OneCAD/skills/solidcraft-modeling/SKILL.md

name, description

name	description
solidcraft-modeling	Use when building a new part, enclosure, bracket, plate, flange or any other 3D solid in SolidCraft through its MCP server (tools such as batch, execute, measure, screenshot), or when a SolidCraft session is using many tool calls or tokens.

SolidCraft modeling

Overview

Work the part out as numbers first. Then build it in a few large batch calls, and check each stage with measure against values you computed yourself. A clean build takes 3-4 build batches, about 10-13 calls with the checks. Command shapes, plane axes, ids, reply sizes and known traps are in reference.md next to this file, so you do not need to explore the command catalog.

Before the first call

1. Read reference.md.
2. Run inspect_design {"measure":false,"sketches":false}, even when you think the session is empty.
   • The SolidCraft server's instructions end with Backend: connected to the SolidCraft app when it drives the user's open app, and with Backend: headless otherwise.
   • If the design has timeline features, ask before calling new_design or open, because both discard unsaved work. You can also build into the open design.
3. Write a plan:
   • the parameters
   • the placement: centre the part on the origin so patterns and mirrors can work from the planes
   • every feature, with the world point you will use for each edge or face pick
   • the expected volume and bounding box

Build

• Stages: use one batch per stage:

  1. parameters, sketch, dimensions, finish and the first feature
  2. fillets and shell
  3. holes, cuts and patterns

• Failures: a batch is all-or-nothing. On failure, read failed.index and failed.error, fix that step only, and send the batch again.

• Risky steps: put a risky step in a batch of its own, so a failure does not roll back the work around it. This covers booleans between curved faces that touch, and anything you have not done before.

• Reply size: in large designs, pass "verbose": false to batch and execute.

• Sketch ids are predictable, so later steps in the same batch can use them:

  • Each sketch counts each kind from 1 (l1, c1, a1, p1).
  • Count what the earlier steps of that sketch created. For example, rectangle.center makes l1-l6 and p1-p5.
  • Do not split a batch just to read ids back.

• Positions that must follow a parameter come from:

  • sketch dimensions to "origin" with expression values ("w/2 - wall - 6")
  • expression fields such as solid.cylinder base:["w/2-6","d/2-6","wall"]

  A plain number never follows a parameter.

• Repeats: solid.pattern.rectangular takes expression spacing; solid.mirror takes XY/XZ/YZ, a construction plane or {origin, normal} (origin coordinates may be length expressions such as ["half", 0, 0]). A mirror or pattern feature cannot be mirrored or patterned again.

• Edge and face picks snap to the nearest edge or face. There is no distance limit and no error, so compute the exact midpoint from your geometry (the vertical corner edge of a centred box is [w/2, d/2, h/2]).

  • Picks must be plain numbers.
  • A pick is resolved once and then follows its edge when parameters change.
  • A face can be given by name instead of a point (faces:["F1:+z"], the face of sheet.convert). body_topology lists each face's name, a point that lies on it (the centroid of a face with a hole is in the hole) and, for a cylinder, {origin, axis, radius}.

• Profiles: extrude takes every region by default. For a ring or a boss with a hole, pass profiles.

• Order: fillet the outside edges before you shell, so the shell follows the fillets. An edge of the face the shell removes, such as the rim of an open box, is the exception: round it after the shell, because the shell can fail on it.

Verify

• Each stage: run measure {} (about 1 KB) and compare the volume, bbox and face count with your numbers. A cut or hole that leaves the volume unchanged has missed, even though it reported success.
• Timeline health: inspect_design {"measure":false,"sketches":false} shows each feature's error and warning.
• Parameter test: run set_parameter. Expect errors: [], then measure again; the COM and bbox should move by the amounts you computed.
• Positions: measure does not say where a feature sits.
  • On an asymmetric part, check the COM shift you computed.
  • On a symmetric part (a mirrored or patterned layout) the COM does not move, so take a top-view screenshot and compare distances in pixels against a known size.
  • body_topology is a last resort: it costs 25-45 KB and splits cylinders into half faces.
• Final look: one screenshot {"source":"model","view":"iso","width":480,"height":320}. Use "view":"top" for features inside walls, which the iso view hides.
  • width and height apply only to model renders.
  • When the server is bridged, source defaults to the whole app window and view also turns the user's camera, so pass "source":"model" and leave out view unless the user wants the camera moved.

Finish

export {path} writes .step for CAD, .3mf/.stl for printing, or .urdf (an assembly with joints, for robot simulators). save {path} writes .solidcraft.

Red flags

Thought	Do instead
"List all commands first"	reference.md, or list_commands {"filter":"<distinctive word>"}. The unfiltered list is over 100 KB.
"Check positions with body_topology"	measure COM and bbox against your numbers.
"Inspect the sketch"	sketch.solve returns dof and the profile count in under 100 bytes. Run sketch.inspect on its own, never inside a big batch.
"new_design for a clean start"	When the server is bridged, ask first.
"It reported ok, so it worked"	Only a measure that matches the computed values counts.