Sketch constraints are a fantastic way to ensure accuracy in your sketching. Through constraints you can ensure something is on the midpoint, is perfectly concentric, won’t move from a line and more. Constraints are perfect for designing functional pieces for 3D printing.
To add a constraint, you'll need to select the sketch objects you want to constrain and press the corresponding constraint on the menu. Sometimes the order you select the objects in will affect how the constraint is applied.
Sketches can become over-constrained; this is where a constraint you want to apply would conflict with the rest of the constraints/dimensions on the sketch object. Sadly, Fusion doesn't help much when trying to figure out what is going wrong, often the best option is to check every constraint and see if they are necessary. You'll also want to double check which constraint you’re actually applying, some of them do look similar and do similar things so if in doubt double check.
If you want your sketch geometry to intersect each other and not let go, then you'll want to use the coincident constraint. You'll be able to move the joined geometry but not separate them.
Sketch geometry that is collinear shares a ‘common line’. This constraint works well for keeping sketch geometry lined up even when moved.
The concentric constraint will make two or more circles/arcs share a common centre point. This is perfect for nesting circles and arcs within each other.
As the name implies this constraint forces one sketch object to be at the centre point of another sketch object. This is an extremely useful constraint, especially when resizing your sketches.
This constraint will cause lines to stay parallel to each other.
This constraint will force two sketch objects to remain at a 90-degree angle to each other.
This constraint simply constrains a line or points to go on or remain on the vertical or horizontal axis.
The tangent constraint is perfect for connecting a curve to a line smoothly since it will force the curve and line to touch at a point but not cross. This helps the line look like it continues into the curve or vice versa.
This constraint used to be called the smooth constraint and it creates a smooth curve between objects. It’s a bit tricky and you’re unlikely to apply this one manually.
If you want parts of your sketch to be exactly equal then this constraint will prove to be very helpful. This constraint will force any sketch geometry, of the same kind, to be perfectly equal to each other.
Often this constraint is automatically applied when you use mirror in the create menu. When applied manually, you’ll select two pieces of sketch geometry and provide a symmetry line. When mirroring you can remove the symmetry constraint afterwards to allow sketch geometry to be more easily edited.
Fix and Unfix
If you want to stop parts of your sketch from being changed, moved, edited or transformed in any way then you'll want to fix it. Once fixed, the object will go green. To unfix the object simply select it and press the fix/unfix constraint again. You'll find that imported SVGs will come in fixed.