Speed Tuning, how to lower speed?

I'm using Repetier Firmware on Arduino Mega+Ramps 1.4 with CoreXY for laser engraver. 
Because of low laser power I need low velocity for my X/Y axis to engrave. I've got some questions:

1)How to change the normal speed for x/y axis? I can set different homing speed and maximum speed in configuration tool. What should I change to set different 'normal speed'? Now, the normal speed (M220 S100) is around 77.5mm/s (during G1/G2 moves)

2)I use M220 Sxx command to multiply my normal speed. It works well down to M220 S25. Below 25% of normal velocity nothing changes - it is always interpreted as 25%. For example, I send M220 S10 in a terminal and I receive the message "Speed multiply: 25" (the same message as if I set M220 S25). Why not "Speed multiply:10"? Why does speed multiply not work below 25%? 

3)The last thing is something I don't understand at all. I read that Feedrate as a parameter in G1/G2 moves is not supported in Repetier firmware (for example G1 X20 F100). In fact, speed doesn't change between G1 X25 F1 and G1 X25 F100 but ... It is much slower than G1 X25 without feedrate parameter. I've done some tests and this 'feedrate speed' is 7mm/s. Where does this speed change come from?

Summary: I need low velocity in my machine. The lowest I can reach with M220 tuning is ~19,4mm/s (M220 S25) and also - 'feedrate speed', which is 7mm/s. I'm very interested in forcing my X/Y axis to travel to a 7-19mm/s extent. I'm glad to get to know any solution for this issue.


  • 1) There is no "normal" speed. G0/G1 have a F parameter that sets speed. So speed is what you tell firmware to move at.
    2) M220 is meant to adjust for a gcode that normally uses correct speed. But when you see you get extrusion problems or want a print finished faster you can modify the speed set with F parameter.

    3) Not true. We support F and if you omit it it is the last one used. 
  • Thank You Repetier very much for your quick response. Now I know understand it much better. 
    My mistake was I tested low values of feedrate (F25, F50), which is a very low speed. Today I tried higher feedrates (F720 = 720mm/min = 12mm/s, by default feedrate unit is mm/min) and everything is correct.

    It seems that 7mm/s is my 'minimal speed', because no matter if I set F1, F25, F100, until F420 (420 mm/min=7mm/s) the speed is always the same. 

    Would you tell me if it is possible to change that minimal speed?
  • I already did. Reducing acceleration for the axis reduces minimum speed possible.
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