Gear

What the source does

• FilesystemNone observedNo reads or writes in the source
• NetworkNone observedNo outbound calls in the source
• ShellNone observedNo commands run in the source
• DependenciesPinnedNothing floats
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass.

Audit 0.4.1 · source sha 24034f36bad7 · 19 Oct 2026Report an issue or request a re-scan

• Publisherghbalf GitHub userOwner of the repository this skill is read from
• Source folderghbalf/freecad-ai/skills/gearThe exact folder we audited
• LicenceLGPL-2.1As the repository states it
• Commit pinned for this verdict24034f36bad7A new audit runs when the source changes
• Repository statusNot archivedLast push 2 days ago
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its description: Create an involute spur gear using FreeCAD's Part module.

---
name: gear
description: "Create an involute spur gear using FreeCAD's Part module."
---

# Spur Gear Generator

Create an involute spur gear using FreeCAD's Part module.

## Parameters to extract from user request
- **Module** (m): tooth size parameter, default 2.0mm
- **Number of teeth** (z): default 20
- **Pressure angle**: default 20 degrees
- **Face width** (thickness): default 10mm
- **Bore diameter**: center hole, default 5mm (0 = no bore)

## Derived dimensions
- Pitch diameter: d = m * z
- Tip diameter: da = m * (z + 2)
- Root diameter: df = m * (z - 2.5)

## Construction

Use `execute_code` with the complete gear generation code below.
Replace the parameter values at the top with the user's requested values.

```python
import math
import Part
import FreeCAD as App

# === PARAMETERS (replace with user values) ===
module = 2.0
teeth = 20
pressure_angle_deg = 20
face_width = 10.0
bore_dia = 5.0

# === DERIVED ===
pitch_r = module * teeth / 2.0
base_r = pitch_r * math.cos(math.radians(pressure_angle_deg))
tip_r = pitch_r + module
root_r = pitch_r - 1.25 * module

def involute_pts(base_r, tip_r, n=20):
    max_angle = math.sqrt((tip_r / base_r) ** 2 - 1)
    pts = []
    for i in range(n):
        t = i * max_angle / (n - 1)
        x = base_r * (math.cos(t) + t * math.sin(t))
        y = base_r * (math.sin(t) - t * math.cos(t))
        pts.append(App.Vector(x, y, 0))
    return pts

def rotate_pt(pt, angle_rad):
    c, s = math.cos(angle_rad), math.sin(angle_rad)
    return App.Vector(c * pt.x - s * pt.y, s * pt.x + c * pt.y, 0)

def pt_angle(pt):
    return math.atan2(pt.y, pt.x)

# Involute half-tooth thickness angle
inv_alpha = math.tan(math.radians(pressure_angle_deg)) - math.radians(pressure_angle_deg)
half_thick_angle = math.pi / (2 * teeth) + inv_alpha

# Generate involute profile for one tooth, centered on +Y axis
right_involute = involute_pts(base_r, tip_r, 20)
right_side = [rotate_pt(p, -half_thick_angle + math.pi / 2) for p in right_involute]
left_side = [App.Vector(-p.x, p.y, 0) for p in right_side]

# Key points
left_base, left_tip = left_side[0], left_side[-1]
right_base, right_tip = right_side[0], right_side[-1]
lb_a, rb_a = pt_angle(left_base), pt_angle(right_base)

# Points on root circle at flank angles
lb_on_root = App.Vector(root_r * math.cos(lb_a), root_r * math.sin(lb_a), 0)
rb_on_root = App.Vector(root_r * math.cos(rb_a), root_r * math.sin(rb_a), 0)

# Build closed tooth profile: root → left involute → tip arc → right involute → root arc
tooth_edges = []

# Radial: left root → left base
if lb_on_root.distanceToPoint(left_base) > 0.01:
    tooth_edges.append(Part.LineSegment(lb_on_root, left_base).toShape())

# Left involute BSpline (base → tip)
bs_left = Part.BSplineCurve()
bs_left.interpolate(left_side)
tooth_edges.append(bs_left.toShape())

# Tip arc (left tip → right tip)
tip_mid_a = (pt_angle(left_tip) + pt_angle(right_tip)) / 2
tip_mid = App.Vector(tip_r * math.cos(tip_mid_a), tip_r * math.sin(tip_mid_a), 0)
tooth_edges.append(Part.Arc(left_tip, tip_mid, right_tip).toShape())

# Right involute BSpline (tip → base)
bs_right = Part.BSplineCurve()
bs_right.interpolate(list(reversed(right_side)))
tooth_edges.append(bs_right.toShape())

# Radial: right base → right root
if right_base.distanceToPoint(rb_on_root) > 0.01:
    tooth_edges.append(Part.LineSegment(right_base, rb_on_root).toShape())

# Root arc (right root → left root, closing the profile)
root_mid_a = (lb_a + rb_a) / 2
root_mid = App.Vector(root_r * math.cos(root_mid_a), root_r * math.sin(root_mid_a), 0)
tooth_edges.append(Part.Arc(rb_on_root, root_mid, lb_on_root).toShape())

# Create one tooth solid
tooth_wire = Part.Wire(tooth_edges)
tooth_face = Part.Face(tooth_wire)
tooth_solid = tooth_face.extrude(App.Vector(0, 0, face_width))

# Build gear: base cylinder + all teeth fused together
gear = Part.makeCylinder(root_r, face_width)
for t in range(teeth):
    rotated = tooth_solid.copy()
    if t > 0:
        rotated.rotate(App.Vector(0, 0, 0), App.Vector(0, 0, 1), t * 360.0 / teeth)
    gear = gear.fuse(rotated)
gear = gear.removeSplitter()

# Cut bore hole
if bore_dia > 0:
    bore = Part.makeCylinder(bore_dia / 2, face_width + 2, App.Vector(0, 0, -1))
    gear = gear.cut(bore)

# Add to document
gear_obj = App.ActiveDocument.addObject("Part::Feature", "Gear_M{}_Z{}".format(module, teeth))
gear_obj.Label = "Gear M{} Z{}".format(module, teeth)
gear_obj.Shape = gear
App.ActiveDocument.recompute()

print("Gear created: pitch dia={:.1f}mm, tip dia={:.1f}mm, root dia={:.1f}mm".format(
    pitch_r * 2, tip_r * 2, root_r * 2))
```

## Important
- Copy the COMPLETE code block above into `execute_code`, only changing the parameter values at the top
- Do NOT try to use PartDesign Body/Sketch for the gear — use Part::Feature directly
- Do NOT use `App.Gui` — it may not be available in the sandbox
- Label the gear clearly with its parameters: "Gear M2 Z24"
- The gear is centered at the origin

Excerpt, first 4,966 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

git clone https://github.com/ghbalf/freecad-ai
git -C freecad-ai checkout 24034f36bad7

Works in

1. 2026-10-19
   ✓SAFE B 89 / 100

   first audit · source 24034f36bad7

Questions about Gear

• github.com/ghbalf/freecad-ai/tree/master/skills/gear — the audited source at commit 24034f36bad7 and every finding aboveObserved · 19 Oct 2026

Spotted something wrong? Report a correction · Methodology