Skew Correction Calculator
The Skew Correction Calculator turns three caliper measurements into Klipper’s [skew_correction] values.
Free, runs in your browser, no registration.
What skew is
Section titled “What skew is”Skew is when your axes aren’t perpendicular to each other. Squares print as parallelograms, circles print as slight ellipses, and boxes don’t fit together even though every individual dimension measures correctly.
It’s the calibration people reach for last, usually after concluding that “the printer is just a bit off.” It’s mechanical, it’s measurable, and Klipper can correct it in software.
Fix the mechanics first
Section titled “Fix the mechanics first”Software skew correction compensates for geometry error. It doesn’t fix the cause, and if the cause is something that will keep moving, you’ll be recalibrating forever.
Check first:
- Frame squareness — measure both diagonals of the frame. They should match.
- Belt tension — uneven CoreXY belts directly produce skew. Run the belt tension calculator first.
- Gantry alignment — on CoreXY, a racked gantry produces skew that varies with position, which software correction cannot fix.
- Loose eccentric nuts or wheels on V-slot machines.
Use skew correction for the residual error that remains after the machine is mechanically sound.
The measurement
Section titled “The measurement”Klipper’s method uses a calibration object with known diagonals — print the standard skew calibration model.
For each plane you’re correcting (XY is the common one):
- Measure AC — one diagonal
- Measure BD — the other diagonal
- Measure AD — one side
Use calipers, measure carefully, and take each measurement two or three times. Skew correction amplifies measurement error — a sloppy reading produces a correction that makes things worse.
Enter the three values into the calculator, or use Klipper directly:
SET_SKEW XY=AC,BD,ADVerify by reprinting the calibration object, then save:
SKEW_PROFILE SAVE=my_skew_profileAnd in printer.cfg:
[skew_correction]XY, XZ, YZ
Section titled “XY, XZ, YZ”Most printers only need XY. That’s where frame squareness and belt tension errors show up.
XZ and YZ skew indicate the Z axis isn’t perpendicular to the bed — a gantry or frame problem that is better fixed mechanically than compensated in software. If your XZ skew is significant, check your Z rails and gantry mounting before reaching for correction.
Common mistakes
Section titled “Common mistakes”- Correcting skew instead of fixing the machine. If the gantry is racked, software correction papers over a problem that will keep changing.
- Measuring sloppily. The maths amplifies error. Measure three times.
- Applying skew correction before belt tension. Uneven belts are a leading cause of XY skew, and retensioning invalidates your correction.
- Correcting XZ/YZ in software. Usually a mechanical problem worth solving properly.
- Forgetting to save the profile.
SET_SKEWalone doesn’t persist across restarts.
Where this sits in tuning
Section titled “Where this sits in tuning”Motion chain: belt tension → input shaping → acceleration limits → skew correction ← you are here
Skew is last in the motion chain because everything above it can cause or change skew.
Related tools
Section titled “Related tools”- Belt Tension Calculator — do this first
- X and Y Offsets Calculator
- Shrinkage Calculator — the other half of dimensional accuracy
- All Calculators
A note on diagnosis
Section titled “A note on diagnosis”If parts are dimensionally wrong but squares are still square, that’s shrinkage, not skew — use the shrinkage calculator instead. Skew is specifically about angles, not sizes.