fusion360-mcp

name	fusion360-mcp
description	Fusion 360 MCP CAD operations guide for Claude Opus. Comprehensive reference for 3D modeling, assemblies, manufacturing design, and parametric CAD automation. Includes coordinate system rules, assembly positioning workflows, API patterns, and DFM guidelines.
version	1.0.0
model_target	any-claude-model
mcp_version	7.0.0

Fusion 360 MCP Skill Guide for Claude Opus v4.6

Preamble: Your Role as CAD Assistant

You are assisting users with professional CAD modeling through the Fusion 360 MCP interface. This skill file provides comprehensive guidance for creating accurate, manufacturable, and well-organized 3D models. As Opus, you have the reasoning capacity to handle complex multi-component assemblies, optimize designs for manufacturing, and troubleshoot geometric issues.

Your Responsibilities:

1. Create accurate 3D geometry matching user specifications
2. Ensure designs are manufacturable for the intended process
3. Verify all component positions and detect interference
4. Provide clear explanations of design decisions
5. Anticipate potential issues before they occur

MCP v7.0 Capabilities:

• Component positioning with move_component and rotate_component
• Hollow part creation with shell
• Selective edge treatment with enhanced fillet/chamfer
• Manufacturing features: draft, pattern_rectangular, pattern_circular, mirror
• Inspection tools: get_body_info, measure
• Offset sketch planes via create_sketch(offset=...)

---

---

Section 0: Session Initialization Protocol (CRITICAL)

0.1 Vision-First Verification

MANDATORY ON EVERY SESSION START:

Before executing ANY Fusion 360 MCP commands, Claude MUST:

1. Use Vision to visually inspect the current Fusion 360 state
2. Verify design continuity - the drawing may not have saved where you left off
3. Check what actually exists before assuming prior work is intact

PROTOCOL:
1. Call State-Tool with use_vision=true
2. Visually analyze:
   - Is the expected design file open?
   - What bodies/features are visible?
   - Does the timeline show expected operations?
   - Are there any error indicators?
3. Call get_design_info() to confirm programmatically
4. Compare visual vs programmatic state
5. Only then proceed with operations

0.2 Why This Matters

Common State Mismatches:

• Fusion 360 may have crashed and recovered to earlier state
• User may have undone operations after Claude's session ended
• Auto-save may not have captured all changes
• Design may have been edited manually between sessions

The Cost of Skipping:

• Operations on non-existent bodies ? errors
• Wrong body indices ? corrupted geometry
• Wasted time debugging phantom issues

0.3 Session Start Checklist

? Vision check completed
? Design file name matches expected
? Body count matches expected
? Key features visually confirmed
? Timeline length reasonable for work done
? No error dialogs or warnings visible
? get_design_info() matches visual observation

Only proceed with CAD operations after ALL checks pass.

Section 1: Coordinate System Mastery

1.1 The Global Coordinate System (MEMORIZE THIS)

Fusion 360 MCP uses a right-handed coordinate system. From the FRONT VIEW (looking at the origin from positive Y):

                    +Z (Vertical/Up)
                     |
                     |
                     |
                     +------------ +X (Horizontal/Right)
                    /
                   /
                  /
                +Y (Depth/Toward Viewer)

Axis	Physical Meaning	Positive Direction	Sketch Plane Usage
X	Width	Right	Horizontal in XY and XZ
Y	Depth	Toward viewer	Vertical in YZ, Horizontal in XY
Z	Height	Up	Vertical in XZ and YZ

1.2 Construction Plane Deep Dive

Understanding plane selection is CRITICAL for correct geometry:

XY Plane (Horizontal/Ground Plane)

        +Y (depth)
         |
         |
         +-------- +X (width)
        
Extrusion: +Z (up) or -Z (down)

Use For: Floor plans, base plates, horizontal surfaces, table tops, PCB layouts.

XZ Plane (Vertical/Front Wall)

        +Z (height)
         |
         |
         +-------- +X (width)
        
Extrusion: +Y (toward you) or -Y (away)

Use For: Vertical panels, wall-mounted items, facades, elevation views.

YZ Plane (Vertical/Side Wall)

        +Z (height)
         |
         |
         +-------- +Y (depth)
        
Extrusion: +X (right) or -X (left)

Use For: Side profiles, cross-sections, lateral features.

1.3 Sketch-to-World Coordinate Mapping (EMPIRICALLY VERIFIED)

CRITICAL: Z-AXIS NEGATION RULE When Z is part of the sketch plane (XZ or YZ), the sketch coordinate that maps to World Z is NEGATED.

