CharlZKP/fusion-needle3

Fusion Needle

Version 0.2.0

Fusion Needle is a fine-tune of Needle 3 by Cactus Compute for one job: turning one written modelling step ("Ø6 hole at (10, 0)") into tool calls for Autodesk Fusion. It is the model behind the Fusion Needle desktop app, which sends each call to Fusion through the MCP server that Fusion itself provides.

• Input: one feature in plain English, a one-line design state, and up to five tool schemas.
• Output: 0 to 4 tool calls from a catalogue of 47 narrow tools (JSON, constrained by the engine's grammar).
• Runs: on the CPU, through Cactus's needle engine. No cloud service is involved.
• Files: fusion-mcp-20L.cact (63.4 MB), fusion-mcp-8L.cact (27.4 MB)

What is new in 0.2.0

47 tools instead of 33. The 14 added tools cover requests that 0.1.0 could not answer:

• Whole shapes in one step: a box from width, depth and height; a cylinder from diameter and height.
• Holes without coordinates: a hole in the centre of a face; a hole in each corner at a given margin; bolt holes by size, M3 to M12, as a clearance, counterbore or countersink hole.
• Working on the body: split it in two, make copies in a row, set the thickness of a plate, scale it, rotate it, delete it, hide it, show it, give it a colour.
• "Extrude down" and "extrude from the bottom" now mean the negative direction.

What got worse

Adding tools cost accuracy on the old ones, and the model is now too eager to call a tool.

• On the 620 test cases that 0.1.0 was measured on, exact match fell from 75.0% to 70.6%.
• On the requests among them that must produce no call (off-topic, a required value missing, a negated request), 0.2.0 calls a tool anyway in 37.8% of cases; 0.1.0 did so in 29.1% and base Needle 3 in 31.1%.

If you only need the original 33 tools, 0.1.0 is the better model. It stays available under the tag v0.1.0. Whichever version you use, check each call before it runs. The desktop app does part of this for you: it holds back calls whose numbers are not written in your request, but it cannot catch every wrong choice of tool.

Credit: Needle 3 by Cactus Compute

This model is not a new architecture and was not trained from scratch. It is derived from Needle 3, the tool-calling model by Cactus Compute, and it only runs on their engine. All credit for the base model, its architecture, the .cact format and the inference engine goes to them.

• Base model and engine: huggingface.co/Cactus-Compute/needle3
• Needle 3 release page: cactuscompute.com/needle
• Source and Python package (cactus-needle, Apache-2.0): github.com/cactus-compute/needle
• Documentation: Needle Python Docs, Fine-tuning Needle, How to Design Tools for Needle 3

This project is independent. It is not affiliated with, sponsored by or endorsed by Cactus Compute or by Autodesk, Inc. Autodesk and Fusion are registered trademarks or trademarks of Autodesk, Inc.

Intended use

Driving Autodesk Fusion step by step from a written feature list, with a person watching:

plate 40x30x10 → Ø6 hole at (10, 0) → polar pattern ×6 → fillet the top edges R2

The companion app splits the goal into features, asks the model for the calls of one feature at a time, shows them, and runs vetted script templates in Fusion. The model never writes code.

Not intended for: general chat, free-form CAD scripting, tools outside the catalogue below, or unattended use on designs that matter.

Tools

The model was tuned for these 47 tools. Their full JSON schemas are in tools.json.

