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04 Sketching

2D Sketching & Constraints

Learn the foundation of all CAD: drawing perfectly constrained 2D profiles using exact mathematical rules.

Beginner ~10 min

The Sketch Environment

Every 3D feature starts with a flat 2D drawing. You first pick a starting plane — either one of the three standard reference planes (XY, XZ, or YZ, each formed by a pair of the X/Y/Z axes) or a flat face on a solid you've already built.

The Golden Rule of Sketching
  • Start at the Origin: Always anchor your first line or circle to the exact center origin (0,0,0).
  • Keep it Simple: One sketch should define one feature. Do not draw every detail of the part in a single mega-sketch.
  • Close the Loop: A sketch must form a completely closed profile to be turned into a solid.
1 Experience
2 Reflect
3 Theorize
4 Apply

Geometric Constraints

Constraints are strict mathematical rules that force geometry to behave. They are more robust than physical dimensions.

∥
Parallel / Perpendicular

Forces two lines to never intersect, or to intersect at exactly 90 degrees.

◎
Concentric

Forces two arcs or circles to share the exact same center point.

⚯
Tangent / Coincident

Forces a line to perfectly graze a circle, or locks two points exactly together.

Dimensions & The Constraint Color Code

Blue vs. Black Lines
Color Meaning Action Required
Blue Under-constrained The line can still be dragged. Add dimensions or constraints!
(Black) Fully Constrained The shape is locked down. Ready to be made 3D.
Red / Yellow Over-constrained Conflicting rules applied. Delete the duplicate dimension.

Never extrude a blue (under-constrained) sketch. If lines can still be dragged around, your 3D feature will shift the moment someone edits an upstream dimension.

Pause and Reflect
✓ Your reflections are saved automatically
Apply What You Learned

Launch your CAD software and sketch a generic motor mounting plate.

  • Select the Top Plane (XY) and snap your first line/rectangle to the Origin
  • Draw a large circle for the motor shaft to pass through
  • Draw four smaller bolt holes and make them Equal size using constraints
  • Make the bolt holes Concentric or aligned exactly to the center shaft hole
  • Add strict Dimensions until every single line turns Black (Fully Constrained)
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