Two-sided tumbler engrave — alignment checker
Engraving both sides of a tumbler puts the second design half a turn from the first. If the rotary is calibrated to a cup that is not the cup on the chuck, that half turn is not half a turn — and the same error stretches the art around the cup. Both symptoms come from one number. Enter what the rotary is set to and what you measured off the tumbler to see the gap before you burn it.
What this can't tell you. This only explains errors that come from calibration. If your numbers check out here and the monogram is still crooked, the cause is mechanical or in the file — a chuck that slips mid-burn, a tumbler that is tapered rather than straight-walled, or art that was not centered before it was sent.
Up to 3 letters, engraved on both sides.
The numbers you typed into LightBurn or the controller.
≈ 3.54 in
Calipers on the real cup, at the height you are engraving.
≈ 3.39 in
Advanced: steps per rotation
Only touch this if your rotary is mechanically mis-stepped — a changed pulley or belt, or a driver set to the wrong microstepping. A stock rotary turns the steps it is told to, and the diameter above is the whole story.
The wall unrolled flat — dashed is where side 2 belongs, solid is what the machine will actually engrave.
Why a wrong diameter moves side 2, not just the size
The rotary has no idea how big your cup is. To slide the art sideways it converts millimetres into steps using the two numbers you gave it — steps per rotation and circumference. If either does not match the tumbler on the chuck, every sideways distance comes out multiplied by one factor:
k = (steps set ÷ steps actual) × (circumference actual ÷ circumference set)Everything in the wrap direction scales by k together. The monogram stretches or squashes around the cup by k, and side 2 — which the file places half a wrap away — lands at 180° × k. Dial in a circumference that is too small and the machine over-spins: art stretched, side 2 past 180°. Too big and it under-spins: art squashed, side 2 short. A steps error does the same thing, usually smaller.
Height up the cup is the laser's own axis and is never touched. That is the tell: if your monogram is wrong in one direction only, you are looking at calibration.
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Numbers check out and it's still wrong? Submit a ticket — US-based support, fastest response times in the industry.