steps per degree: accumulating error on 4th axis

[agent-r]

Hi there,

I recognised a problem when using my 4th, rotational A-axis: I did some jobs with quite a lot of rotations (spiral milling) and recognised, that after some hundreds or even thousands of revolutions, the top face of my workpiece was turned at some degrees. I initially suspected missing steps, but since i changed for a closed-loop stepper on the A-axis recently, this was rather unlikely.

The following seems to be the problem: My axis has a 6:1 gear leading to a odd steps/degree value of 53 1/3. If i read the docs of grblHAL right, the steps/degree setting is stored as a float datatype (with about 7 decimal digits?). But in ioSender 3 decimal places (=53.333) is the most accurate value i can enter. This leads to an error of 0.12 steps per degree => 1 degree per about 444 revolutions of the axis. This machtes quite exactly with the error i see on my machine.

Is there any way to set more precise values for steps/degree settings? Am I doing something wrong? Are there any (good ;-) ) reasons for the limitation to 3 decimal places? Any workarounds? Could this be improved in future releases of ioSender?

Thanks! P