How do I calculate steps per rotation for a laser rotary?

Multiply the motor’s full steps per turn by the driver’s microstepping and the rotary’s gear ratio. LightBurn’s own example is 200 × 8 × 2 = 3,200 steps. Then press LightBurn’s Test button: the rotary should turn exactly once and return. If it turns too far, lower the value; if not far enough, raise it.

What is mm per rotation in LightBurn for a GRBL laser?

GRBL lasers that drive the rotary from the Y motor port ask for the distance of commanded movement that turns the rotary once. Rotary makers usually supply it — xTool lists 32 mm for the RA2 Pro roller and 128 mm for its chuck. If yours does not, a LightBurn forum formula is steps per rotation ÷ the Y steps/mm ($101), used as a starting point before testing.

Does the cup diameter matter on a roller rotary?

Not for the output. On a roller rotary the object turns at the same surface speed as the rollers, so only the roller diameter matters; LightBurn says the object diameter does not affect output on a roller rotary. On a chuck rotary the object diameter does matter and must be entered for every object.

How do I engrave a tapered tumbler?

Use the largest diameter for the wrap, shim the small end if the top surface drops more than your laser’s depth of focus, and use LightBurn’s Taper Warp tool (top diameter, bottom diameter and length, in mm) so the artwork is not distorted. For a full wrap on a taper, design on the flat arc-shaped template the calculator draws.

Calculator · rotary

Laser rotary & tumbler calculator

The numbers LightBurn asks for when you set up a rotary — steps per rotation or mm per rotation — plus the wrap length of your cup, how much a tapered tumbler drops out of focus, and the flat arc-shaped template that wraps a taper without distortion.

1Your rotary

Rotary

Rotary type

RollerChuck

Motor full steps per turn

200 for a common 1.8° stepper.

Microstepping

Gear ratio (e.g. 2 for 2:1)

Y steps/mm ($101, GRBL only)

Only for a GRBL laser where the rotary plugs into the Y motor port.

Maker’s mm per rotation (optional)

If the maker gives a value, use it; LightBurn says it is usually supplied.

2Your cup or tumbler

Diameter at the top (mm)

Diameter at the bottom (mm)

Height, measured straight along the axis (mm)

Arc blocked by the handle (mm, 0 if none)

Steps per rotation

—

mm per rotation (GRBL)

—

Wrap length

—

Taper

—

The formulas

Steps per rotation = motor full steps × microstepping × gear ratio (LightBurn: 200 × 8 × 2 = 3,200)

mm per rotation (GRBL, rotary in the Y port) ≈ steps per rotation ÷ Y steps/mm ($101)

Wrap length = π × diameter · printable width = π × diameter − the arc blocked by the handle

Taper half-angle = atan((D_top − D_bottom) ÷ 2L)

Arc template: R_outer = S × D_top ÷ (D_top − D_bottom), R_inner = R_outer − S, sweep = 180° × D_top ÷ R_outer (S = slant length)

The first formula is LightBurn’s. The GRBL one comes from a LightBurn forum answer rather than the manual, and owners report that the tuned value can differ from the roller’s circumference, so treat it as a starting point. The wrap, taper and arc formulas are standard geometry; the arc is how a cone unrolls flat, which is why a straight rectangle of artwork looks skewed on a tapered cup.

Roller or chuck

Roller rotary. The rollers turn the object, so 1 mm of roller surface moves 1 mm of object surface. Only the driven roller’s diameter matters; LightBurn notes the object diameter does not affect output. Grip is the risk: LightBurn recommends a chuck for full-wrap tumblers, or a non-slip wrap or weights on rollers.
Chuck rotary. The object turns with the chuck, so LightBurn needs the object’s diameter for every new object; on a taper, use the largest end. A wrong diameter stretches or squashes the design.

In LightBurn, DSP (Ruida) controllers take Steps per rotation, and GRBL (G-code) controllers take mm per rotation. Choose Y axis if you unplug the Y motor and plug the rotary in, or Z or A axis for a dedicated rotary port (xTool lists Z for the D1 and Y for the D1 Pro). Most Ruida controllers fix the rotary to Y.

Published rotary values

Rotary	LightBurn values from the maker	Object diameter
xTool RA2 Pro	Roller: 32 mm per rotation, roller diameter 17 mm. Chuck: 128 mm per rotation (4:1 gear)	Roller 3–198 mm, chuck 0–100 mm
Sculpfun Rotary Roller	Not found on the maker page	6–150 mm

Tapered tumblers

Lying straight on a roller rotary, the bottom of a tapered cup rests level, so its top surface — where the laser engraves — falls by at least the full difference in diameter along its length (a little more in the valley between two rollers). In a chuck the axis is level, so the top falls by about half the difference. If that is more than your laser’s depth of focus, raise the small end. LightBurn’s Taper Warp tool takes the top diameter, bottom diameter and length (in millimetres only) and bends the artwork to match, but it does not correct the focus.

FAQ

How do I calculate steps per rotation for a laser rotary?: Multiply the motor’s full steps per turn by the driver’s microstepping and the rotary’s gear ratio. LightBurn’s own example is 200 × 8 × 2 = 3,200 steps. Then press LightBurn’s Test button: the rotary should turn exactly once and return. If it turns too far, lower the value; if not far enough, raise it.
What is mm per rotation in LightBurn for a GRBL laser?: GRBL lasers that drive the rotary from the Y motor port ask for the distance of commanded movement that turns the rotary once. Rotary makers usually supply it — xTool lists 32 mm for the RA2 Pro roller and 128 mm for its chuck. If yours does not, a LightBurn forum formula is steps per rotation ÷ the Y steps/mm ($101), used as a starting point before testing.
Does the cup diameter matter on a roller rotary?: Not for the output. On a roller rotary the object turns at the same surface speed as the rollers, so only the roller diameter matters; LightBurn says the object diameter does not affect output on a roller rotary. On a chuck rotary the object diameter does matter and must be entered for every object.
How do I engrave a tapered tumbler?: Use the largest diameter for the wrap, shim the small end if the top surface drops more than your laser’s depth of focus, and use LightBurn’s Taper Warp tool (top diameter, bottom diameter and length, in mm) so the artwork is not distorted. For a full wrap on a taper, design on the flat arc-shaped template the calculator draws.

Sources

LightBurn, Rotary mode (DSP), Rotary mode (G-code), Taper Warp and Full-wrap tumblers.
LightBurn forum, Setting up my custom rotary (mm per rotation from $101).
xTool support, RA2 Pro settings in LightBurn; Sculpfun, Rotary Roller.

Last checked 2026-10-27 · Calculated values; no rotary was used to make this page.