Common issues in CAD design reviews

These mistakes recur in printed parts and assemblies. The list comes from real projects, and each entry links the lesson that recorded it. Every review walks this list, whoever wrote the design and however small the change:

Run cad-agent all. Every row in the report must pass. A row that fails, is stale or did not run is a finding, never a footnote.
Then go through the Review rows below. No automatic check covers them yet, so look at the model, the renders and the sources yourself. Say in the review which ones you checked and how.

When a review finds a new kind of mistake, add it here, in the same PR or in an issue, with the check that would catch it. Once a check exists, move the entry from "review" to the check.

Geometry and modelling

Issue	How it shows up	Caught by	Lesson
A feature added after the holes refills them: a rib, boss, skirt or gusset unioned after the screw holes, counterbores, countersinks or insert bores were cut	The part is a valid watertight solid and every fit, strength and slice check passes, but a screw head will not seat and an insert will not go in. Found on a printed lid: stiffening ribs ran into the four socket-head counterbores	`cad-agent holes` (the "Holes clear" rows, run by `all`): every cylindrical hole and countersink cone in each part's STEP is probed for material inside. Fix the build order so every hole is cut last, after all the added features. Known misses, so look at these in a section view: a hole capped at one end reads as blind, and a counterbore blocked right across with a hole cut through the block reads as a ledge (listed in the result)	03
A rib or boss ends on air: it was placed over a vent slot or an opening cut later	It looks attached in a render, but FEA puts the peak stress at the joint. A rib that is fully detached prints as a loose piece	FEA, plus a section view at each rib end. The "Printed parts" rows (one solid) catch a rib that is fully detached	03
Coplanar or flush unions	Faces that only touch leave seams: two solids, a non-manifold edge, or an open STL	The "Printed parts" rows (single solid, watertight). Overlap joined features by 1–2 mm	—
Parts collide, or a clearance was checked against a bounding box	It fits in the CAD assembly only because something was approximated or left out	Gates relation table; the project's clearance step. Investigate every hit; classify false positives explicitly	07
Walls or ribs too thin to print or carry load	Weak parts; gaps in the slicer preview	The wall gate (`gates`); FEA for loaded parts	10
Overhangs and unsupported bridges in the print orientation	Sagging or failed prints	`cadagent.geometry.downward_area` overhang screen; check in the slicer preview	03
Engraved or embossed text not fused before cutting	Floating islands; an open mesh	"Printed parts" rows (single solid, watertight)	06
Slender columns or insert bosses not tied into a wall	They crack or wobble when the screw is driven	Review: every boss and column has a load path; FEA	03
One weak feature fixed, its siblings left as they were	The same failure on the other three corners	Review: survey all similar features when one is found	03

Bought parts, sources and assumptions

Issue	How it shows up	Caught by	Lesson
The wrong bought part: a similar model, a guessed size, another revision	A printed lid 15 mm too short for the cooler that was actually fitted	Review: identify the exact part (vendor, part number, datasheet, photos) before sizing anything around it; record it	10
A photo read in the wrong orientation, or a flow direction assumed	Features on the wrong side; a CFD with the fan blowing the wrong way	Review: record the user's observations (measurements, "the fan blows up") with the date, and check assumptions against them	01
Connector windows sized from a bounding box or the board connector, not the mating plug	The cable's overmould does not fit	`cadagent.connectors`: windows from the modelled mating plug, plus a sweep check	03, 05
A vendor model used as if it were measured data	Hidden errors in mounting holes or heights	Review: say which bodies are proxies	01
Vendor files committed or redistributed	A licence problem; a leak that cannot be undone	Review the package and release include lists; fetch references with a script	agent workflow

Fasteners and assembly

Issue	How it shows up	Caught by	Lesson
Screw length from the wrong datum, or too little thread engagement	Strips, or bottoms out	The fastener gate; compute the stack plus the engagement; print a coupon	04
No tool access at the step where a fastener goes in	It cannot be assembled in the documented order	The assembly-access gate; the assembly-step renders	04
Inserts, countersinks or D-holes sized without a test print	Loose inserts; bulkheads that turn	Coupons printed before the big parts	04
Cable routes at an impossible bend radius, or tie anchors in the path	Cables that cannot be routed	Review: route from the real mating direction with a stated bend radius	05

Evidence, simulation and release

Issue	How it shows up	Caught by	Lesson
Stale evidence: reports, renders or results from before the last change	A pass for geometry that no longer exists	Hash-bound results (slice report, hole check, gates, CI parameter check); rerun `cad-agent all` after every geometry change	07
Exports that change bytes on every rebuild	The slice report goes stale with no geometry change	Reproducible 3MF writer; check `git diff` after a rebuild with no change	07
A simulation trusted before it converged, balanced and was calibrated	Confident but wrong temperatures or stresses	The project's simulation checks: steady, energy balance, calibrated, and inputs that match the design (fan axis and position)	10
Material savings judged on CAD volume	The slicer disagrees by tens of percent	`cad-agent slice`	10
A render or report published without being looked at	Wrong colours, clipped views, a stale picture	Review: open every image before it is shown	07
Claims stronger than the evidence	"No re-breathing", "fits", "strong enough" from a model only	Review: every claim names its evidence and its limits; nothing physical is claimed without a print	07