Troubleshooting Sketches

Overview#

Sketch problems fall into a small number of families: a profile that won't form, a solver that complains about constraints, geometry that behaves unpredictably, references that break, and interface or performance glitches. This page walks through each family with symptoms, causes, and fixes. Autodesk's help does not quote Fusion's warning messages, so the messages described here are paraphrases.

Where to find it#

There is no single command. The tools you will use:

• Sketch Palette: the sketch Status line, Find Under-Constrained, Compute Sketch, and the Show Profile, Show Points, Show Constraints, Show Dimensions and Show Projected Geometries toggles.
• Constraint badges and the Delete key.
• The timeline: a yellow warning on a sketch signals a lost projection link (right-click the sketch > Manage Lost Projections); right-click also offers Edit Sketch.
• Undo (Ctrl+Z) and version history.
• Measuring tools for checking small gaps (general guidance).

Problem 1: the profile will not shade or Extrude finds nothing#

Symptoms. You finish the sketch but the region is not blue-shaded. Extrude does not offer a profile to click, or highlights an unexpected area.

Causes and fixes.

1. Gap in the loop. The most common cause. Two endpoints are near but not coincident. Turn on Show Points and look for lone endpoints: unconstrained end points of lines and splines show as white dots, while joined point-to-point coincident points show no dot. Zoom far in on corners. Fix by dragging one endpoint onto the other, or apply Coincident. For a gap between two lines, Extend may close it.
2. Overlapping or duplicate segments. Two lines on top of each other, or a line overlapping an edge of a rectangle, confuse profile detection. Select by dragging a window and compare counts; delete duplicates. Use Trim to remove overlap.
3. Self-intersecting loop. A line crossing itself (like a figure eight) forms two profiles or none. Trim to the intersection.
4. Construction linetype. Construction geometry is not included in the boundaries of the sketch. Select the segment and click Construction next to Linetype in the Sketch Palette (or Normal/Construction in the marking menu) to switch it back.
5. Show Profile off. The region is closed but not shaded. Turn on Show Profile in the Sketch Palette.
6. Open spline or text artifact. Splines with end points a hair off a line, or imported artwork with micro gaps, are classic. Re-constrain the ends with Coincident.
7. Not coplanar. Geometry brought in as 3D sketch geometry (Include 3D Geometry) may not form flat profiles with 2D curves unless it lies in the sketch plane (general behavior). Use Project instead.

Quick test. Turn on Show Profile and look for the blue shading of closed profiles. If a region is not shaded, the loop is open somewhere.

Problem 2: over-constrained or conflicting constraints#

Symptoms. The new constraint or dimension conflicts with existing ones, or the sketch will not solve after an edit.

Note: not confirmed in Autodesk's documentation: the exact over-constraint dialog or the color a conflicting dimension takes. Check what your build shows.

Causes and fixes.

1. Redundant dimension. You dimensioned something the sketch already determined (for example the fourth side of a fully constrained rectangle with Equal opposites). Make the new dimension a driven dimension (right-click > Toggle Driven), or delete a constraint that makes it redundant.
2. Contradictory pair. Horizontal on a line and a 30 degree angle to the X axis cannot both hold. Delete one.
3. Fixed geometry plus dimensions. A Fixed item cannot satisfy a dimension that implies movement. Unfix it, or drop the dimension.
4. Projected geometry plus dimensions. Projected geometry has a defined position. Dimensioning two projected points to one another conflicts if the numbers disagree with the source. Make it driven.
5. Edit made it impossible. A new dimension value is geometrically impossible (a 100 mm line between points 50 mm apart in a rigid chain). Undo, then adjust the other end of the chain first.

Procedure. Undo the last action. Show Constraints. Identify the constraint or dimension that caused the conflict. Delete the least meaningful one. Reapply in a sensible order: anchor, relationships, dimensions.

Problem 3: geometry flips, jumps, or collapses#

Symptoms. After changing a dimension, a circle jumps to the other side of a line, an arc inverts, or a line collapses to zero length.

Causes and fixes.

