Remix a downloaded STL

You downloaded an L bracket from a model site. It's nearly right, but you want slots instead of its two screw holes, so you can adjust it, and gussets to stiffen the corner. You ask for that in plain words; the assistant changes the model and gives you files to print.

What is real here

The pictures and numbers come from a real run of the server, using the bundled remix_bracket example (CC0) as the "download". What you and the assistant say is paraphrased. Under each step, What the assistant did shows the tool calls, for the curious.

Set up first: the Quick start, and ideally your printer (first tutorial, step 2).

1. Check the license

On the model's page, find the license. -ND (no derivatives) means no remixes: stop there. -NC means not for sale; BY means you credit the author when you share. Tell the assistant the license and the page's address; it records them with the part.

2. Give it the file

"I want to remix ~/Downloads/l_bracket.stl: slots instead of the two holes, and add gussets. It's CC0, from ."

The assistant gets the file to where the server can read it, in the part's ref/ folder. How depends on your app:

• Apps that can work with files on your computer (Claude Code, Antigravity, Cursor and similar): the assistant copies or uploads the file itself. On a shared server it uploads it with a short-lived upload link. You do nothing.
• Small files can also go straight through to the server as part of the request.
• Apps that can't open files on your computer (a chat-only app): attaching the STL to the chat lets the assistant see it, but not the server. The assistant tells you which folder to drop it in (on your own machine), or gives you a one-line command that uploads it (on a shared server).

What the assistant did

upload_reference(part="l_bracket_slots", filename="l_bracket.stl"). On your own machine the answer is the folder to copy it to. On a shared server it is a signed upload link (curl -fT <file> '<link>', no token needed, expires), or over SSH a b123d-print push command. With data_base64 the assistant sends the file's content directly (practical for small files). Details: Remixing a part.

3. It looks at the original

It's 50 × 30 × 30 mm, which looks right for a bracket, so the units are millimeters. It has two 4.5 mm screw holes in the base and a 6 mm hole in the upright. It's mostly flat faces, so I'll change it directly rather than redraw it.

If the size had looked wrong (a "bracket" 2 mm long), the file would have been drawn in inches, and the assistant would say so and load it with inch units.

What the assistant did

describe_model, which reports the size, the units, the holes it finds and whether to modify or redraw the model.

4. You agree on the plan

The assistant lists each change and its size, and waits:

Change	Size
slots over the two screw holes	4.5 mm wide (same screws), 10 mm of adjustment
two triangular gussets	3 mm thick, 14 mm up the corner, clear of the slots

The 6 mm hole in the upright stays. OK?

You say "yes".

5. It makes the change and checks it

Done: slots and gussets added. It passes the printing checks. One note: the top of the 6 mm hole in the upright overhangs a little. That was in the original too, so I left it alone. Say if you want it fixed.

The assistant also measures how much the remix differs from the original. Red is what changed (the old holes, now slots), grey is new (the gussets), green is untouched:

What the assistant did

new_part and write_part: the script loads the original with import_model and cuts and adds to it, with the license in its header (the remix_bracket example is that script). Then build_part, check (the overhang is marked "inherited from the original"), before_after and compare. A remix should fail compare's "is this the same part?" test; the picture is the useful part (inherited findings, comparing parts).

6. A test plate, then the files

"Make a test plate for the base."

It cuts a thin plate from the bottom with the slots in it. It prints in minutes; hold it against whatever the bracket screws to before printing the real thing.

Then it exports the remix to parts/l_bracket_slots/out/ in your project folder: the 3MF and STL for your slicer, and pictures. On a shared server the assistant brings the files home before it's done, the same as in the first tutorial.

Slice the 3MF as usual (From part to print).

What the assistant did

make_template(kind="face", face="bottom") and export(formats="stl,3mf,png"); on a shared server, download_part too.

7. Share it with credit

The assistant ends with the line to use when you post the remix:

Remix of "L bracket" by b123d-print contributors, CC0 1.0,

For a BY license that credit is required; for -NC, the remix isn't for sale either.

Next

• Remixing a part: units, modify vs redraw, and the rest.
• Your first part, if you skipped it.