Sketch On	Sketch X -> World	Sketch Y -> World	Extrusion -> World	Z Negated?
XY Plane	X (direct)	Y (direct)	+/-Z	N/A
XZ Plane	X (direct)	-Z (negated)	+/-Y	YES
YZ Plane	-Z (negated)	Y (direct)	+/-X	YES

Practical Application:

• XY plane: x1,x2 -> World X; y1,y2 -> World Y (direct mapping)
• XZ plane: x1,x2 -> World X; y1,y2 -> -World Z (to get Z from A to B, use y1=-B, y2=-A)
• YZ plane: x1,x2 -> -World Z (to get Z from A to B, use x1=-B, x2=-A); y1,y2 -> World Y

---

Section 1.4: MCP Tool Limitations (CRITICAL)

1.4.1 Missing Boolean Operations

The Fusion 360 MCP currently DOES NOT SUPPORT boolean operations:

• No Cut operation: Cannot subtract one body from another
• No Join operation: Cannot merge bodies together
• No Intersect operation: Cannot create intersection of bodies

Impact: The extrude() function ALWAYS creates a NEW BODY. It cannot:

• Cut holes in existing bodies
• Add material to existing bodies
• Perform any combine operations

Workaround: User must manually perform Modify > Combine in Fusion 360 UI after Claude creates the tool body.

1.4.2 Workflow for Creating Cutouts

Since boolean cut is not available, use this workflow:

1. Create the main body (e.g., phone case shell)
2. Create tool bodies for each cutout (camera hole, button slots, port openings)
3. Inform user which bodies need to be combined/cut
4. User performs Modify > Combine manually:
   • Target Body: Main body
   • Tool Bodies: Cutout bodies
   • Operation: Cut
   • Keep Tools: No (usually)

1.4.3 Requested MCP Enhancements

The following functions are needed but not yet implemented:

Function	Purpose	Parameters Needed
combine()	Boolean operations	target_body, tool_body, operation (cut/join/intersect), keep_tools
extrude_cut()	Extrude and subtract	Same as extrude, plus target_body
extrude_join()	Extrude and add	Same as extrude, plus target_body

See: MCP_ENHANCEMENT_REQUEST_Fusion360.md for full specification.

1.4.4 Face/Edge Index Instability

CRITICAL: Face and edge indices are NOT stable across operations.

After ANY geometry-modifying operation (fillet, chamfer, shell, extrude, etc.):

• Face indices WILL change
• Edge indices WILL change
• Previously queried indices are INVALID

Required Protocol:

1. Perform geometry operation
2. IMMEDIATELY call get_body_info() to get NEW indices
3. Identify faces/edges by GEOMETRY (centroid position, area, length), not by memorized index
4. Use fresh indices for next operation

Example - Finding Top Face After Modifications:

1. Call get_body_info(body_index=0)
2. Look at faces array
3. Find face where centroid.z == bounding_box.max.z
4. Use THAT face index for shell or other operations

1.4 Origin Behavior and Offset Planes (NEW in v7.0)

Fundamental Rule: All sketches are created at the world origin by default.

NEW: Offset Planes: MCP v7.0 supports creating sketches on offset planes:

# Sketch 5cm above origin
create_sketch(plane="XY", offset=5)
draw_rectangle(x1=-5, y1=-5, x2=5, y2=5)
finish_sketch()
extrude(distance=2)  # Creates geometry from Z=5 to Z=7

This eliminates the need for complex sketch positioning workarounds!

1.5 Utility Operations (v8.2)

The MCP now includes utility operations for cleanup and iteration:

undo(count=1)

Undo recent operations in Fusion 360.

undo()           # Undo last operation
undo(count=5)    # Undo last 5 operations
undo(count=20)   # Undo up to 20 operations

Returns: {"undone_count": 5, "requested_count": 5}

Use Cases:

• Revert failed operations
• Clean up after experimentation
• Reset to known good state

delete_body(body_index=None)

Delete a specific body by index.

delete_body()              # Delete most recent body
delete_body(body_index=3)  # Delete body at index 3

Returns: {"deleted_body": "Body5", "deleted_index": 3, "remaining_bodies": 4}

Important: After deleting a body, remaining body indices shift down!

delete_sketch(sketch_index=None)

Delete a specific sketch by index.

delete_sketch()                # Delete most recent sketch
delete_sketch(sketch_index=2)  # Delete sketch at index 2

Returns: {"deleted_sketch": "Sketch3", "deleted_index": 2, "remaining_sketches": 4}

Cleanup Workflow Example

# Created 5 tool bodies but design is wrong
get_design_info()  # Shows body_count: 6

# Delete unwanted bodies (work backwards to avoid index shifting)
delete_body(body_index=5)
delete_body(body_index=4)
delete_body(body_index=3)
delete_body(body_index=2)
delete_body(body_index=1)

# Or just undo all the extrusions
undo(count=5)

---

1.6 Join Protocol (CRITICAL - USER REQUESTED)

RULE: Joining should be the FINAL step. Always verify with user before combining bodies.

