Find your printer's real numbers

Two test prints that replace every guess about overhangs, wall thickness and fit — and where each number goes afterwards.

Almost every print-aware decision in OwlCAD rests on a number about *your* machine. Does this face need support? Is that wall too thin to lay down? How much slack does this joint need? Every default answer is a reasonable average and none of them is your printer, your filament and your slicer. Two prints replace the lot, and you only do it once per material.

The block is derived from your nozzle, not from ours. This is why it is a generator rather than a download. A wall comb built for a 0.4 mm nozzle starts three stations above anything a 0.2 mm owner can use, so a fixed test block is a test of somebody else's machine. Set the nozzle first and every ladder — walls, clearances, gaps, bridges — re-derives around what yours can actually resolve.

Slice it wrong and it lies to you, politely. Supports prop up the overhang fins, span the bridges and fill the fuse gaps; all three banks then print beautifully and tell you nothing. A raft lifts the first-layer block off the bed, which is the only place elephant foot happens. These are not fussy preferences — they separate a measurement from a decoration.

The fit coupon answers the one question the block cannot. How much slack a joint needs is not a property of the design, it is a property of your process, and the usual way to find it is to print a joint, discover it binds, and print it again. The coupon collapses those three prints into one: a row of holes stepping through a clearance range, each engraved with its value, and a gauge pin at nominal beside it. Push the gauge in from the tight end; the first hole it enters is your number.

Then actually use it. This is the step people skip. Every joint generator — snap-fit, pin hinge, ball joint, the bearings and the plugs — carries a Fit control with Tight, Normal, Loose and Custom. Set Custom to the figure you measured and the joint is cut for your machine instead of for an average one. The same number belongs in the clearance modifier when you are fitting parts by hand.

Two of the readings are not ours to take. Stringing and first-layer squish belong to your slicer profile; OwlCAD reads neither and writes neither. The block measures them because you are printing a test anyway and it costs nothing to put them on the same plate — but the place they go is the slicer, and the block says which is which so nothing gets typed into the wrong tool.

Do it again when something real changes. A new filament brand, a new nozzle, a different material family — those move the numbers. A new colour of the same PLA does not. It is a twenty-minute job you do a handful of times a year, and it stands between a printed joint working first time and a drawer of near misses.

1. Open the Generate panel and pick Calibration block (under Calibration). Set Nozzle diameter first — every ladder on the block is derived from it, so a 0.2 mm nozzle gets a different block from a 0.4 mm one.
2. Switch off any bank you do not need. The plate repacks itself around what is left and the Footprint row says whether it still fits your bed.
3. Slice it with supports off and no raft, in the material you actually build with. Supports would prop up the overhang fins and fill the fuse gaps, so three banks would read as passes. A brim on the plate is fine; keep it off the loose first-layer block.
4. Print it, then read each bank off the part — every value is engraved beside the feature it measures.
5. Now pick Fit test coupon from the same group, choose Pin & hole or Tab & slot, set the nominal size you actually build with, and print the plate and its gauge.
6. Work the gauge along the row from the tight end. The first station it enters cleanly is your printer's real clearance.
7. Put the numbers where they belong: overhang angle and minimum wall go in the 3D Print panel; the clearance goes into any joint's Fit control on Custom. The stringing and first-layer readings go in your slicer, which OwlCAD does not write.