Belts Calibration

Does anyone have a tried and true method of calibrating the x and y axis belts. Circles are not coming out round.


The best way (IMO) is to use math.

Figure out how far the laser head travels with one turn of the motor. You will need to know the pitch of the belt, and the number of teeth on the pulleys.

Then you need to know what level of micro stepping the stepper driver is using.

An example;

5mm belt pitch
15 tooth pulley on motor which goes to a 30 tooth pulley. The 30 tooth pulley is attached to another 15 tooth pulley which drives the belt that moves the laser head.

So it takes two turns of the motor to rotate the drive pulley one time.
15 teeth * 5mm = 75mm belt travel for one turn of the drive pulley, or 37.5mm belt travel for each turn of the motor.

A typical stepper requires 200 full steps to make one rotation.

If you are using 1/8 micro stepping then it will take 1,600 steps to rotate the motor one time.

37.5mm / 1,600 steps = 0.0234375 mm per step (or) 42.67 steps per mm.

RDWorks has a feature where you cut a square, measure it, then input the measurements and it will tell you what the step length should be. This is not a good solution in my opinion because it will only be accurate for that one size of part that you use to calibrate. The reason is that it does not take kerf losses into account. If you use the math method then it will be accurate for all sizes of parts. Any imperfections will be the result of kerf, material movement or other mechanical reasons, but not the step length.

I should have been more clear. I have the correct steps and driver settings. I’ve been diagnosing (chasing) a bad stepper issue and now that the belts are loose I was going tight everything up but can’t get the circles nice and round. They come out pear shaped. So I was wondering if anyone used a mechanical method to dial in the belts.

Other than proper tensioning I cannot think of any other way to “dial in” the belts.

By “pear shaped” do you mean “elliptical”? If you are actually getting a pear shape when trying to cut a circle then that would be an interesting problem. Can you post a picture?

check these out

Something is probably loose. Could be a mirror, lens tube, lens holder, pulley, motor, even the laser tube. I would go around and make sure that nothing can wriggle.

Was the paper at a slight angle in the machine? The start point of most of my circles is at one of the four cardinal points, yours seems to be about ten degrees off.

Do you get better circles when running at a slow speed?