Rotary attachment calculator

Steps per rotation and mm per rotation for roller and chuck laser rotaries, object circumference and the usable wrap-around width, for LightBurn, xTool and GRBL machines.

Engraving tumblers, bottles and rings means telling the software how far the object turns per motor step. Enter the object and roller diameters and the axis settings, and get the steps per rotation for a roller rotary, the steps per rotation for a chuck rotary and the circumference you can wrap a design around.

Roller or chuck

On a roller rotary the object rests on two rollers and turns because they turn: one roller revolution moves the surface of the object by the roller circumference, so the setting is about the roller, not the object. On a chuck rotary the object is clamped to a shaft: one shaft revolution is one object revolution, so the setting is the steps the motor takes for one turn of the shaft, and the software works out the surface distance from the object diameter you give it.

Checking the numbers

• Engrave a 20 mm square on a round test piece. Measure its height around the curve; if it comes out 22 mm the steps per rotation are 10 % high.
• On a roller rotary make sure the object does not slip: a rubber band around the roller fixes most of it.
• Tapered cups: tilt the rotary (or shim it) so the engraved face is level, and expect the far end to turn a little slower.
• Keep the focus on the top of the curve; the depth of focus calculator tells you how much the surface may fall away at the sides.

Related tools

• Inlay kerf offset: How far to grow the insert and shrink the pocket so an inlay fits without a gap.
• Sheet gauge ⇄ mm: Gauge to millimetres and back for steel, stainless, aluminum and SWG, with the tables.
• Nesting efficiency calculator: Compute utilisation, waste and material cost from total part vs sheet area.

FAQ

LightBurn asks for mm per rotation, which number is that?

On a roller rotary: the roller circumference, π × roller diameter (the second result). On a chuck rotary LightBurn asks for steps per rotation instead, the fifth result, and takes the object diameter separately.

Where do I find the Y axis steps per mm?

In the machine settings of your controller: $101 on GRBL, the Y axis step setting in Ruida, or your machine's configuration page. 80 is common for GRBL diode machines with 16× microstepping and GT2 belts.

My engraving is stretched around the object.

Steps per rotation is too low (object turns too far per step) or, on a roller rotary, the object slipped. Run the 20 mm square test and scale the setting by measured ÷ drawn.