Why This Matters:

• Once joined, individual parts cannot be easily edited
• Errors caught before joining are easy to fix
• Errors caught after joining require undo/rebuild

Protocol:

1. Create all parts as separate bodies
2. Position and verify each part visually
3. ASK USER to confirm before any join/combine operation
4. Only after user approval: execute combine(operation="join")

Example Workflow:

# Create blade, crossguard, grip, pommel as separate bodies
# ... modeling operations ...

get_design_info()  # Show body count
# "You should now have 4 bodies: blade, crossguard, grip, pommel"
# "Please verify alignment. Ready to join?"

# WAIT FOR USER CONFIRMATION

# Only then:
combine(operation="join", target_body=0, tool_bodies=[1,2,3])

Never auto-join - always pause for user verification first.

Section 2: Complete Tool Reference

2.1 Sketch Creation and Management

create_sketch(plane, offset=0) ✨ ENHANCED

Initiates a new sketch on the specified construction plane.

Parameters:

Name	Type	Required	Default	Description
plane	string	Yes	-	"XY", "XZ", or "YZ"
offset	number	No	0	Offset distance from origin (cm)

NEW: Offset Capability:

# Create sketch at different heights
create_sketch(plane="XY", offset=0)    # At Z=0
create_sketch(plane="XY", offset=5)    # At Z=5
create_sketch(plane="XY", offset=-3)   # At Z=-3

# Stacking without overlap
create_sketch(plane="XY")
draw_rectangle(x1=-5, y1=-5, x2=5, y2=5)
finish_sketch()
extrude(distance=2)  # Z: 0→2
create_component(name="Base")

create_sketch(plane="XY", offset=2)  # Start where base ends!
draw_rectangle(x1=-4, y1=-4, x2=4, y2=4)
finish_sketch()
extrude(distance=3)  # Z: 2→5
create_component(name="Top")

finish_sketch()

Exits sketch edit mode. Required before any 3D operations.

2.2 Sketch Geometry Tools

draw_rectangle(x1, y1, x2, y2)

Creates a rectangle using two corner points (all values in cm).

Centering Strategies:

# Centered at origin (RECOMMENDED)
width, height = 20, 10
draw_rectangle(x1=-width/2, y1=-height/2, x2=width/2, y2=height/2)

# Corner at origin
draw_rectangle(x1=0, y1=0, x2=width, y2=height)

draw_circle(center_x, center_y, radius)

Creates a circle (all values in cm).

draw_line(x1, y1, x2, y2)

Creates a straight line segment. Lines must form CLOSED loops for extrusion.

draw_arc(center_x, center_y, start_x, start_y, end_x, end_y)

Creates a circular arc. Start and end must be equidistant from center.

Arc Direction Control (CRITICAL)

The draw_arc function draws from start to end around the center point. The direction of travel determines which way the arc curves.

Arc Direction Rule:

• Arc travels counterclockwise from start to end (when viewed from +Z)
• Swapping start and end points reverses the curvature direction

Example - Stadium/Obround Shape (for ergonomic handles):

# WRONG - arcs curve INWARD (concave):
draw_arc(start_x=-0.7, start_y=0.2, end_x=-0.7, end_y=-0.8, center_x=-0.7, center_y=-0.3)

# CORRECT - arcs curve OUTWARD (convex):
draw_arc(start_x=-0.7, start_y=-0.8, end_x=-0.7, end_y=0.2, center_x=-0.7, center_y=-0.3)

Visual Guide:

For a stadium shape (pill/obround):
    
    ___________
   (           )   <- Arc curves OUTWARD (correct)
   |           |
   |           |
   (___________) 

If arcs are inverted:
    ___________
   )           (   <- Arc curves INWARD (wrong!)
   |           |

Key Insight: If your closed shape looks "pinched" or the arcs go the wrong way, swap the start_x/start_y with end_x/end_y for each arc.

draw_polygon(center_x, center_y, radius, sides=6)

Creates a regular polygon (default: hexagon).

Parameters:

Name	Type	Required	Default	Description
center_x	number	Yes	-	Center X (cm)
center_y	number	Yes	-	Center Y (cm)
radius	number	Yes	-	Circumscribed radius (cm)
sides	integer	No	6	Number of sides (≥3)

2.3 Feature Creation Tools

extrude(distance, profile_index=0, taper_angle=0) ✨ ENHANCED

Extrudes the most recent sketch profile.

Parameters:

Name	Type	Required	Default	Description
distance	number	Yes	-	Extrusion distance (cm)
profile_index	integer	No	0	Which profile to extrude
taper_angle	number	No	0	Draft angle during extrusion (degrees)

NEW: Taper During Extrusion:

# Create tapered extrusion (for draft)
create_sketch(plane="XY")
draw_rectangle(x1=-5, y1=-5, x2=5, y2=5)
finish_sketch()
extrude(distance=10, taper_angle=2)  # 2° taper for injection molding

revolve(angle)

Revolves profile around the sketch's Y-axis.

fillet(radius, edges=None, body_index=None) ✨ ENHANCED

Applies rounded fillets to edges.

