MeshWright

AI CAD gets scored on shape, which was always the half that worked. Chamfer distance, overlap, a render that matches. Each compares a frozen result to a target and stops there. The test that counts comes later: change one dimension and see what is still standing.

The only error that survives every check is a unit error. An STL stores numbers, not millimetres. Watertight, clean fits, small residuals: all scale invariant. Nothing in the file objects to a part 25.4 times too big. Only a measured dimension catches it.

A feature tree rarely breaks on a dimension, it breaks on a reference. The number updates fine. What fails is the sketch dropped on a face, and the fillet holding an edge the rebuild renamed. Reference what you made on purpose: planes, datums, construction geometry.

A round part on a turntable comes back rounder than it is. Spin a featureless cylinder and registration has nothing to lock onto. Frames slide until they agree, and ovality is what disagreement looks like. The lobes average out and the alignment reads clean.

Half the dimensions on a part you copy are not measurements, they are lookups. Bearing seats, thread pitch, o-ring grooves, keyways. Someone published those numbers decades ago. Measure them and you get this part's wear. Look them up and you get what it was made to.

Fit a plate's two faces separately and thickness depends on where you ask. Two free planes never come out parallel, so the gap drifts across the part. Fit them as a pair, one shared normal. Thickness is one number, and the residuals say if the taper is real.

Scan to CAD is a measurement problem in modelling clothes. The solid is the half that got easier. Which bump is a feature, which face seats, which diameter was once a drawing number: none of that is geometry. Model a misreading perfectly and it is still a misreading.

A meshed bore is never round, and never the right size. Tessellation lands vertices on the cylinder and the flats inside it. Each facet cuts a corner off the arc. Flat to flat reads undersize, corner to corner reads nominal. The caliper is reading your export setting.

A dimension you typed is not a parameter, it is a number that happens to be editable. A parameter earns the name when something depends on it. Change the bore, and the clearance and the boss move with it. Most trees called parametric are a drawing with extra clicks.

One stray point outvotes a hundred good ones in a least squares fit. Squaring the error is the trick and the problem. A point ten times further out pulls a hundred times harder. Dust on a seating face tilts the plane. The clean surface gets the blame. Trim, then fit.

Prompt to CAD asks you to describe a part you already hold. The mesh has every radius, every worn step, every bore that came out oval. Your sentence has what you thought to mention. Text is how you author something new. It is a strange way to copy something old.

An STL does not know which of its triangles touch. Every facet carries its own three corners. No vertex table, no edges, no neighbours. Your importer rebuilds adjacency by matching points inside a weld tolerance you never set. Too loose and a thin wall welds shut.

Nobody recovers design intent from a scan, the modeller assigns it. A mesh holds a surface. It never says which face was the datum, which radius was cosmetic, or which diameter mattered. You pick all three, and the tree is where your pick becomes someone else's fact.

Matting spray shrinks every hole and grows every shaft. It is a coating with thickness. On a shaft it adds, in a bore it eats the diameter, so shaft and housing drift toward each other. Spray both halves of a fit and the clearance you measure is one you created.

Plenty of parts arrive for scanning that a pair of calipers would have finished by lunch. Flat, prismatic, four holes on a pitch. You scan a part you already understand, then pay again to fit planes back out. A scanner earns its keep on shapes you cannot write down.

Below about 120 degrees of arc, a circle fit is no longer measuring the radius. Centre and radius trade off along one direction. Noise a full bore would shrug off slides the centre out and inflates R to match. Residuals stay small. Fillets are where this bites.

A generated model nobody graded against the scan is a guess that renders well. Shaded geometry forgives everything. A seal face can sit off where it mates and still look right. Fit a primitive and the residuals say so out loud. Generation demos. Grading defends.

A mesh does not know where its edges are, you set that with a threshold. Nothing in the file marks a crease. Two facets read as an edge when the angle they meet at clears a setting, often 30 degrees. Raise it, a chamfer joins the wall. Lower it, a flat face grows ribs.

Fully constrained means the numbers agree with each other, not with the part. Fully defined and fully invented look identical to the solver. In a traced sketch some numbers are measured, some rounded, some guessed. Record which. In a year they all read as fact.

A part straight off the machine scans oversize, and the mesh is not wrong. Warm aluminium moves further than steel. Cutting fluid, a hot spindle, a bench in the sun: all of it arrives as geometry, never as a note. Your scan is true at a temperature nobody wrote down.