The 45° overhang rule is wrong (and what the measurements say instead)

Almost every design guide for metal 3D printing says the same thing: keep overhangs above 45° or add supports. It is a useful first approximation and it is not what the published LPBF data shows. The measured self-support boundary is 15–20°, not 45° — and the band between them is not free either, because faces that build fine can still come out rough or curl.

Two different things get collapsed into “overhang problem,” and separating them is most of the value:

• Build survival. Below roughly 20° from the plate, an unsupported downfacing face genuinely fails — it droops, dross forms, and the edge can rise into the recoater’s path.
• Surface quality. Between about 20° and 30° the face builds, but it comes out rough. That is a finish penalty and a machining-stock question, not a build-survival flag, and calling it a failure trains people to ignore the flag that matters.

What the studies actually printed

These are the sources behind the two thresholds this screen uses, listed so you can check them rather than take the number:

Six studies, five alloys, and the failures cluster at 15–20° while the successes run down to 24–25°. A 45° cutoff rejects all of it. That is not a safety margin — it is supports and post-processing you paid for on geometry that would have built.

The exception runs the other way: if your machine’s own qualified angle is stricter than these, it governs. If it is more permissive (a Velo3D SupportFree entry, for example), that supersedes both. The machine’s nominal angle is an input, not a suggestion.

Super-elevation: why the edge curls up

The downfacing edge of an overhang is melted over loose powder. Powder conducts heat far worse than solid metal, so that edge stays molten longer, cools through a bigger gradient, and contracts harder than the material behind it. The edge rolls upward. It is one of the four failure modes fully predictable from geometry, because the entire driver — the overhang-angle distribution and the downfacing area — is a shape property.

Super-elevation matters twice. It is a dimensional error on its own, and it is the first step toward a recoater strike: an edge that has curled is an edge standing above the powder bed. The recoater-strike page covers where that goes.

The staircase number you can actually check

Roughness on an inclined face has two parts, and only one of them is geometry. The staircase component is exact: for a surface inclined α from horizontal built in layers of thickness t, the cusps have height t·cos α, and the arithmetic mean deviation is Ra = t·cos α / 4. The screen computes that per face, area-weighted, in micrometres — a number you can put a profilometer on.

Check a part

Every gate named on this page runs automatically on an uploaded STL or STEP at amprintanalyzer.com — free, no sign-up, and the geometry is never modified. Findings are pinned to the model and each one is labeled by its evidence class: measured (a direct geometric fact), screening (a dimensionless index that localizes risk), or estimate (a planning number with its assumptions stated).

If the screen disagrees with something you have actually measured on a printed part, that is the useful case — say so through the feedback strip. Disagreements are the calibration data.