Text-to-CAD prompts that work
Every prompt below produced a file that passed dimensional checking. They are worth reading as patterns rather than copying verbatim: the structure is what makes them work.
The pattern
[what it is] + [overall size with units] + [each feature, with a diameter and a position]
That is the whole trick. Name the object, give it an envelope, then give every feature a size and a location. Anything you leave out is a number the tool has to invent.
Prompts and what they produced
| Prompt | Result | File |
|---|---|---|
| Mounting plate 120 x 80 mm with four 6 mm holes, one inset 10 mm from each corner | 120 × 80 mm | DXF |
| Mounting plate 200 x 100 mm with six 8 mm holes in two rows of three, inset 15 mm | 200 × 100 mm | DXF |
| Plate 150 x 100 mm with one 40 mm centre bore and four 8 mm holes, one inset 12 mm from each corner | 150 × 100 mm | DXF |
| Plate 100 x 100 mm with 12 mm radius rounded corners and one 30 mm hole in the centre | 100 × 100 mm | DXF |
| Electronics mounting plate 80 x 60 mm with four 3.4 mm holes, one inset 5 mm from each corner | 80 × 60 mm | DXF |
| ASME B16.5 class 150 three inch flange face: 190.5 mm outer diameter, one 90 mm centre bore, four 19.1 mm bolt holes on a 152.4 mm bolt circle | 190.5 × 190.5 mm | DXF |
| ASME B16.5 class 150 four inch flange face: 228.6 mm outer diameter, one 115 mm centre bore, eight 19.1 mm bolt holes on a 190.5 mm bolt circle | 228.6 × 228.6 mm | DXF |
| EN 1092-1 DN50 PN16 flange: 165 mm outer diameter, one 61 mm centre bore, four 18 mm bolt holes on a 125 mm bolt circle | 165 × 165 mm | DXF |
| Gasket 120 mm outer diameter, one 80 mm inner diameter opening, six 8 mm bolt holes on a 100 mm bolt circle | 120 × 120 mm | DXF |
| Gasket 90 mm outer diameter, one 60 mm inner diameter opening, eight 7 mm bolt holes on a 75 mm bolt circle | 90 × 90 mm | DXF |
| Square gasket 100 x 100 mm with one 60 mm circular opening and four 6 mm holes, one inset 8 mm from each corner | 100 × 100 mm | DXF |
| Enclosure face panel 120 x 80 mm with one 22 mm switch hole and four 4 mm holes, one inset 6 mm from each corner | 120 × 80 mm | DXF |
The full set is on the examples page.
Four phrasings that break it
Breaks A washer with a 20 mm radius
Works A washer with a 40 mm outer diameter
Radius and diameter confusion is a documented failure mode in published text-to-CAD benchmarks, and the most common scalar error we see in our own. State diameters. If you must use radius, say the word and check the result.
Breaks A bracket to hold a motor
Works An L-bracket, 60 mm base, 40 mm upright, 4 mm thick, four 5 mm holes
There is no such thing as a default motor, so the tool has to invent a frame size. An underspecified request forces the tool to invent numbers, and invented numbers look exactly like real ones in a CAD file.
Breaks A plate about 100 mm across with some holes
Works A 100 × 100 mm plate with four 6 mm holes inset 12 mm from each corner
Every vague word leaves the tool a number to invent. Corner inset is the dimension most often left out, and it is the one that decides whether the part bolts up. The tool cannot infer it, so it will pick something.
Breaks A 4 × 2 plate
Works A 4 inch by 2 inch plate, or 101.6 × 50.8 mm
Bare numbers get read in whatever unit the tool defaults to. Name the unit, or switch the unit toggle before generating.
When it should refuse
Ask for a 40 mm bore in a 30 mm wide bracket and a good tool tells you that is impossible. Ask for something sculptural and it should tell you parametric CAD is the wrong tool rather than producing a lumpy approximation. If a tool silently returns geometry for either, that tells you what it does with your real requests too.
Try one
Paste any prompt above into the AI CAD generator and compare what comes back against the file linked beside it.
Open the tool