Stepper settings for rack and pinion

Ok i have built a plasma table and i am using the mesa 7i76 card,
i have it all working to a degree except i am having trouble figuring out the settings for what i am running to actually have accurate travel distance on my machine's rack and pinion.

The rack and pinion is MOD 1.5 Helical and i am running a 3:1 reduction from the steppers to the pinion gear
The stepper drivers are set at 1600

I have tried unchecking the microstep multiplication factor and just using the worm turn ratio but then the steppers slow down a lot and i would have to put the acceleration and velocity up crazy high to make the motors move at a reasonable speed. as seen in the pictures. any guidance would be greatly appreciated. Thanks

I never use stepconf or pncconf so here goes

Pinion travel = 20t x 1.5mod * pi = 94.247778 mm/pinion rev
3:1 gearing = 94.247778 / 3 = 31.4159265359 mm per motor revolution
1600 step / rev
steps per mm = 1600 / 31.4159265359 = 50.9295817894 steps per mm

So just save your setup to create your ini file and rewrite it so for that joint,
STEP_SCALE = 50.9295817894

Thanks for the reply i changed the step scale to what you said and moved the machine 500mm and came up at 530mm, should i just keep adjusting the step scale slightly until its correct or am i missing something still? cheers

luftlupus wrote:

Thanks for the reply i changed the step scale to what you said and moved the machine 500mm and came up at 530mm, should i just keep adjusting the step scale slightly until its correct or am i missing something still? cheers

Yes you can. But you can also work out the percentage it is out by and change the scale by the same percentage


edit : 530-500 = 30 30/500*100 = 6%

nice i didn't think of that ill try that tomorrow cheers

luftlupus wrote:

Thanks for the reply i changed the step scale to what you said and moved the machine 500mm and came up at 530mm, should i just keep adjusting the step scale slightly until its correct or am i missing something still? cheers

Funny you say that. I had one axis where the maths gave perfect results but on the other it took a lot of trial and error to dial it in the way Clive suggested.