Spindle Stalling

I have been slowly working up to more aggressive speeds & feeds in 6061-T6 and I’ve been unable to exceed what FSWizard calcuates as a 1HP cut. As an example:

0.5" flat end mill
5 flutes
37 degree helix
1.125 ADoC
8,000 RPM
99.9 IPM
7.5% / 0.0375" RDoC

FSWizard calculates this as:

1.09 HP
0.71 ft-lb
MRR 4.5 in^3/min

Per MR-1 CNC Gantry Mill | Langmuir Systems this should be ~32% of spindle capacity by both HP and torque at 8,000 RPM. I tried reducing the spindle speed all the way down to 4,500 RPM with no discernible difference in the stall behavior. With these cutting parameters, the spindle will stall after a few inches of cutting. Backing the RDoC down to 5% of tool diameter is vastly more reliable.

By “stall” I mean that the spindle stops completely and the spindle breaker must be switched off anywhere from seconds to minutes in order to bring it back to life. Also, as the MR-1 controller has no feedback from the spindle driver or encoder, the machine continues to try to feed into the stock… where the best case is that the steppers start to skip.

Which leads me to a couple of questions for the community:

  1. Has anyone be been able to achieve an MRR > 4 or a cut >= 1HP in 6061 or similar soft alloys?

  2. Has anyone else seen this stall behavior where the only way to recover is to the remove power from the spindle servo driver?

I haven’t tried programs that aggressive.

The spindle is a servo. If it can’t maintain the intended position without some error value it would go into alarm and will require a power reset.

The control isn’t wired up to the spindle alarm signal, so it doesn’t know to stop the axises.

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I did stall the spindle when I had chip welding from insufficient cooling and my workpiece welded itself to the cutter. I had to do the power reset.

Proper chip evacuation is possibly your limiting factor with that tool in the MR1. I would think pushing a 5 flute tool to that MRR would need some serious coolant pressure and coverage in order to keep the relatively small flutes from filling and recutting your chips. What does the cut, chips and tool look like after the stall?

Speaking of, I have tested the stall functionality here as well… I took a 4F .5" end mill and tried an impromptu rapid plunge cut into the rear of one of my Langmuir vise early on. I never calculated the MRR, but it was too much for the MR1 :joy:

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This was with an IPT of .0025, which is considered a finishing chip load. See

The chips are the normal long chips from a finisher. The tool is completely fine with no welding.

I don’t understand how Langmuir was able to achieve the claimed MRR of 18 in aluminum. It appears that this spindle is unable to achieve 1/3rd of the spec.

I’ve stalled the spindle one time so far. It was around 300rpm with a 1.25" woodruff cutter feeding at .0003" per tooth on 416 stainless.
The spindle stopped, machine kept feeding and resulted in me needing to tram the spindle.
Most of the milling my MR1 has done was on either 316 or 416 stainless, so I haven’t gotten to stretch its legs on aluminum aside from some fixturing. That was all machined at the speed, feed, depth and step over on the chart Langmuir has listed. If I get to do some more aggressive milling on aluminum I’ll see what I can get out of it.

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Maybe of some help. At least it was for a relative newbie like myself.
Cutting aluminum with a CNC Router

Cutting Aluminum with a CNC Router Part 2


Two awesome videos. Expert explanation.
I never try to stress out my machine and most of my projects are not time of the essence.


I would try achieving that rating with a 2 or 3 flute

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The only difference would be the harmonics from having fewer flutes in contact. I have tried 1/2" 2 flute 2" LOC mills. The mr-1 isn’t rigid enough for “fast” cuts with only a fraction of a single flute in contact without chattering. The total power required for the cut would be the same.

I wouldn’t expect to obtain the full rated power of the spindle. The speed doubler is going to loose half the torque but the limit being less than 1/3 of the published specifications is a surprise.

Id give it a shot before you knock it 8-12 should be achievable per calculator. 2" LOC is pretty long. id try some 1" LOC and load it up radially. Looks like 1" DOC and .080 would be around 8 MRR