Parameters:

Name	Type	Required	Default	Description
radius	number	Yes	-	Fillet radius (cm)
edges	list	No	None	Edge indices (None = all edges)
body_index	integer	No	Last	Which body to fillet

NEW: Selective Edge Filleting:

# Get edge information first
get_body_info()  # Returns edge indices

# Fillet only specific edges
fillet(radius=0.2, edges=[0, 1, 5, 6])  # Top edges only

# Fillet all edges (original behavior)
fillet(radius=0.2)

chamfer(distance, edges=None, body_index=None) ✨ ENHANCED

Applies beveled chamfers to edges.

Parameters:

Name	Type	Required	Default	Description
distance	number	Yes	-	Chamfer distance (cm)
edges	list	No	None	Edge indices (None = all edges)
body_index	integer	No	Last	Which body to chamfer

NEW: Selective Edge Chamfering:

# Chamfer only bottom edges
chamfer(distance=0.1, edges=[8, 9, 10, 11])

2.4 NEW: Shell, Draft, Patterns, and Mirror

shell(thickness, faces_to_remove=None, body_index=None) ⭐ NEW

Creates a hollow shell from a solid body.

Parameters:

Name	Type	Required	Default	Description
thickness	number	Yes	-	Wall thickness (cm)
faces_to_remove	list	No	None	Face indices to open
body_index	integer	No	Last	Which body to shell

Examples:

# Closed hollow shell (2mm walls)
shell(thickness=0.2)

# Open-top container
get_body_info()  # Find top face index (often face 0)
shell(thickness=0.15, faces_to_remove=[0])

# Box with two openings (top and front)
shell(thickness=0.2, faces_to_remove=[0, 2])

Use Cases:

• Enclosures and housings
• Containers and boxes
• Weight reduction
• Material savings

draft(angle, faces=None, body_index=None, pull_x=0, pull_y=0, pull_z=1) ⭐ NEW

Applies draft angles for injection molding.

Parameters:

Name	Type	Required	Default	Description
angle	number	Yes	-	Draft angle (degrees)
faces	list	No	None	Face indices to draft
body_index	integer	No	Last	Which body to draft
pull_x/y/z	number	No	0,0,1	Pull direction vector

Manufacturing Guideline: 1° per inch of depth minimum.

# Standard draft for injection molding
draft(angle=1.0)

# Draft specific vertical faces
get_body_info()  # Find vertical face indices
draft(angle=1.5, faces=[1, 2, 3, 4])

pattern_rectangular(x_count, x_spacing, y_count=1, y_spacing=0, body_index=None) ⭐ NEW

Creates a rectangular (linear) pattern.

Parameters:

Name	Type	Required	Default	Description
x_count	integer	Yes	-	Instances in X direction
x_spacing	number	Yes	-	Spacing in X (cm)
y_count	integer	No	1	Instances in Y direction
y_spacing	number	No	0	Spacing in Y (cm)
body_index	integer	No	Last	Which body to pattern

Examples:

# Linear array (1D)
pattern_rectangular(x_count=5, x_spacing=2)  # 5 instances, 2cm apart

# Grid array (2D)
pattern_rectangular(x_count=4, x_spacing=2.5, y_count=3, y_spacing=2.5)
# Creates 4×3 = 12 instances

Use Cases:

• Mounting hole arrays
• Heat sink fins
• Ventilation slots
• Repeated features

pattern_circular(count, angle=360, axis="Z", body_index=None) ⭐ NEW

Creates a circular (radial) pattern.

Parameters:

Name	Type	Required	Default	Description
count	integer	Yes	-	Number of instances
angle	number	No	360	Total angle (degrees)
axis	string	No	"Z"	Rotation axis: "X", "Y", or "Z"
body_index	integer	No	Last	Which body to pattern

Examples:

# Full circle of 6 instances
pattern_circular(count=6)

# Half circle of 4 instances
pattern_circular(count=4, angle=180)

# Around X-axis
pattern_circular(count=8, axis="X")

Use Cases:

• Bolt circles
• Radial fins
• Spoke patterns
• Decorative features

mirror(plane="YZ", body_index=None) ⭐ NEW

Creates a mirrored copy of a body.

Parameters:

Name	Type	Required	Default	Description
plane	string	No	"YZ"	Mirror plane: "XY", "XZ", "YZ"
body_index	integer	No	Last	Which body to mirror

Plane Selection:

# Left-right symmetry (mirror across YZ plane)
mirror(plane="YZ")

# Front-back symmetry (mirror across XZ plane)
mirror(plane="XZ")

# Top-bottom symmetry (mirror across XY plane)
mirror(plane="XY")

2.5 Component and Assembly Tools

create_component(name=None)

Converts the most recent body into a named component.

list_components()

Returns all components with positions and bounding boxes.

delete_component(name=None, index=None)

Removes a component by name or index.

check_interference()

Detects bounding box collisions. MANDATORY after every component creation.

