What am I doing wrong here? My X-axis roller is 3.58" in diameter. (3.5" ABS pipe and 0.040" grip tape) That makes the circumference 11.2468922". (C=pi*d) So each revolution of the roller is 11.2xxxx inches of linear travel. The stepper motor is set to 1/8 step so that is 1600 steps per revolution. The belt reduction is 300/18 or 16.666667 motor revolutions for 1 drive roller revolution. Following that logic 1600 steps times 16.6xxx revolutions equals 26666.67 steps per drive roller revolution. Divide 26666.67 by the circumference should give me the steps per inch, right? (26666.67/11.246xx= 2371.02xxx) Why is my calibration of the X axis almost exactly half of that?

Also, now concerning the Z and Y axis; if the motor is 1600 steps per revolution and the lead screw pitch is 20 revolutions per inch the calibration should be 32000 steps per inch. My Y is off about 1/16” over 20 inches. Do you suppose there is that much error in the all thread? The Z-axis measures fine, but of course you only have 2 inches of travel to measure.

Just curious.
Dave

 

I gave up on trying to do the math, because it's only a starting point anyway. Just put something (I used a 48" straightedge) between the rollers, tell it to go 40 inches, and measure what you got. Then tell it what you got and let the software do its own calculation.
Calibrating Y is easier - just lay a straightedge along the slot.
Calibrating Z, just remember to tell it to go minus 2 inches.

Yes, there is probably that much error in 20 inches of 1/4-20 allthread, as that would be well within normal machining tolerances for thread pitch.

If the software wants to count pigknuckles-per-furlong, as long as it repeats accurately, it doesn't matter. :mrgreen:

 

This Ruler tape works well for calibrating the X Axis, Just stick it on a piece of foam at zero and see where it ends up. Attached files