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Edit an STL or 3MF
Modify a model you downloaded, without learning CAD
The Thingiverse download is 4 mm too narrow, the lid needs a cable slot, the bracket wants two more screw holes. Meshes are hard to edit because they are triangles, not dimensions. Upload the STL or 3MF to SpeakCAD and say what to change: the AI adds to it, cuts into it or rebuilds it as a parametric model with the same size, and you download a fresh STL, 3MF or G-code sliced for your printer.
How it works
Upload, describe the change, check the ghost, download
A mesh edit is one message: the file and a sentence with the measurements. The previous version stays visible as a ghost, so you see exactly what moved.2
Say the change with numbers
“Add a lid with a 0.3 mm clearance”, “cut a 12 mm hole through the centre of the top face”, “make the base 3 mm thicker and add four rubber-foot recesses”. Features are placed from the outer size of the mesh. The file and the sentence are one AI request (2 credits).3
Or ask for a parametric rebuild
“Rebuild this as a parametric model” turns the mesh into a clean model with the same overall size, where every dimension is a named number. Give the hole positions or a photo with a ruler for the detail the AI cannot see.4
Check against the ghost
The edited part renders on the virtual bed with the previous version as a ghost. The first render usually appears within a minute or two: a new part goes to the strongest models, which reason through the geometry, and small edits land in seconds. Tap a face to read a size, type a number in the dimensions panel, undo: all free.5
Download STL, 3MF or G-code
Download the result as a watertight STL or 3MF, or as G-code sliced with the official profile of one of 380+ printers. Small fixes after a download re-download free.What an edit costs
| Step | Cost |
|---|---|
| Live demo: 3 AI edits of a real part, no account | Free |
| Uploading the file with the change to make (one AI request) | 2 credits |
| Each change by chat | 2 credits |
| Typing a new number in the dimensions panel, undo | Free |
| STL or 3MF download | 10 credits; small fixes after it re-download free |
| G-code sliced for your printer | +5 credits per slice without Pro or Unlimited |
| Starter credits | $5 once = 75 credits, about 4 parts with a couple of edits each; no subscription |
| Pro | $9.99 a month: 200 credits a month, sliced G-code included |
| Unlimited | $24.99 a month: unlimited requests and downloads |
Edits that work in one message
Attach the mesh, paste one of these, change the numbers to yours.“Add a snap-fit lid to this box: 2 mm thick, 0.3 mm clearance all round, two cantilever clips on the long sides, and a 8 x 4 mm notch on one short side for a cable.”
Open this prompt in the editor“Cut a 6.5 mm hole through the centre of the top face for an M6 bolt, with a 11 mm hex recess 5 mm deep on the underside for the nut. Keep everything else as it is.”
Open this prompt in the editor“Rebuild this bracket as a parametric model with the same outer size (see the bounding box), then make it 20 mm wider and add a third screw hole on the same 40 mm pitch.”
Open this prompt in the editorWhat SpeakCAD does with a mesh, exactly
An STL carries no dimensions, only triangles, so no tool can "change the hole diameter" of a mesh the way CAD changes a sketch. SpeakCAD works around the mesh instead of inside it:
- Add. A lid, a base, feet, mounting tabs, text, a hook, a second part that mates with it. New geometry is placed from the outer size the browser measured (a lid on the top face, a plate under the bottom face) and merged with the original.
- Cut. Holes, slots, windows, a chamfer on the bottom edge, a pocket for a magnet. Cuts go through the original triangles at the position you give.
- Rebuild. The mesh becomes a clean parametric model of the same overall size, with named dimensions you can edit forever after. This is the right move when the download is "almost right": you get the shape back as numbers, then change the numbers.
- Stretch. One axis can be scaled, but the holes stretch with it. When holes matter, rebuild instead: why scaling to 110 percent breaks every hole.
What it does not do: move or resize a feature that sits inside the mesh without being told where it is. The AI receives the mesh's outer size, not its holes and pockets, so "make the existing hole bigger" needs the hole's position and size in the message, a tap on that spot in the 3D view, or a photo with a ruler. Give them up front: a feature placed from a guess can look right on screen and still miss on the print.
Typical jobs
- A Printables organizer that has to be 12 mm narrower to fit the drawer.
- A phone stand from Thingiverse that needs a slot for a thicker cable.
- Your own print from last year, now needed in three sizes.
- A replacement lid for a box whose lid was lost, from the STL of the box.
- A logo or a name on the front of a case you downloaded.
- Four more screw holes in a bracket, on the same pitch as the two it has.
Files it accepts
STL and 3MF as the mesh to modify, images as references, and .scad to continue a parametric design that already exists. STL and 3MF must be watertight for the boolean operations to produce a watertight result; a broken download is best rebuilt parametrically rather than repaired.
On a phone
Open the STL from Files or Downloads directly into the chat, describe the change, and the render appears in the same tab. Downloads go back to Files, ready for the printer's app or SD card. Nothing to install.
Questions
Not by scaling: scaling to 110 percent scales the holes, the clips and the wall thickness with it. Ask SpeakCAD to rebuild the model as a parametric part with the same overall size (say where the holes and clips are and how big, since the AI only measures the outer size), then change the one dimension that is wrong; holes and clearances keep their sizes.
Yes: ask for a parametric rebuild and the AI writes a clean OpenSCAD model matching the mesh's outer dimensions, with every size as a named parameter. Detail inside the mesh (hole positions, wall thickness) is taken from your message or from a photo with a ruler, since the mesh itself only provides its bounding box.
STL and 3MF as the mesh to modify, images as references, and .scad files to continue a parametric design. Downloads are STL, 3MF, the OpenSCAD source, or G-code sliced for your printer.
Yes. Added and cut features are merged with the original triangles, and the download is the union: one watertight STL or 3MF when the upload was watertight. A rebuild replaces the mesh with the new parametric model.
Yes. Download it, or save the text block that starts with “solid” as part.stl, attach it in the chat and say what to change. For a part ChatGPT designed, pasting its description is often better: SpeakCAD rebuilds the part from the numbers as a clean parametric model instead of patching ChatGPT's triangles.
Yes, any STL or 3MF. Check the licence of the model if you plan to share the modified version; editing for your own print is fine.
Starter credits: 75 credits for $5 once (50 + 25 free), no subscription. Pro $9.99/mo (200 credits a month, sliced G-code included); Unlimited $24.99/mo (unlimited requests and downloads). Turning the model around in 3D and changing its numbers in the viewer are free; each AI request (a new part or a chat edit) spends 2 credits, whichever model answers; a download spends 10 credits (+5 for G-code sliced for your printer without Pro or Unlimited); small fixes after a download re-download free. Undo and turning the model around in 3D are free too.
Start from something that exists
How to modify a Thingiverse or Printables model so it fitsResize, add a hole, change the lid: the three edits people make most.Add text, a hole or a mount to a model you downloadedWithout learning Blender.Duplicate a physical objectNo file at all? Two phone photos next to a ruler give a parametric copy.From a ChatGPT description to a fileWhen the assistant wrote the part but could not export it.Text to STLNo file to start from: describe the part in millimetres instead.Check a model before you downloadDimensions panel, overhangs, the ghost of the previous version.