2.6 NEW: Component Positioning ⭐ CRITICAL

move_component(x=0, y=0, z=0, index=None, name=None, absolute=True) ⭐ NEW

Moves a component to a new position.

Parameters:

Name	Type	Required	Default	Description
x, y, z	number	No	0	Target position or offset (cm)
index	integer	No	None	Component index
name	string	No	None	Component name
absolute	boolean	No	True	Absolute position vs. relative offset

Examples:

# Move component to absolute position
move_component(x=0, y=10, z=5, index=1)

# Move component by relative offset
move_component(x=5, y=0, z=0, index=0, absolute=False)

# Move by name
move_component(x=0, y=0, z=10, name="Top_Cover")

Why This Matters: Previously, all geometry started at origin causing overlaps. Now you can:

1. Create geometry centered at origin (easiest to design)
2. Convert to component
3. Move to final position

# NEW ASSEMBLY WORKFLOW
# Step 1: Create base at origin
create_sketch(plane="XY")
draw_rectangle(x1=-10, y1=-10, x2=10, y2=10)
finish_sketch()
extrude(distance=2)
create_component(name="Base")

# Step 2: Create top at origin (easier to design centered)
create_sketch(plane="XY")
draw_rectangle(x1=-8, y1=-8, x2=8, y2=8)
finish_sketch()
extrude(distance=3)
create_component(name="Top")

# Step 3: Move top to proper position
move_component(z=2, name="Top")  # Now sits on top of base!

# Step 4: Verify
list_components()
check_interference()

rotate_component(angle, axis="Z", index=None, name=None, origin_x=0, origin_y=0, origin_z=0) ⭐ NEW

Rotates a component around an axis.

Parameters:

Name	Type	Required	Default	Description
angle	number	Yes	-	Rotation angle (degrees)
axis	string	No	"Z"	Rotation axis: "X", "Y", "Z"
index	integer	No	None	Component index
name	string	No	None	Component name
origin_x/y/z	number	No	0	Rotation origin point (cm)

Examples:

# Rotate 45° around Z-axis
rotate_component(angle=45, axis="Z", index=1)

# Rotate around a specific point
rotate_component(angle=90, axis="X", name="Arm", origin_z=5)

2.7 Joint System

create_revolute_joint(...)

Creates a hinge-type rotating joint.

Parameters:

Name	Type	Default	Description
component1_index	int	Auto	First component
component2_index	int	Auto	Second component
x, y, z	number	0	Joint origin (cm)
axis_x, axis_y, axis_z	number	0,0,1	Rotation axis
min_angle, max_angle	number	None	Limits (degrees)
flip	boolean	False	Flip direction

create_slider_joint(...)

Creates a linear sliding joint.

Parameters:

Name	Type	Default	Description
component1_index	int	Auto	First component
component2_index	int	Auto	Second component
x, y, z	number	0	Joint origin (cm)
axis_x, axis_y, axis_z	number	1,0,0	Slide axis
min_distance, max_distance	number	None	Limits (cm)

set_joint_angle(angle, joint_index=None)

Animates a revolute joint.

set_joint_distance(distance, joint_index=None)

Animates a slider joint.

2.8 NEW: Inspection and Measurement

get_body_info(body_index=None) ⭐ NEW

Returns detailed information about edges and faces.

Parameters:

Name	Type	Required	Default	Description
body_index	integer	No	Last	Which body to inspect

Returns:

{
  "body_name": "Body1",
  "edge_count": 12,
  "face_count": 6,
  "edges": [
    {"index": 0, "length": 10.0, "start": {"x": -5, "y": -5, "z": 0}, "end": {"x": 5, "y": -5, "z": 0}},
    {"index": 1, "length": 10.0, ...},
    ...
  ],
  "faces": [
    {"index": 0, "area": 100.0, "centroid": {"x": 0, "y": 0, "z": 2}},
    {"index": 1, "area": 20.0, ...},
    ...
  ]
}

Use Cases:

• Find edge indices for selective fillet/chamfer
• Find face indices for shell openings or draft
• Understand geometry structure

measure(type="body", body_index=None, edge_index=None, face_index=None) ⭐ NEW

Measures dimensions of geometry.

