11 March 2010 update:

One note about cutting metal on the shopbot: I'm always careful to empty the dust collector before I start cutting. Don't want hot metal shavings flying into a cloud of wood dust!

Wow, cutting fluid really makes a difference. Today I cut some 1/4" 6-series aluminum plate with a 1/4" 2-flute carbide end mill. After each pass, I'd raise the head, vacuum out the chips and put a little stream of A-9 Aluminum Cutting Fluid all along the groove.

Here's what I got away with:

- 1/4" 2-flute carbide end mill (short bit -- I think it's a 1.25" flute length bit)

- 6000RPM

- 0.3 IPS (so 0.0015" chip load per flute)

- 0.060" depth of cut per pass

I found it helpful to do a dry pass to start at 0.010" depth, to outline where the groove would be and leave me a little channel for fluid for the first pass. It also showed me that my workpiece wasn't very flat with respect to the tool... :/

This chart proved handy. On some of my earlier runs, I was really pushing the recommended chip load limits.

(9 July update with more numbers)

I got some new, shorter end mills. The 1/4" 3-flute didn't sound great at the settings I liked before, so I turned down the depth-of-cut to 0.010 again (yargh):

UPDATE: ignore this set of numbers; after getting 0.050 or so into the material, the mills kept loading up. Sigh, back to the conservative numbers.

3-flute solid carbide end mill

10,000 rpm

1 ips

0.010" depth of cut

okay, a little whiny

4-flute solid carbide end mill

10,000 rpm

1 ips = 0.0015" chip load

0.010" depth of cut

very nice

4-flute solid carbide end mill

10,000 rpm

1 ips

0.020" depth of cut

not bad

4-flute solid carbide end mill

10,000 rpm

1 ips

0.030" depth of cut

a little whiny but not bad; eventually loaded up badly

4-flute solid carbide end mill

10,000 rpm

0.3 ips

0.030" depth of cut

much whinier, at 1/3 the feed rate!

4-flute solid carbide end mill

10,000 rpm

1 ips

0.050" depth of cut

whiny, then loaded up with material

4-flute solid carbide end mill

10,000 rpm

1 ips

0.020" depth of cut

this seems to be sustainable, but keep an eye on it

(Updated to fix ipm numbers)

We have a Shopbot PRS Alpha with a 2HP HSD spindle at work, and I've been experimenting with cutting aluminum on it. Here are my latest results:

All were short passes across the face of a 1/2" 6061 T6 aluminum plate (so watch for heat buildup for actual tasks). Note that the 6-series behaves MUCH differently from 5-series aluminum. I need to experiment more, but I think 5052 will be much better to mill on a shopbot than 6061.

Summary of max feed rates I felt comfortable with:

3-flute 1/4" solid carbide end mill:

6000 rpm

0.020" depth of cut

0.30 ips = 18 ipm = 0.001" per flute

1-flute onsrud spiral 1/4" cutter, 1.25" cut length.

I think I bought too long a bit so it chatters:

AVOID

1.25" 2-edge face cutter:

3000 rpm

0.005" depth

0.1 ips = 6 ipm = 0.001" per flute

2-flute 1/2" TiCN-coated solid carbide end mill:

12000 rpm

0.03" depth of cut

0.40 ips = 24 ipm = 0.001" per flute

Details:

3-flute 1/4" solid carbide end mill

3000 rpm

0.020" depth of cut

0.050 ips = 3 ipm = 0.000333" per flute

works good

3000 rpm

0.040" depth of cut

0.050 ips = 3 ipm

sounds bad; I think it's loading up

6000 rpm

0.020" depth of cut

0.10 ips = 6 ipm

seems okay

6000 rpm

0.020" depth of cut

0.20 ips = 12 ipm = 0.000666" per flute

seems okay

6000 rpm

0.020" depth of cut

0.30 ips = 18 ipm = 0.001" per flute

also okay

6000 rpm

0.020" depth of cut

0.30 ips = 18 ipm = 0.001" per flute

also okay

12000 rpm

0.020" depth of cut

0.60 ips = 36 ipm = 0.001" per flute

some vibration, maybe okay

18000 rpm

0.020" depth of cut

0.90 ips = 54 ipm = 0.001" per flute

tends to screech. do I smell something burning?

1-flute onsrud spiral 1/4" cutter, 1.25" cut length:

3000 rpm

0.020" depth of cut

0.050 ips = 3 ipm = 0.001" per flute

screechy chatter

6000 rpm

0.020" depth of cut

0.050 ips = 3 ipm = 0.0005" per flute

chatter twice as loud

12000 rpm

0.020" depth of cut

0.050 ips = 3 ipm = 0.00025" per flute

now sounds like "bizzity bizzity bizzity..."

18000 rpm

0.020" depth of cut

0.050 ips = 3 ipm = 0.000?" per flute

same but faster

12000 rpm

0.010" depth of cut

0.050 ips = 3 ipm = 0.00025" per flute

same but higher pitched

1.25" 2-edge face cutter:

3000 rpm

0.005" depth

0.05 ips = 3 ipm = 0.0005" per flute

not bad

3000 rpm

0.005" depth

0.1 ips = 6 ipm = 0.001" per flute

not bad. nice rainbow finish!

3000 rpm

0.010" depth

0.1 ips = 6 ipm = 0.001" per flute

some chatter but not bad.

6000 rpm

0.010" depth

0.2 ips = 12 ipm = 0.001" per flute

bigger c-shaped chips. occasional grindy noises

2-flute 1/2" tin-coated solid carbide end mill:

3000 rpm

0.020" depth of cut

0.050 ips = 3 ipm = 0.0005" per flute

quiet but unhappy screeches

6000 rpm

0.010" depth of cut

0.050 ips = 3 ipm = 0.00025" per flute

seems pretty happy

6000 rpm

0.010" depth of cut

0.10 ips = 6 ipm = 0.0005" per flute

starting to have some vibration

6000 rpm

0.010" depth of cut

0.20 ips = 12 ipm = 0.001" per flute

not bad

12000 rpm

0.010" depth of cut

0.40 ips = 24 ipm = 0.001" per flute

not bad

12000 rpm

0.015" depth of cut

0.40 ips = 24 ipm = 0.001" per flute

still not too bad

12000 rpm

0.03" depth of cut

0.40 ips = 24 ipm = 0.001" per flute

still okay

12000 rpm

0.05" depth of cut

0.40 ips = 24 ipm = 0.001" per flute

tends to whistle and vibrate