Step 1: Print and Measure a Cube
Print a standard 20 mm calibration cube with your normal profile — same filament, same speed, same nozzle temperature you use for production. The point is to capture how your machine actually behaves, not how it could behave.
Once it is cool, measure the X and Y dimensions with digital callipers. Read at the midpoint of each face, not at the corners — corners catch elephant foot or bulge that does not represent the bulk of the print.
- Measure to two decimal places (most digital callipers do this natively).
- Take three readings per face and average them — cubes are not perfectly square.
- Skip the Z dimension. Z is set by your layer count and is rarely the source of fitment problems.
Step 2: Enter Nominal vs Measured
In the calculator, set Nominal Cube Size = 20 mm and enter your Measured X and Measured Y in millimetres. Also enter your slicer's current Flow Rate as a percentage (typically 100 if you have not changed it).
The tool returns three numbers in real time:
Corrected Flow Rate
Punch this into your slicer's flow / extrusion multiplier. Typical values: 95–102%.
XY Shrink / Expand
Goes into "Horizontal Expansion". Negative means the slicer should shrink each layer slightly to compensate for over-extrusion.
Peg / Hole Clearances
The exact offsets MegaSlicer Pro should apply when generating alignment keys. Feed these back into Slicer Pro and DowelPro.
Step 3: Pick Your Material
The Material dropdown (PLA / PETG / ABS / Nylon / Resin) tunes the recommended clearances, because each plastic shrinks differently after cooling:
- PLA — minimal shrink (~0.1%). Default clearance 0.2 mm.
- PETG — slight stringing tolerance, slightly stretchier. 0.25 mm.
- ABS — pronounced shrink (0.7–0.8%). 0.35 mm.
- Nylon — stretches post-cooling, also absorbs moisture. 0.4 mm.
- Resin — barely moves after cure. 0.1 mm.
Step 4: Verify with the Hole Test
Optional but worth twenty minutes: print a small test piece with a 5 mm peg and a 5 mm hole, measure both with callipers, and enter them in the Hole Nominal / Measured fields.
The calculator cross-checks the XY shrink number against the actual peg/hole behaviour and refines the clearance suggestion. This catches the case where the cube reads true but holes still come out tight — a sign of slight over-extrusion that horizontal expansion alone misses.
Pro Tip — One Cube Per Filament
Re-run this calibration every time you swap brands or even spool batches. The same machine can print 100% flow on a budget PLA and 96% on premium silk PLA — that 4% gap is the difference between a peg that snaps in and one that needs sandpaper.
Apply the Numbers
- Drop the corrected flow into your slicer's filament profile (PrusaSlicer: Filament → Extrusion multiplier; Cura: Flow; OrcaSlicer: Filament → Flow ratio).
- Set the horizontal expansion per-object (PrusaSlicer / OrcaSlicer) or globally (Cura "Horizontal Expansion").
- Feed the clearance values into Slicer Pro's peg-clearance setting and DowelPro's dowel-fit slider.
After this pass your alignment keys should snap together with a satisfying click instead of needing a hammer or a file.
Pairs Well With…
- Slicer Pro — the calibrator output is the source of truth for the clearance sliders that drive its alignment keys.
- DowelPro — the same numbers feed the dowel-fit slider for press-fit dowels in finished assemblies.
- Print Failure Diagnoser — if your symptom is "everything looks puffy" or "tiny features missing", run this calibrator first before changing slicer settings at random.