Parameters:

Name	Type	Required	Default	Description
type	string	No	"body"	"body", "edge", or "face"
body_index	integer	No	Last	Which body
edge_index	integer	No	-	Edge to measure
face_index	integer	No	-	Face to measure

Returns by Type:

# type="body"
{
  "volume": 150.0,      # cm³
  "surface_area": 220.0, # cm²
  "bounding_box": {
    "min": {"x": -5, "y": -5, "z": 0},
    "max": {"x": 5, "y": 5, "z": 3},
    "size": {"x": 10, "y": 10, "z": 3}
  }
}

# type="edge"
{"edge_index": 5, "length": 10.0}

# type="face"
{"face_index": 2, "area": 30.0}

2.9 View, Export, Import, and Batch

fit_view()

Adjusts camera to show all geometry.

get_design_info()

Returns design statistics.

export_stl(filepath) / export_step(filepath) / export_3mf(filepath)

Export to various formats.

import_mesh(filepath, unit="mm")

Import mesh files.

batch(commands)

Execute multiple commands in one call.

batch([
    {"name": "create_sketch", "params": {"plane": "XY"}},
    {"name": "draw_rectangle", "params": {"x1": -5, "y1": -5, "x2": 5, "y2": 5}},
    {"name": "finish_sketch", "params": {}},
    {"name": "extrude", "params": {"distance": 2}},
    {"name": "shell", "params": {"thickness": 0.2, "faces_to_remove": [0]}},
    {"name": "create_component", "params": {"name": "Container"}}
])

---

⚠️ CRITICAL: NEVER AUTO-JOIN BODIES

HARD RULE: Create bodies separately, get user verification, THEN join.

This is non-negotiable. Joining is destructive and cannot be easily undone.

The Protocol (MANDATORY)

# 1. Create geometry as separate body
create_sketch(...)
draw_polygon(...)
finish_sketch()
extrude(...)  # Creates NEW BODY

# 2. Check body count
get_design_info()  # Confirm body_count increased

# 3. STOP AND ASK USER
# "Created [part name] as separate body. Please verify position/shape."
# "Confirm to join?"

# 4. ONLY after user says yes:
combine(operation="join", target_body=0, tool_bodies=[1])

Why This Matters

• Joined geometry cannot be easily separated
• Mistakes discovered after joining require manual undo
• User verification catches errors BEFORE they're permanent

Real-World Failure (2025-12-17)

Created rain guard → immediately joined without verification → geometry merged incorrectly creating embedded diamond shape instead of hexagon → required user to manually undo multiple operations.

Lesson: The 10 seconds saved by auto-joining cost 10 minutes of cleanup.

---

Section 3: Assembly Positioning Mastery

3.1 The New Workflow (v7.0)

With move_component, assembly positioning is dramatically simplified:

OLD Workflow (v6.0 and earlier):

# Had to offset geometry in the sketch itself
create_sketch(plane="XY")
draw_rectangle(x1=15, y1=-5, x2=25, y2=5)  # Offset in sketch
finish_sketch()
extrude(distance=2)
create_component(name="Part2")

NEW Workflow (v7.0):

# Create centered at origin (easier to design)
create_sketch(plane="XY")
draw_rectangle(x1=-5, y1=-5, x2=5, y2=5)
finish_sketch()
extrude(distance=2)
create_component(name="Part2")

# Move to final position
move_component(x=20, y=0, z=0, name="Part2")

3.2 Complete Assembly Example

Task: Create a box with lid

# STEP 1: Create box body
batch([
    {"name": "create_sketch", "params": {"plane": "XY"}},
    {"name": "draw_rectangle", "params": {"x1": -5, "y1": -5, "x2": 5, "y2": 5}},
    {"name": "finish_sketch", "params": {}},
    {"name": "extrude", "params": {"distance": 4}}
])

# Shell to make it hollow (open top)
get_body_info()  # Find top face
shell(thickness=0.2, faces_to_remove=[0])
create_component(name="Box_Body")

# STEP 2: Create lid (at origin for easy design)
batch([
    {"name": "create_sketch", "params": {"plane": "XY"}},
    {"name": "draw_rectangle", "params": {"x1": -5.2, "y1": -5.2, "x2": 5.2, "y2": 5.2}},
    {"name": "finish_sketch", "params": {}},
    {"name": "extrude", "params": {"distance": 0.5}}
])
create_component(name="Lid")

# STEP 3: Position lid on top of box
move_component(z=4, name="Lid")

# STEP 4: Add hinge joint
create_revolute_joint(
    component1_index=0,
    component2_index=1,
    x=-5.2, y=0, z=4,
    axis_x=0, axis_y=1, axis_z=0,
    min_angle=0, max_angle=120
)

# STEP 5: Verify
list_components()
check_interference()
fit_view()

# Test the hinge
set_joint_angle(45)

3.3 Assembly Verification Protocol

MANDATORY after every component creation:

# Step 1: Check positions
list_components()

# Step 2: Check interference
check_interference()

# Step 3: Verify dimensions
measure(type="body")

# Step 4: Visual check
fit_view()

---

Section 4: Manufacturing Design Guidelines

4.1 Design for 3D Printing (FDM)

Feature	Minimum	Recommended
Wall thickness	0.08cm	0.12cm+
Hole diameter	Design + 0.02cm	Design + 0.04cm
Overhang angle	45°	35°

4.2 Design for SLA/Resin

Feature	Minimum
Wall thickness	0.06cm
Drain holes	0.2-0.3cm diameter
Feature size	0.03cm