Tool	Family	What it does	Arguments (required in bold)
create_sketch	sketch	Start a new sketch on an origin plane or on a face of the body.	plane, face, offset
draw_rectangle	sketch	Draw a rectangle in the active sketch, centred on a point.	width, height, center_x, center_y
draw_circle	sketch	Draw a circle in the active sketch.	diameter, center_x, center_y
draw_line	sketch	Draw a straight line in the active sketch between two points.	start_x, start_y, end_x, end_y
draw_slot	sketch	Draw a straight slot (obround) in the active sketch; 20x6 = length 20, width 6.	length, width, center_x, center_y, angle
add_dimension	sketch	Add a driving dimension to entities of the active sketch.	kind, value, entity_one, entity_two
add_constraint	sketch	Add a geometric constraint between entities of the active sketch.	kind, entity_one, entity_two
extrude	feature	Extrude (pad) the active sketch profile into a solid, or cut it out of the body (pocket).	distance, operation, direction, extent
create_hole	feature	Drill a hole into a face of the body.	diameter, x, y, depth, face
circular_pattern	feature	Repeat a feature or body around an axis (polar pattern, circular array).	count, axis, angle, target
rectangular_pattern	feature	Repeat a feature or body in a row or grid along X and Y (linear pattern).	x_count, x_spacing, y_count, y_spacing, target
mirror	feature	Mirror a feature or body across an origin plane.	plane, target
fillet	feature	Round edges of the body with a radius.	radius, edges
chamfer	feature	Bevel edges of the body with an equal-distance chamfer.	distance, edges
shell	feature	Hollow out the body, leaving walls of a given thickness and one face open.	thickness, open_face
undo	history	Undo the most recent operation.
redo	history	Redo the most recently undone operation.
draw_polygon	sketch	Draw a regular polygon such as a hexagon in the active sketch.	shape, size, measure, center_x, center_y, angle
draw_arc	sketch	Draw a circular arc in the active sketch, counter-clockwise from a start to an end angle.	radius, start_angle, end_angle, center_x, center_y
revolve	feature	Revolve the active sketch profile around an origin axis into a solid (turned part).	axis, angle, operation
combine	body	Boolean of bodies: join the other bodies to the first body, subtract them from it, or keep the overlap.	operation
move_body	body	Move the body by a distance along X, Y and Z.	x, y, z
set_material	body	Assign a physical material to the body.	material
set_parameter	parameter	Create a named user parameter or change its value.	name, value, unit
list_parameters	parameter	List the user parameters with their values.
measure_body	inspect	Report the size (bounding box), volume and mass of each body.
check_timeline	inspect	Check the timeline for features with errors or warnings.
capture_view	view	Take a screenshot of the model, optionally from a standard view direction.	direction
fit_view	view	Zoom the view so the whole model fits the window.
export_model	document	Export the design to a file in a named format.	format, name
new_document	document	Create a new empty design document.
save_document	document	Save the active document.
open_document	document	Find a saved document by name and open it.	name
create_box	body	Create a box (block, cube) in one step, centred on the origin.	width, depth, height
create_cylinder	body	Create a cylinder (rod, disc) in one step, standing on the origin.	diameter, height
center_hole	feature	Drill a hole at the centre (middle) of a face of the body.	diameter, depth, face
corner_holes	feature	Drill a hole near each corner of a face of the body.	diameter, margin, depth, face
bolt_hole	feature	Drill a clearance hole for a metric screw such as M6.	size, style, x, y
split_body	body	Split the body into two bodies at its middle (cut it in half).	direction, offset
copy_body	body	Duplicate the body: make copies of it in a row.	count, spacing, axis
set_thickness	feature	Change the thickness (height) of the existing body by editing its extrude.	thickness
scale_body	body	Scale the body uniformly by a factor (resize, make bigger or smaller).	factor
rotate_body	body	Rotate the body in place by an angle around an axis.	angle, axis
delete_body	body	Delete the body from the design.
hide_body	body	Hide the body (make it invisible) without deleting it.
show_body	body	Show hidden bodies again (unhide).
set_color	body	Give the body a colour (appearance).	color

How to use

With the app

Install Fusion Needle. It downloads manifest.json and the default weight file from this repository on its first start, checks the SHA-256, and works offline afterwards.

