I need cash for...). Now I just spray chips away with my coolant.

Is there a downside of having too little feed (or too fast spindle) other than the longer milling time? I believe I've read somewhere that if the feed is too slow, the tool will gnaw on the stock instead of actually cutting. Is this correct?

So if I understand correctly; the packing of flutes can come from two factors: 1. Too many chips not being properly evacuated; and/or 2. Too hot, which melts the aluminum to the cutter.

Thanks again for the very insightful answers. It's much appreciated!!

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