Cutting Sheet Aluminum on the CNC

Advice on bits, cut directions, and lubricating coolant for machining aluminum. September 28, 2009

I'm trying to cut sheets of aluminum that are .025" thickness. I've been cutting in a counterclockwise direction with the spindle going clockwise. I believe that is called conventional cutting. Is the other way, climb cut, better? My speeds are 18000rpm and 60-70 ipm. Using no coolant. It comes out pretty good on the edge, but I was curious if there is a better way to cut this.

Forum Responses
(CNC Forum)
From contributor S:
Down cut or up cut? I use 40-50ipm with a downcut bit. This works best when you route a channel in the spoilboard first so the shavings have somewhere to go. Also helps to hold down the small parts.

From the original questioner:
I use a 1/16" upcut, and I noticed that I need to penetrate about 1/16 into the spoilboard or the tool flexes slightly and burs the edge.

From contributor S:
Wow, I misread your post as saying1/4", when it's actually less than 1/32". You could almost cut that with any bit. You could also speed up the feed with a larger bit. My material is 1/8" thick.

From the original questioner:
Okay, but how do you cut your part? Clockwise or counterclockwise around it?

From contributor S:
I generally get a good cut going either direction. Conventional cutting is the way I do it, but I noticed on the other side of the bit (on the fall-off piece), still has a nice finish.

From contributor O:
I machine a lot of aluminum composite material which isn't too different although maybe softer. Conventional cut with a 1/4" upcut single 'O' flute works very well for me. I suggest the bit would probably be more critical than the direction. You could also try a light lubricant such as WD40.

From contributor D:
The tooling folks often tell me you get better life with a conventional cut.

From contributor B:
Routing in a counter-clockwise arc with a clockwise-rotating bit is climb cutting on the outside of the bit (larger arc) and conventional cutting on the inside (closest to the axis of the arc). Make sense?

From contributor K:
I have been cutting aluminum for about 10 years and the best I have found was a 2 flute up spiral TIN coated endmill anywhere from 1/8" to 3/4". The main thing I found was, just like cutting any type of metal, it must be cool. You almost have to use some type of lubricant. There are all kinds of cutting fluids on the market just for this. That's the most important thing with cutting any type of material - wood, foam, aluminum, acrylic, and so on. I have even cut 3034 24 gauge S/S on a router. Longer tool life and better cut. Keep it cool. The other thing I had found out cutting aluminum was the type. The harder, the better. Try to stick with a 5052 or better. Anything softer will be a little harder to cut, and it will gum up the bit. I have been cutting 2 sheets of 1/4" 5052 stacked with a 1/4" 2 flute, with lubricant, cutting about 150 inches a minute at 20,000 rpm and I am getting a glass finish. I also cut 5 sheets of .050 stacked the same way with the same finish. Keep it cool and clean.

From the original questioner:
I'm cutting .025" aluminum using a 1/16 upcut one flute. What would you recommend? I have to cut with that diameter tool.