What is the ʼCoincidentʼ constraint in Autodesk Fusion?
Short Answer
The Coincident constraint in Autodesk Fusion makes a sketch point lie exactly on another point, line, arc, or curve using Coincident. It is the most common professional method for attaching endpoints and locking sketch intent during 2D sketching. Limitation: it only controls position contact, not size, angle, or tangent behavior.
What You Need to Know Before
Warning: Coincident can overconstrain a sketch if the point already has dimensions or conflicting constraints such as Fix, Horizontal/Vertical, or Tangent. A common failure is selecting the entire curve instead of the intended endpoint, which changes the sketch behavior unexpectedly.
How to Apply the Coincident Constraint
Command: Coincident
Shortcut: None by default
Quick Steps:
- Start or edit a sketch, then go to the Sketch Ribbon > Constraints panel > Coincident.
- Click the sketch point you want to attach, usually an endpoint or center point.
- Click the target geometry such as another point, edge, line, arc, or spline, then confirm the constraint glyph appears.
Use the fastest professional method: apply Coincident directly while sketching or immediately after creating geometry to fully define connections early.
Variables & Settings
Key Setting: Show Constraints toggle in the Sketch Palette
Expert Setting: Turn on Show Constraints to verify that the Coincident glyph was actually applied to the correct point and not a nearby object. This is the quickest way to diagnose missed or stacked constraints in dense sketches.
Why it Fails
Cause 1 (Geometry): You selected a line or curve body instead of the actual endpoint, so the point snaps onto the object but not to the intended location.
Cause 2 (layers/Locks): Projected geometry or fixed sketch geometry may already be constrained, preventing the point from moving into the required coincident position.
Cause 3 (Command/Logic): The sketch already has conflicting dimensions or constraints, so adding Coincident creates an overconstrained condition.
Quick Fix & Best Practice
Quick Fix: Use Show Constraints in the Sketch Palette, delete the conflicting constraint or dimension, then reapply Coincident by selecting the movable point first and the target geometry second.
Manager’s Verdict: Use Coincident as the default method for connecting sketch geometry because it is fast, stable, and easy to audit. Avoid stacking it blindly on fully constrained sketches without checking existing dimensions and projected references.
FAQ
Is Coincident the same as Merge in Fusion?
No, Coincident constrains location in a sketch, while Merge behavior depends on the specific tool or context.
Can Coincident be applied to projected edges?
Yes, but projected geometry may already be constrained and can limit movement.
Does Coincident fully define a sketch?
No, it only controls positional contact and usually must be combined with dimensions or other constraints.
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