Menu
What's new

Cutting aluminum feed/speed/chipload question

Brent Dowell

Brent Dowell

Administrator
Staff member
Messages
16,586
Location
Reno NV
So I'm planning on using my OX cnc to cut the holes in 4"x6"x3/4" piece of aluminum. The holes will be for some M8 screws, so a little bigger than 1/4".

I was planning on using a 2 flute carbide cutter to do the cutting.

From my research on these 'shapeoko' class machines, it's suggested to use a chipload of .001 when cutting aluminum. 5-10% of bit diameter for depth of cut, and 40% stepover with an rpm of 10000.

Does this seem reasonable? I'll find some aluminum to test on before I cut my plate, but would like to get this in the ballpark.

1679955955529.png
 
I don't cut a lot of aluminum and I don't have a tool database in my Vectric tool database for aluminum. I have cut a lot of metals including aluminum in industrial machines. You cannot compare an industrial application to our hobby level machines. Industrial cutting would be .010 - .015 or so chipload.

I have cut steel on my machine at .0008 to .0012 at 3200 and 2800 RPM. My spindle, I think Carol got the same spindle, about 4hp.

Aluminum is gummy sticky stuff, you do not want to generate heat in the cutter or you will get chip welding on the cutter.
Feed too low and RPM too high will generate heat. The .001 seems a bit low. OK start there, but if you can increase chipload, go for it.
Aluminum should not be babied

DOC - ,010, Again that seems light. Generally I say half the cutter diameter for DOC. However it is machine capability dependant.
The chipload should trump the DOC

Carbide 2 flute cutter is a definate -- if you have a coated cutter that is much better, to help against chip welding. TiAln would be my choice for a coating

Keep the tool stickout as short as possible.
Stubby 2 flute cutter is best.

If the cutter is screaming - increase chipload
Also STUBBY STUBBY - keep the entire setup STUBBY

I use COOL TOOL, TAP MAGIC is OK - WD40 is ok

Aluminum extrusion is a different grade - maybe 6005 or something like that.
Sticky gummy stuff for sure

If you buy aluminum 6061-T6 is a good all around grade.
 
Good info. It's 6061 aluminum, and basically I'm just milling a few stepped holes and a few other holes.

So, basically, I should up the chipload a bit and that will be a balancing act between rpm, doc, stepover, and ipm.

I think I need to do some research on the minimum RPM the spindle will run at. Its on my old machine which is a .8kw water cooled spindle.

Thanks!
 
The balancing act will be with feedrate and RPM.

I don't know your machine, but on mine I can turn a dial for feedrate override.

If the RPM stays constant and you adjust feedrate override then you are adjusting chipload directly.
Faster feedrate means higher chipload and visa versa.

Adjusting to some exact numbers is not critical.

Do you have access to a torque curve on your spindle?
Generally the torque is at higher RPMs but the curve will show where it drops off.

Aluminum with carbide, coated is better on aluminum, can deal with high RPMs ok.
The chipload will be governed more by the feedrate, within the machines capability and rigidity.

You will need the RPM to get the needed horsepower to drive the end mill through the cut.

When cutting steel you need the lower RPM's
Your new machine will be able to do that.
RIGIDITY is key.
 
Brent your .8 KW equates to a little over 1 HP. The spindle motors are using a vector drive designed inverter to adjust the speed. Depending on the motor design it either a 2 pole or four pole motor. If it is a 2 pole motor then the "base speed is 3600 RPM and the max torque it can produce is little over 63025 inch pounds". From 0 to 3600 RPM (0-60 htz.) you are in a constant torque mode. From 0-60 Htz. the controller operate on a volts per cycle (@ 220 volts input the controller changes the voltage as well as the frequency at a rate of 3.66 volts per cycle). Your torque is constant and the horse power is dependent on speed (HP= Torque x RPM/ 63025 if the torgue is measured in inch pounds) and the speed is a function of frequency. So you Max cutting power is at 60 Htz or 3600 RPM. This is a constant for any motor. Above 60 HTZ the controller out put voltage is constant at 220 Volts and the speed is increased by changing the frequency. Toque will actually drop off as speed increases. HP remains constant. So at 120 Htz the motor is running at 7200 RPM but since it is still producing 1 HP you have 31512 in.lb. of torque. (HP = Torgue x RPM/63205). ok my physics major just came out, sorry.
 
Leo Voisine said:
The balancing act will be with feedrate and RPM.

I don't know your machine, but on mine I can turn a dial for feedrate override.

If the RPM stays constant and you adjust feedrate override then you are adjusting chipload directly.
Faster feedrate means higher chipload and visa versa.

Adjusting to some exact numbers is not critical.

Do you have access to a torque curve on your spindle?
Generally the torque is at higher RPMs but the curve will show where it drops off.

Aluminum with carbide, coated is better on aluminum, can deal with high RPMs ok.
The chipload will be governed more by the feedrate, within the machines capability and rigidity.

You will need the RPM to get the needed horsepower to drive the end mill through the cut.

When cutting steel you need the lower RPM's
Your new machine will be able to do that.
RIGIDITY is key.
Click to expand...
I'm trying to find some more info on what I have on the OX. Been a while since I used it, but I'll see what I can find. The problem is it is not a very rigid machine compared to the new one. I just need to get through this one plate with it before I retire it. I probably can come up with alternative ways to create the plate, but this seems like the most fun.


Don Baer said:
Brent your .8 KW equates to a little over 1 HP. The spindle motors are using a vector drive designed inverter to adjust the speed. Depending on the motor design it either a 2 pole or four pole motor. If it is a 2 pole motor then the "base speed is 3600 RPM and the max torque it can produce is little over 63025 inch pounds". From 0 to 3600 RPM (0-60 htz.) you are in a constant torque mode. From 0-60 Htz. the controller operate on a volts per cycle (@ 220 volts input the controller changes the voltage as well as the frequency at a rate of 3.66 volts per cycle). Your torque is constant and the horse power is dependent on speed (HP= Torque x RPM/ 63025 if the torgue is measured in inch pounds) and the speed is a function of frequency. So you Max cutting power is at 60 Htz or 3600 RPM. This is a constant for any motor. Above 60 HTZ the controller out put voltage is constant at 220 Volts and the speed is increased by changing the frequency. Toque will actually drop off as speed increases. HP remains constant. So at 120 Htz the motor is running at 7200 RPM but since it is still producing 1 HP you have 31512 in.lb. of torque. (HP = Torgue x RPM/63205). ok my physics major just came out, sorry.
Click to expand...

LOL, Greatly appreciated. I need to double check exactly what I have. Will be doing a bunch of research today, as winter has not yet left Northern Nevada. More chance of precip and temps too cold to work in the garage. I will try and digest this info.
 
Leo,
From what I can find, the minimum useable rpm is 7000rpm, with the torque getting to a max at 15000rpm, and maximum rpms is at 24000rpm. So I'll boost the rpms to 15000 and bump up the feedrate. Be nice to not wait all day for the job anyway.

Not sure how this relates to what you wrote Don? But here's what I'm using, it's 220volt VFD and 800watt water cooled spindle.

1680027661976.png
 
You must log in or register to reply here.
Top