I have seen from another post that feedrate upper limit is 80ipm for nomad.
could someone tell me what is the lower limit of it? I tried on my machine , found any F<5 gcode give the same plunge feedrate around 5ipm
Should be able to go ridiculously slow. Grbl might have a lower limit based on the way the motion planner works, but it can definitely handle 1ipm since I’ve done that and watched paint dry as it descended from the top of the machine.
Unless you switched modes, the gcode F is in mm/min. If you use G1 to move, Grbl will give an error if the feedrate is undefined or was interpreted as 0.
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Are you measuring your federate? I think you should get down less than 10mm/min. It depends on your steps/mm… What are the $$ values for your Nomad?
In teh interest of getting firm data, I spent the time (and an adult beverage) to test this out. I am running GRBL 0.9 (I have no need to upgrade to 1.x yet, so I haven’t), so current machines may differ.
The cut is a circle, 20mm diamneter using the trace tool in fusion360 (follow the line). The path length is 63mm (about).
The speeds run were 20mm/min, 10mm/min, 5mm/min, 2mm/min, and 0.5mm/min, and I checked the g-code to insure that the proper speeds were in the code.
The results:
20mm/min: actual: 3:01, expected 3:08
10mm/min: actual: 5:58, expected 6:16
5mm/min: actual 6:13, expected: 12:32
2mm/min: actual: 6:13, expected: 31:24
0.5mm/min: same again
It would appear that a) the minimum rate (x-y) is about 10mm/min, and b) that the timebase on the control is within a few percent of correct. I did not test z axis, but would presume it to be the same.
At this speed, the resolution of the steppers is a factor (about 5 step/sec), so going slower isn’t likely to do much good, anyway. This is well below where the motion can be considered continuous at the tool speeds the machine supports.
edit: see https://github.com/gnea/grbl/issues/169 re: low3st step rate of about 4 steps/sec
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Hi enl_public:
Thank you for your patient test!
I have similar number! The minimum feedrate is about 10mm/min. My test was on z-axis.
Again, it has to do with the steps per second. Default Grbl can’t handle lower than around 30 step/second due to timer limitations. Assuming a minimum of 31 step/second (not sure the exact), with a steps per mm of 200, you’re looking at a minimum feedrate of 9.3mm/min. That’s seems pretty much right on with @enl_public’s data.
EDIT: Not sure where else I’ve seen the 30step/second, but here’s a source:
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