Steps Per Rotation: Roller Rotary

Applies to: MIRA and NOVA with a roller rotary

This guide shows how to adjust steps per rotation (SPR) when you work with a rotary. Adjust the SPR when the dimensions set in your engraving software do not match what the machine produces.

What you need

• Computer with LightBurn
• Rotary
• Test cup or item to engrave
• Calipers or a cloth tape measure (mm)
• Calculator

What are steps per rotation?

Steps per rotation is the number of steps a stepper motor needs to complete one full rotation. With a rotary attachment, the SPR setting determines how precise and accurate the rotary motion is.

The controller must be configured to match the stepper motor that drives the rotary axis. Every CO2 laser from AEON Laser USA ships with rotary settings on its USB drive, for every rotary type we offer. Those settings are generic, though, and may need tuning to make file dimensions come out right.

If your engraving comes out elongated or squished along the Y axis, the SPR setting likely needs adjusting. SPR only affects Y axis dimensions, and only when the machine is in rotary mode.

Identify an SPR issue

Run a test file with the rotary and look at the result. Hold the cup upright, as if to drink from it. If the design looks visibly stretched or compressed around the cup, the SPR needs attention.

Consider how precise your file needs to be. On a simple name or a small design, a minor sizing error is less noticeable. On a full wrap, the SPR must be precise for the edges of the design to meet cleanly.

Adjust the SPR

Before you start, make sure that the rotary settings are loaded, the cup or item is set properly in the rotary, and it is at the correct focal distance.

1. Set up a 10 mm square in LightBurn, in Line mode, at a speed of 50 mm/s and 30 to 40% power, and send the file to the machine. For larger designs or full wraps, use a 100 mm by 10 mm rectangle instead. The process is the same.

   

2. Run the file on the cup.

3. Take the cup off the rotary and measure the engraved length along the Y axis. The Y axis lines are the ones engraved while the laser head stayed still and the rollers turned the cup. They are typically the top and bottom lines when you hold the cup upright.

   

   From this point, it is critical to measure as precisely as possible. Measure from the center of one engraved line to the center of the other, at the corners of the box. For a 100 mm rectangle, use a cloth tape measure, because calipers do not measure the curve accurately.

4. Calculate the new SPR value:

   New SPR = old SPR ÷ measured length × intended length

   For example, with a current SPR of 25000, a measured length of 18.43 mm and an intended length of 10 mm, the new SPR is 13564.84.

   

5. Enter the calculated SPR in the “Pulses per rotation” box, under “Rotary Parameters” in the LightBurn Machine Settings window. Rounding to the nearest whole number is acceptable. If you keep decimals, keep at least three decimal places.

   

6. Click “Write” in the Machine Settings window to update the SPR value.

   

7. Reposition the cup and run the square test again. You do not need to resend the file: the change only affects how the motor moves, not the dimensions set in the file.

8. Measure the new square.

   

9. The square should now be within tolerance (plus or minus 0.5 mm), provided the first measurements were precise. If not, repeat the process.

10. Return to LightBurn. Save the adjusted settings and overwrite the ones on the flash drive for future use.