Wednesday, June 17, 2009

Shopbot aluminum feeds & speeds

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

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