GRBL with low feed rate not working I have a cheap 3000 mW laser cutter that I'm trying to cut 3 mm black acrylic. I'm lowering the feed rate to try to get it to cut in one pass.
I have the G-code for a small circle (16 mm) but it seems any feed rate below about 25 mm/min is being ignored and it uses 25 mm/min anyway. The laser cutter has been set up with GRBL 1.1h and I have checked that feed rate is being read in by GRBL correctly. If I set a feed rate of 35 mm/min, that is processed correctly - but it needs two passes to cut the acrylic.
Please see G-code below:
G90 (use absolute coordinates)
M4 S0
S0 
G0 X9.6 Y18.16
S1000 
G1 X10.98 Y18.21 F20
G1 X12.27 Y17.99
G1 X13.48 Y17.55
G1 X14.58 Y16.9
G1 X15.56 Y16.07
G1 X16.41 Y15.1
G1 X17.12 Y14
G1 X17.68 Y12.82
G1 X18.06 Y11.56
G1 X18.26 Y10.28
G1 X18.27 Y8.98
G1 X18.08 Y7.7
G1 X17.82 Y6.88
G1 X17.48 Y6.11
G1 X17.06 Y5.39
G1 X16.56 Y4.72
G1 X16 Y4.11
G1 X15.37 Y3.55
G1 X14.7 Y3.06
G1 X13.98 Y2.63
G1 X13.22 Y2.27
G1 X12.43 Y1.98
G1 X11.62 Y1.77
G1 X10.8 Y1.63
G1 X9.15 Y1.6
G1 X7.62 Y1.89
G1 X6.23 Y2.47
G1 X4.99 Y3.3
G1 X3.93 Y4.34
G1 X3.06 Y5.55
G1 X2.41 Y6.89
G1 X1.98 Y8.33
G1 X1.81 Y9.83
G1 X1.91 Y11.35
G1 X2.3 Y12.85
G1 X2.99 Y14.3
G1 X3.38 Y14.87
G1 X3.8 Y15.4
G1 X4.27 Y15.87
G1 X4.76 Y16.29
G1 X5.29 Y16.67
G1 X5.84 Y17
G1 X6.42 Y17.29
G1 X7.02 Y17.53
G1 X7.64 Y17.74
G1 X8.28 Y17.92
G1 X8.94 Y18.05
G1 X9.6 Y18.16
S0 
M5 S0
G0 X0  Y0 Z0 (move back to origin)

This G-code was produced with LaserGRBL (and modified by me, to no effect). I have tried F1, F2, F3, F4, F5, F10, and F20 and they all take the same amount of time to complete.
What can I do to perform a cut in one pass since these low feed rates appear to be ignored?
This was likely due to reaching the limitations (maybe minimum step rate) of the stepper drivers which were 4988 drivers. I updated them to 8825 drivers which were able to support a speed of F20 correctly. I have not yet tried them at lower speeds.