• Ambiguous solutions. Tangents, angles, and arcs have multiple valid solutions; the solver picks the nearest to the previous position. A big dimension jump can land on the wrong one. Change the dimension in smaller increments, or drag the geometry near the desired solution first.
• Under-defined geometry. Free geometry can move as the solver wishes. Fully constrain the neighbors.
• Angle dimensions on the wrong side. Re-place the angle dimension on the side you intend, or use Perpendicular or Parallel in place of an angle.
• Zero-length segments. Setting a dimension to 0 collapses geometry. Never dimension a line to zero.
• Fillets larger than the edge. If a radius is larger than the adjacent lines can support, the fillet fails or flips. Reduce the radius.

Problem 4: broken projection or missing reference#

Symptoms. Projected geometry disappears, the sketch shows a warning icon in the timeline, features after it show errors, or the plane of the sketch is lost.

Causes and fixes.

1. Source edge or face changed. An upstream feature was edited so that the original edge no longer exists. A yellow warning appears on the sketch in the Timeline and the affected projected geometry is highlighted orange or yellow. Right-click the sketch and choose Manage Lost Projections, select the lost item, and choose Re-Link (pick a new body, face, edge or point), Break Link (keep it as non-associative geometry) or Delete Geometry. Delete All and Break Link All handle everything at once.
2. Source deleted or suppressed. Restore the feature, or redirect the sketch to another reference.
3. Sketch plane lost. When a sketch's plane is removed by a modification, you can redefine it; Autodesk covers this in the "Redefine a sketch plane" video, and the menu command name is not given in the written help.
4. Timeline order. You moved a sketch before the feature it depends on. Drag it back later in the timeline.
5. Cascading failures. Fix the earliest error first; later ones often clear automatically.

To avoid recurrence, see the best practices page: reference origin planes and stable sketches wherever possible.

Problem 5: dragging does not work or geometry will not move#

• Fully constrained geometry cannot be dragged. That is the point. Change a dimension or delete a constraint.
• Fixed geometry turns green; select the Fix/UnFix tool again and click the geometry to release it.
• Projected geometry is locked by default. To make it independent, project with Projection Link unchecked, or break the link (Manage Lost Projections > Break Link).

Problem 6: interface and display issues#

Problem 7: slow or unstable sketches#

• Too many constraints or splines in one sketch. Split into multiple sketches.
• Imported DXF or SVG with thousands of segments. Simplify in a vector editor or delete unneeded curves.
• Circular references. Dimensions that reference parameters that depend on each other can fail. Check the Parameters dialog for errors.
• Memory or graphics issues. General guidance: update graphics drivers and close other heavy programs.

Options reference: diagnostic toolbox#

Tips and pitfalls#

Tip: When in doubt, undo. A problem right after your last action usually points to the cause.

Tip: To find a gap quickly, box-select the whole sketch, then use Show Points; unpaired endpoints stand out. Alternatively drag-select a suspect corner and look at the selection count.

Tip: Use the timeline rollback bar to move before the broken feature, fix the earliest error, then roll forward.

Warning: Do not ignore warnings. A yellow warning on a sketch in the Timeline means a projection link is lost.

Warning: Do not delete conflicting constraints blindly; read what each does first.

Warning: Do not mask a gap with a tiny line. Make the end points coincident.

Practice exercise#

1. Draw a rectangle with lines, deliberately leaving a 0.01 mm gap at one corner. Notice the missing shading.
2. Use Show Points to find the gap and close it with Coincident. Confirm the profile now shades.
3. Dimension all four sides of the rectangle, and observe what happens on the last one; make it driven (right-click > Toggle Driven) if it conflicts.
4. Create a circle tangent to a line with a dimension, change the dimension drastically, and observe any flip. Repeat in small steps.
5. Project an edge from a body, change or delete the feature that made it, and look for the yellow warning on the sketch in the Timeline. Open Manage Lost Projections, then undo.

Expected result: you can find and fix a gap, resolve an over-constraint, and recover a lost projection.

Related#

• Constraints (02-sketching/constraints)
• Fully constrained sketches (02-sketching/fully-constrained-sketches)
• Project and include geometry (02-sketching/project-and-include)
• Sketch best practices (02-sketching/sketch-best-practices)