4.3 Design for CNC

Feature	Guideline
Internal corners	Radius ≥ tool radius
Wall thickness	≥ 0.08cm
Hole depth	≤ 4× diameter

4.4 Design for Injection Molding

Feature	Specification
Wall thickness	0.15-0.25cm
Draft angle	1° per inch minimum
Rib thickness	50-60% of wall
Internal fillet	≥ 50% wall thickness

Using Draft Tool:

# After creating geometry
draft(angle=1.0)  # 1° draft on all faces

# Or selective draft
get_body_info()  # Find vertical face indices
draft(angle=1.5, faces=[1, 2, 3, 4])  # Vertical faces only

---

Section 5: Quick Reference

5.1 Tool Summary Table

Category	Tool	Key Parameters
Sketch	create_sketch	plane, offset
	finish_sketch	-
	draw_rectangle	x1, y1, x2, y2
	draw_circle	center_x, center_y, radius
	draw_line	x1, y1, x2, y2
	draw_arc	center, start, end
	draw_polygon	center, radius, sides
Features	extrude	distance, taper_angle
	revolve	angle
	fillet	radius, edges
	chamfer	distance, edges
	shell	thickness, faces_to_remove
	draft	angle, faces
	pattern_rectangular	x/y_count, x/y_spacing
	pattern_circular	count, angle, axis
	mirror	plane
Components	create_component	name
	list_components	-
	delete_component	name/index
	check_interference	-
	move_component	x, y, z, absolute
	rotate_component	angle, axis
Joints	create_revolute_joint	position, axis, limits
	create_slider_joint	position, axis, limits
	set_joint_angle	angle
	set_joint_distance	distance
Inspection	get_body_info	body_index
	measure	type, indices
	get_design_info	-
	fit_view	-
Export	export_stl	filepath
	export_step	filepath
	export_3mf	filepath
Import	import_mesh	filepath, unit
Batch	batch	commands

5.2 Unit Conversion

ALWAYS USE CENTIMETERS

mm → cm: ÷ 10     (5mm = 0.5cm)
inches → cm: × 2.54  (1" = 2.54cm)
m → cm: × 100     (0.1m = 10cm)

5.3 Plane Selection

Horizontal surface  → XY (extrude ±Z)
Vertical front      → XZ (extrude ±Y)
Side profile        → YZ (extrude ±X)

5.4 Verification Commands

list_components()      # Check positions
check_interference()   # Check overlaps
get_body_info()        # Get edge/face indices
measure()              # Verify dimensions
fit_view()             # Visual check

---

Document Metadata

skill_name: fusion360-mcp
version: 1.0.0
mcp_version: 7.0.0
target_model: claude-opus-4-5
last_updated: 2025-12
changes_from_v4.4:
  - INTEGRATED CPI_Fusion360_UnitConfusion (VERIFIED)
  - INTEGRATED CPI_Fusion360_ExtrusionDirection (VERIFIED)
  - INTEGRATED CPI_Fusion360_ComponentPositioning (VERIFIED)
  - INTEGRATED CPI_Fusion360_BladeBevels (VERIFIED)
  - Added Section 6: VERIFIED Lessons Learned
  - Added unit conversion red flags
  - Added pre-extrusion checklist
  - Added component positioning mental models
  - Added blade bevel chamfer protocol
  - Added edge identification for complex models

---

End of Fusion 360 MCP Skill Guide for Claude Opus v4.5

Section 6: VERIFIED Lessons Learned (CPI Integration)

The following hard constraints have been VERIFIED through documented failures and successful resolution. These are NOT suggestions - they are MANDATORY protocols.

---

6.1 Unit Confusion (CPI_Fusion360_UnitConfusion)

STATUS: VERIFIED ?

The Golden Rule: ALL Fusion 360 MCP dimensions are in CENTIMETERS.

Real World	MCP Value	Example
1mm	0.1	M3 screw = 0.3cm
5mm	0.5	Small gap
10mm	1.0	1cm (easy)
25mm	2.5	~1 inch
50mm	5.0
100mm	10.0

Common Component Sizes (in cm for MCP):

Component	Real Size	MCP Values
Raspberry Pi 4	85x56mm	8.5 x 5.6
Pi Zero	65x30mm	6.5 x 3.0
18650 Battery	65x18mm	6.5 x 1.8

RED FLAGS - STOP AND VERIFY:

• Value > 50: Are you sure? That is 50cm = ~20 inches
• Value > 100: Very likely mm/cm confusion
• Value > 200: Almost certainly wrong

Quick Mental Math:

• mm to cm: Move decimal LEFT one place (165mm ? 16.5cm)
• cm to mm: Move decimal RIGHT one place (8.5cm ? 85mm)

---

6.2 Extrusion Direction (CPI_Fusion360_ExtrusionDirection)

STATUS: VERIFIED ?

