Rotary Calibration Math

Red and White K40


Firmware: _Smoothie
Have the FTG K40 Rotary, everything mostly works exactly as expected

Went to draw a 25mm^2 square and width was correct but the height was 70mm’s

I searched around, but calibration steps expect a complete rotation, I’m not sure what that means, smoothie tho asks for steps per mm, the stock cohesion firmware had A axis set at 157.5, I seen on the forums that the cohesion rotary is set at 17.77

I’m using lightburn, I have the wheels on my rotary set and the diameter of the workpiece set.

The 17.77 is still 10mm off.

What I’m really asking is, what is the math to calibrate it on my own? Like I said earlier, the formulas I found were expecting complete revolutions (and big numbers)


It would be better if the rotary manufacturer could provide you the actual steps per mm value for the rotary that they sell.

The “formula” is a simple proportion - send a command G0 A360 F600 which should turn 1 revolution, and observe how much it actually turns. Then adjust the steps per mm value accordingly.

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