Hi all,
Apologies if this is covered elsewhere, but I couldn’t find the answer here.
I used a Nomad 883 for many years and now I use the Nomad 3. It’s a great machine.
I used to stall my spindle fairly often on the 883. I stall it less now, but I definitely still see it drop in speed in some operations (and I nearly stalled it today).
I use a tapered reamer quite a bit. Feedrate is slow, and I am pecking.
Even still, when the tool is in full contact with the part, the spindle really struggles. I’ve tried both high and low RPM. It seems like I have the best luck when the RPM is cranked all the way up to 24krpm, but perhaps this is just inertia. I’d love to not have to run at 24krpm all the time.
Does anyone know the speed / torque curve for the Nomad 3? Barring that, can anyone just say “you get the most torque at (x)” RPM?
Let me know if I am missing something, and thanks in advance!
Since I didn’t hear back from anyone, I tried some experiments:
I used a taper pin reamer, The material was graphite.
The hole was pre-drilled to a “close” diameter.
The max contact length along the reamer was about 1.2"
I varied spindle RPM from 5krpm up to about 14krpm.
I also varied pecking depth from 0.01" to 0.001"
Finally, I varied plunge rate from about 6ipm to about 1ipm.
Almost all combinations slowed down significantly near the end of the operation and generally stalled. The last 10% of the operation was always the “stall spot”.
Peck depth seemed to make the most impact on stall likelihood (although it still stalled at 14krpm and 0.001" pecks)
Plunge rate did not change the results monotonically – IE, slow was not always better than fast.
Finally, it was not clear how much RPM mattered.
Lastly, when stalls were occurring, the internal LEDs would dim on the Nomad. I sort of wonder if a stiffer power supply would help?
If anyone else has any ideas, I am open. Otherwise, if someone else finds this thread, I hope it is helpful to you!
Inertia is definitely a factor that helps. It’s why the pulley on the Nomad 883 was made in brass.
The deeper you go, the more of that contact length you engage, so it makes sense that the last 10% is where there’s the greatest stall risk. There is no published torque curve, but subjectively, I like to run the spindle at ~80% of the max RPM.
During a stall, the motor controller wants as much current as it can get, but in our testing, a beefier power supply did not help much. It’s such a fast, transient spike in demand that either the power supplies couldn’t step in fast enough to stop the spindle from irreversibly bogging down, or maybe there’s another bottleneck in the circuit since it’s a shared power supply/rail.
How many flutes is your reamer? Is it possible to step down the flute count, since that will have a big impact on the torque needed to drive it?
Todd, Machinery’s Handbook has a discussion and chart (page 1888-1889 in the large-print 31st edition) for step-drilling pilot holes for taper pin reamers. Depending on the size, the chart calls out 2, 3 or 4 drill sizes to be used. It calls them out for straight-flute reamers, saying that with spiral-flute reamers this is not necessary (possibly because with spiral-flute reamers it is more of a shearing action).
Depending on the diameter of holes you are working with, you might be able to profile the pilot steps rather than drilling, in that case being able to make a pilot hole with more, but more finely graduated in diameter, steps.
There was a power curve in the Hsmadvisor App that somebody uploaded. I’ll see if I can screenshot it here.
What has me surprised is you guys manage to stall the motor and live to tell the tale. My machine blows the Spindle control board at the first sign of stalling.