Fusion 360 Add-In · Arroway Ltd
RFX Equation to Sketch
Drive Fusion 360 sketches with math.
One command tucked into Sketch → Create: Equation Curve draws parametric splines from independent X(t), Y(t), and Z(t) expressions and polar splines from r(θ) — complete with named parameters that flow into Fusion's own Parameters dialog.
What's inside
Everything you need, nothing you don't.
Equation to Sketch is a focused tool. It adds a single command and gets out of your way.
Equation Curve
Sketch any curve you can express mathematically. Parametric mode gives you independent X(t), Y(t), and Z(t) expressions — ideal for helices, Lissajous figures, and 3D paths. Polar mode takes r(θ) for rose curves, spirals, and cardioids.
- ① Mode selector Parametric gives X(t), Y(t), Z(t) inputs — good for helices, Lissajous figures, and 3D space curves. Polar gives a single r(θ) input — good for spirals, rose curves, and cardioids.
- ② X(t) expression Any combination of t, named params, and whitelisted math functions. Use Z(t)=0 to stay flat.
- ③ Y(t) expression Expression for the Y coordinate at each sample point.
- ④ Z(t) expression Non-zero Z creates a 3D curve. For a flat sketch curve keep this at 0.
- ⑤ Parameters block Named values (e.g. r=20) become Fusion user parameters with the
eq_prefix, visible in the Parameters dialog and usable to drive model dimensions. - ⑥ t range Curve parameter range. Full circle: 0 to 2*pi. Half-arc: 0 to pi.
- ⑦ Sample points Number of points the spline passes through. 20–80 for most curves; 200–400 for high-frequency waves. Over 400 auto-splits into two segments.
- ⑧ Closed curve Joins the last sample back to the first. Use for closed loops; leave unchecked for open paths.
- t range with configurable start and end
- 2–400 sample points; auto-splits above 400
- Closed curve option connects last point to first
- Palette stays open for rapid iteration
- Warns when no active sketch is open
Safe Expression Evaluator
Equation to Sketch never calls eval(), exec(), or compile().
Expressions are parsed with ast.parse() then validated through a strict
two-layer whitelist before a single value is computed.
- Layer 1: any expression with
__rejected before AST construction - Layer 2: AST walker permits only literals, operators, and whitelisted functions
- Blocked: attribute access, keyword args, import / exec / eval / open / getattr
- Dry-run at t=0 catches expression errors eagerly, before Fusion's spline builder runs
Named Parameters → User Params
Any named variable in your expression — A, k, pitch
— becomes a Fusion 360 user parameter with an eq_ prefix. Change the value
in Fusion's Parameters dialog and update the curve without re-opening Equation to Sketch.
- Parameters appear in Fusion's Parameters dialog
- Can drive sketch dimensions and other features
- Registered on first curve insert in the session
- Every named constant in a curve expression is captured
Curve type reference
Parametric vs. Polar
Choose the mode that matches how you think about the shape.
| Mode | Inputs | Good for | Example |
|---|---|---|---|
| Parametric 2D | X(t), Y(t) | Ellipses, Lissajous figures, cam profiles, any closed or open planar path | X = a·cos(t) Y = b·sin(t) |
| Parametric 3D | X(t), Y(t), Z(t) | Helices, spirals, 3D sweep paths, spring profiles | X = r·cos(t) Y = r·sin(t) Z = pitch·t/(2·pi) |
| Polar | r(θ) | Rose curves, Archimedean spirals, cardioids, limaçons | r = A·cos(k·θ) |
Available math functions
sincostanasinacos atanatan2sinhcoshtanh degreesradians sqrtexploglog10 abshypotfloorceilround minmax pitauet Operators
Standard arithmetic: + - * / ** (power) % (modulo) // (floor division).
Unary minus is supported. No bitwise operators, no comparisons.
Installation
Three steps from the App Store to your sketch.
Equation to Sketch is available on the Autodesk App Store. Autodesk handles download and installation automatically — no folders to unzip, no scripts to run.
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Get it on the Autodesk App Store
Click the button below (or search RFX Equation to Sketch on the Autodesk App Store) and complete the purchase. A Fusion 360 subscription is required.
[Get RFX Equation to Sketch on App Store] -
Autodesk installs it automatically
The App Store pushes the add-in directly into Fusion 360. Restart Fusion if prompted. No manual folder selection or manifest setup required.
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Find the command
Equation Curve appears under Sketch → Create. Open or activate a sketch, then launch it to start drawing parametric or polar curves.
Usage tips
Get the most out of Equation to Sketch.
Open a sketch first
Equation Curve requires an active sketch. Create or double-click into a sketch before launching the palette.
Iterate without closing
The palette stays open after each insert. Adjust your expressions and click Insert again — great for tuning a shape interactively.
Name your constants
Use A = 30 in your expression rather than a raw number. Equation to Sketch registers eq_A in Fusion's Parameters — change it later without reopening the palette.
Tune sample count deliberately
Higher sample counts produce smoother curves but slow Fusion's spline builder. For display models try 80–120; for precision paths go up to 300. Equation to Sketch auto-splits above 400.
Troubleshooting
Common questions & known issues.
"No active sketch" warning when opening Equation Curve
Equation Curve must be launched from inside an active sketch. In the browser, double-click an existing sketch to activate it — or go to Sketch → Create Sketch and pick a plane — then open Equation Curve again.
Spline looks faceted or choppy
Increase the sample count. The default is intentionally conservative to keep Fusion responsive. For smooth curves on screen, try 120–200 points; for high-precision manufacturing paths, 300–400.
Inserting a curve is very slow
Very high sample counts (above ~300) push Fusion's spline builder hard. If you need more than 400 points, Equation to Sketch automatically splits the curve into two connected segments — but even then, expect a longer build time. If speed matters more than smoothness, reduce the count and use a lower t range step.
The Parameters dialog shows no eq_ parameters
Named parameters are registered on first insert, not when you open the palette.
Insert a curve with at least one named constant and the eq_ parameters
will appear in Fusion's Parameters dialog immediately after.
Ready to sketch with equations?
Available on the Autodesk App Store. Requires Fusion 360. Python runtime is bundled with Fusion — no extra setup.