Calibration tips

[jonathanmahnken]

im running uccnc on a 5'x10' cnc router. All drives are ball screw. the z and x axis are direct drive. the y axis is ball screw with a belt and pulley system that ride along with the Gantry. I can not detect an play... The x and z have been easy to calibrate, but I am having trouble getting toward zero on the long y axis. I am swinging back and forth between too long and too short of a move(+- 3/32"). What is the best way to calibrate a long axis like this?

[charliem]

I find the calibration works best using a slow jog speed.

[jonathanmahnken]

thank you what speed would you recommend

[charliem]

I set the jog speed to around 5 in per min. After all I am looking for accuracy I'm not in a hurry.

[Battwell]

put a piece of tape on your machine against a known point at one end of travel. (against a bearing block for example)
then command your machine to move eg 2m and measure from the tape back to the reference bearing block.
then once this is correct re check at maximum distance of travel
always calibrate move distance over the longest length available.
if you measure over a short length any error is multiplied over a long length measurement.

best way is to actually calculate the steps per from motor steps per revolution divided by gearing and ballscrew travel distance per rotation.

[CL_MotoTech]

Make sure you start your calibration with already having moved the axis in the same direction as calibration.

So if I am doing Y, I zero Y and then calibrate to Y5 or something like that. Before starting the calibration I would send it to Y-.2, then Y0, and then start the calibration. This removes the backlash error from calibration distance.

Slower is definitely better, and don't be in a hurry when you do the process. It generally takes like 5 to 10 tries before I see very consistent results.

[jonathanmahnken]

Thanks!

[jonathanmahnken]

so when calibrating the long axis(y) should I go back and forth across the table, or home the machine to the back corner every time before running calibration?

[jonathanmahnken]

also what are some good starting points for my acceleration and velocity settings. Im running stepper motors with geko 201 drivers.