Directly, with the needle Python package

pip install cactus-needle==3.1.1
needle download CharlZKP/fusion-needle3/fusion-mcp-20L.cact --out .

import json
import needle

catalogue = json.load(open("tools.json", encoding="utf-8"))
offered = ["create_hole", "draw_circle", "extrude", "fillet", "undo"]          # at most five per turn
agent = needle.Needle(
    tools=[tool for tool in catalogue if tool["name"] in offered],
    system="units: mm; sketch: none; bodies: Body1; last_feature: Extrude1",    # facts about the design
    weights="fusion-mcp-20L.cact",
    auto_date=False,
)
answer = agent.complete("Ø6 hole at (10, 0)")
print(answer["function_calls"])
# expected shape: [{"name": "create_hole", "arguments": {"diameter": 6, "x": 10, "y": 0}}]

The weight files are tied to the engine version (cactus-needle==3.1.1). The system line is a list of facts in exactly this form: units, sketch (none or <name> on <plane>), bodies, last_feature.

Evaluation

Numbers are measured on the built weight files through the shipped engine, on a held-out suite of hand-written single-step requests (calls, multi-call steps and requests that must produce no call) that were never used for tuning. A case counts as exact only when the tool names and every argument match. The suite has 844 cases.

Metric	Fine-tuned, 20 layers	Base Needle 3
Exact match (right tools and right arguments)	67.8% (n=844)	49.4% (n=844)
Tool selection (right set of tools)	76.5%	59.2%
Argument accuracy (given the right tools)	84.8% (n=488)	74.5% (n=325)
False-call rate on requests that need no call (lower is better)	42.1% (n=273)	35.9% (n=273)
Missed-call rate on requests that need a call (lower is better)	5.9% (n=571)	32.8% (n=571)

Original cases and cases added in 0.2.0

The suite grew from 620 to 844 cases with this version. The 224 added cases cover the new tools and more requests that must produce no call. 0.1.0 has no figure for them because it does not have the new tools.

Cases	0.2.0 exact match	0.1.0 exact match	Base Needle 3 exact match	0.2.0 false calls	0.1.0 false calls	Base Needle 3 false calls
Original 620 cases	70.6%	75.0%	50.2%	37.8% (n=196)	29.1% (n=196)	31.1% (n=196)
224 cases added in 0.2.0	59.8%		47.3%	53.2% (n=77)		48.1% (n=77)
All 844	67.8%		49.4%	42.1% (n=273)		35.9% (n=273)

Against base Needle 3, the fine-tune is 18 points ahead on exact match, mostly because it calls a tool when one is needed (it misses about 6% of such requests, the base model about 33%). It is behind the base model at staying silent: it makes a call on 42.1% of the requests that need none, the base model on 35.9%. The added cases are harder than the original ones for both models.

All figures are for the 20-layer file. The 8-layer file has not been scored.

Limitations

• Values must be written in the request. The model copies argument values from the text. It does not convert units, compute, or guess: "make a hole" has no diameter, so the answer is no call.
• One feature per turn. A turn yields at most four calls and the model has no memory of earlier turns; the design state line is its only context.
• At most five tools are visible per turn. The app chooses them with a keyword router; a request whose tool is not among the five cannot be answered correctly.
• Millimetres and English. The tools take millimetres and the suite is English only.
• No confidence score. Locally tuned Needle models do not report one; rely on the empty answer and on the calls the engine withholds.
• Only lightly tried in a real Autodesk Fusion. The scores above compare the model's calls with expected calls. Whether every call produces the intended geometry in Fusion has been tried by hand for a handful of requests on Windows only; see the status section of the app's README.
• Only the 47 tools above. Lofts, sweeps, threads, drawings, CAM and assemblies are out of scope.

Files

File	Layers	Size	SHA-256
fusion-mcp-20L.cact	20	63.4 MB	b0da36c0f9515c4e809f3717c634c0d75a6926a82a9c001f8db0a2778b4dafbd
fusion-mcp-8L.cact	8	27.4 MB	b896dca4e603ed0d6695b5cda8f158f5cba5cec473acf26824eb20b4dd9d7776

manifest.json lists every weight file with its size and SHA-256; the app verifies a download against it.

Licence

Apache-2.0, the same licence as the Needle 3 base weights these are fine-tuned from. See LICENSE.