What's new
What's new

Adjusting feeds and speeds for low power machine

___brad___

Plastic
Joined
Aug 24, 2022
Location
San Francisco
I'm roughing 6061 and getting a nice finish. The machine doesn't sound good though. It's low-power ( <2 HP). I'm guessing the sound is from the machine struggling.

How do I adjust my feeds and speeds to compensate for the low power (assuming that is the problem)? Decrease the feed? Decrease step-over?

ADOC: 0.75"
RDOC: 15% dia
Feed: 24 IPM
RPM: 4000
Chip Load: 0.002 IPT

I'm using a 3/8" dia roughing mill with chip breakers. It has a 1" LOC.

Here's a video:
 
Last edited:
I can't hear it on my computer, (bad speakers) but to start I would choke up as far as possible on the shank of the tool. You have a lot of excess sticking out.

Those numbers are already conservative, even if the tool is HSS. If that is carbide, you might want to switch to HSS. Low power low rigidity machines have trouble with carbide. The stiffness of the tool is able to overcome the rigidity of the machine. You could also check your runout at the tool tip.

If you're already using HSS you might try a shallower depth. I think overly deep cuts are harder for light machines to handle then overly wide ones. Been so long since I ran one, but I'm thinkin that's what I found out way back when.

BTW... if the sound in the video is simply the motor bogging down, then either find a better section of your torque/power curve, or again, a little less DOC.
 
Last edited:
Is that a name brand end mill or amazon/ebay special? You have plenty power for those speeds, not rigidity.
Helical Solutions end mill.

Re: rigidity -- yeah, that makes sense. I'm using a large chunk of aluminum on a small vise. And the side of the stock facing the adjustable jaw on the vise is held in place with a brass rod.

Thanks!
 
On a low rigidity machine / setup, I find it's best to increase RPM while decreasing feed and stepover. That cutter would be happy in aluminum at 20,000+RPM. Is 4k your max? Minimizing stickout and holder length is critical.
 
sounds to me like the tool in the video is a bit slow in the rpms, or the tool is just dull. sound is like it is heavy loaded or the torque is high on the motor, all depends on the torque curve of the machine you are using for your settings.
quick calculaton is saying 400SFM, which is half of where it should be.
IPT is a bit low, i like to be around 3IPT and about 0.100 step over or about 30% and about 8000 rpms
 
Last edited:
On a low rigidity machine / setup, I find it's best to increase RPM while decreasing feed and stepover. That cutter would be happy in aluminum at 20,000+RPM. Is 4k your max? Minimizing stickout and holder length is critical.
Unfortunately the max is ~5.3k.

Thanks!
 
sounds to me like the tool in the video is a bit slow in the rpms, or the tool is just dull. sound is like it is heavy loaded or the torque is high on the motor, all depends on the torque curve of the machine you are using for your settings.
quick calculaton is saying 400SFM, which is half of where it should be.
IPT is a bit low, i like to be around 3IPT and about 0.100 step over or about 30% and about 8000 rpms
"torque curve"... Interesting. Never heard of it until now. I'll look into making one. Any recommendations on a tachometer?
 
Generally if you don't have enough power and the motor is starting to bog down, you don't decrease the feed rate, but you decrease the depth/width of cut.
Also as someone mentioned, depending on your spindle type you will have maximum power available at a certain RPM range. If it's a VFD, it would usually be up around 85% of the max motor RPM
 








 
Back
Top