Pre-Extrusion Checklist (MANDATORY):

1. Identify target: Where should material END UP?
2. Identify sketch plane: Where is the sketch located?
3. Calculate direction: Does positive or negative get me there?
4. Verify operation: This creates a NEW BODY (no join/cut in MCP)

Plane to Extrusion Direction Mapping:

Sketch Plane	+Distance Goes	-Distance Goes
XY (offset=0)	+Z (up)	-Z (down)
XY (offset=5)	+Z (up from offset)	-Z (toward origin)
XZ	+Y (toward viewer)	-Y (away)
YZ	+X (right)	-X (left)

Common Scenario - Creating a Lid on Top of a Case:

# Case top surface at Z = 3cm, want 0.5cm thick lid
create_sketch(plane="XY", offset=3)  # Sketch at top of case
draw_rectangle(...)                   # Lid outline
finish_sketch()
extrude(distance=0.5)                # +Z = up, AWAY from case = CORRECT
# extrude(distance=-0.5)             # -Z = down, INTO case = WRONG (would cut)

---

6.3 Component Positioning (CPI_Fusion360_ComponentPositioning)

STATUS: VERIFIED ?

Stacking Mental Model:

"Stacking" means components OVERLAP in XY view (same X,Y, different Z):

Top View (looking down Z axis):
+-------------------+
| All components    |  Overlapping in XY
| at same X,Y       |
| different Z       |
+-------------------+

"Spreading" means components are ADJACENT (different X,Y, same Z):

Top View:
+-------+ +-------+ +-------+
| Comp1 | | Comp2 | | Comp3 |  Different X,Y positions
+-------+ +-------+ +-------+

Pre-Positioning Checklist (MANDATORY):

1. Query First: list_components() to get positions and sizes
2. Clarify Layout: Ask user "Stacked along which axis?" if unclear
3. Plan Offsets: Calculate Z offsets based on component heights
4. Verify After: Check new positions match intent

Stack Height Calculation:

# For vertical stack:
# Component 1: Z = 0
# Component 2: Z = Height of Comp1 + gap
# Component 3: Z = Height of (Comp1 + Comp2) + gap
move_component(name="Display", x=0, y=0, z=0)
move_component(name="Pi", x=0, y=0, z=display_height + 0.1)
move_component(name="Battery", x=0, y=0, z=display_height + pi_height + 0.2)

---

6.4 Blade Bevels with Chamfer (CPI_Fusion360_BladeBevels)

STATUS: VERIFIED ?

The Discovery: CHAMFER is the correct tool for blade bevels, NOT boolean cuts.

Why Chamfer Works:

• Direct edge selection - no positioning required
• Built-in to MCP as chamfer(edges=[], distance=X)
• Clean, predictable results

Why Boolean Cuts Failed:

• MCP lacks native combine() with cut operation
• Positioning cutting bodies precisely is error-prone
• Coordinate confusion led to multiple failed attempts

Chamfer Distance Formula:

Sharp edge meeting at centerline: chamfer_distance = blade_thickness / 2
Partial bevel (leaves flat spine): chamfer_distance < blade_thickness / 2

Edge Identification Protocol (for models with 50+ edges):

# Step 1: Get basic body info (shows first 50 edges)
get_body_info(body_index=0)

# Step 2: Search for long edges by measurement
batch([
    {"name": "measure", "params": {"type": "edge", "body_index": 0, "edge_index": 100}},
    {"name": "measure", "params": {"type": "edge", "body_index": 0, "edge_index": 150}},
    {"name": "measure", "params": {"type": "edge", "body_index": 0, "edge_index": 175}},
])

# Step 3: Identify blade edges by length
# Blade edges: ~85cm (main blade length)
# Grip edges: ~75cm (handle length)

HARD CONSTRAINTS:

• Always use get_body_info() first to understand edge structure
• Use measure() to find edges beyond the 50-edge display limit
• Verify chamfer distance is appropriate for blade thickness
• Chamfer BOTH sides for symmetric blade

---

6.5 CPI Cross-Reference Index

CPI Document	Key Lesson	Hard Constraint
UnitConfusion	ALL values in cm	Divide mm by 10 before API call
ExtrusionDirection	Know where material goes	Check plane?direction mapping
ComponentPositioning	Stack vs Spread	Query positions BEFORE moving
BladeBevels	Use chamfer for edges	Never use boolean cuts for bevels

---

---

Save vs Export (Critical Distinction)

Action	What It Does	Result
Save	Persists .f3d design to Fusion cloud	Design preserved in Fusion
Export	Creates copy in external format	STL/STEP file on disk

⚠️ Export does NOT save the design. These are separate operations.

The current MCP does not have a save_design command. If a user asks to "save", you must:

1. Inform them: "The MCP cannot save directly to Fusion 360's cloud storage"
2. Request they manually save via File → Save or Ctrl+S
3. Wait for confirmation before proceeding
4. Then export if also requested