Discover the functions and capabilities of various sketch constraints in Fusion. This article delves into the workings of constraints such as coincident, collinear, concentric, midpoint, fix-unfix, parallel, and more, and how they can be applied to manipulate geometry in the software.
Key Insights
- Sketch constraints in Fusion are tools used to relate two pieces of geometry to each other, limiting their motion in relation to one another. They are shown on the sketch palette on the right of your screen under constraints.
- Each constraint has a unique function such as the coincident constraint which snaps one geometry onto another, the collinear constraint that places one line directly on top of another line, and the midpoint constraint which places one geometry at the midpoint of another geometry.
- Fusion automatically limits the constraints you can select based on the specific geometries selected. When selecting geometry, you can right-click to see which sketch constraints are available for that selection set.
In this video we will look at sketch constraints. You will see that I am in my sketch constraints file, and I am currently editing sketch 1. In Fusion, constraints are used to relate two pieces of geometry to each other.
They are not like dimensions because they do not use specific numbers for distances or angles, but rather they limit geometry's motion in relation to one another. You will see the constraints in your sketch palette on the right of your screen under constraints. The first constraint is the coincident constraint.
This constraint snaps one geometry onto another geometry. If I click the middle of this circle, and then I click this line, you will see my circle be moved onto the line. I'm hitting escape to stop my constraint, and now as I drag my circle, you can see that the circle cannot move off of the line.
If I go back to the coincident constraint, and select this circle, and then the point of this line, and again hit escape, you can see as I move the circle, the line now changes. Again, the circle cannot be moved off of the line, but the line will change length. Next is the collinear constraint.
This places one line directly on top of another line. I will select this edge of my rectangle, and then this line, and you will see my rectangle be moved onto that line. Next is the concentric constraint.
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This constraint places the center point of a circle or arc onto another center point of a circle or arc. I will select the constraint, select this circle, and then my arc. I'll do it again for this circle to this circle, and you can see I can still change the size of my circle, but I cannot move it because a concentric constraint has been applied.
Next is the midpoint constraint. This places one geometry at the midpoint of other geometry. I will select this point, and then select this line, and you will see the triangle appear next to my point, and it is now snapped at the midpoint of this line.
If I select this edge of my rectangle, and then this line, you will see the midpoint of my rectangular edge has been placed at the midpoint of this line. I can further place a collinear constraint to align my rectangle with my line. Let's go midpoint one more time, and I will select the endpoint of this line, and then anywhere along this line, and you can see that I can still edit my line, except for this end is snapped to the midpoint.
Next is fix-unfix. I will place a coincident constraint from this point to the edge of this circle. Notice that my circle can still be edited, and my line can still be edited.
I would like to move this point of my line, but keep my circle in place. I can go to fix-unfix, select my circle, and hit escape. Now as I edit my line, only this line can be edited, and the circle must stay in the same place.
I can always unfix my circle to allow it to move. Next is the parallel constraint. This places a parallel condition between two lines.
I will select this edge, and then this edge. This constraint is different from the collinear constraint because my lines do not have to be touching. Next is the perpendicular constraint.
This places one line perpendicular to another. I will select this line, and then this line, and again, this line is not connected to my rectangle, but I can place a coincident constraint to snap it to the edge. Next is the horizontal-vertical constraint.
For this constraint, when you select two objects, Fusion will decide if they are closer in the horizontal direction or the vertical direction, and will snap them horizontal or vertical. I'm going to go undo, and I'm going to first move this circle lower, and then go horizontal-vertical one more time. Again, I can move my objects around, but where my vertical and horizontal constraints have been applied, that limits their motion.
Next is the tangent constraint. You can place tangency between arcs, circles, and lines. I will go tangent from this line to this circle, and you can see that I can still edit my line.
And if I go tangent from this circle to my rectangle, because a midpoint constraint has been applied, both sides of my rectangle are now tangent. Next is the smooth constraint. I will go sketch, spline, and select this endpoint, and then this endpoint, and hit my green check mark.
And you can see that I can change my spline and try to line up my continuity with these lines. This can be difficult to do, so I will undo, go smooth, select my spline, and then this line, and then my spline, and this line. This creates continuity between this line and my spline all the way through.
Next is the equal constraint. The equal constraint places the same dimension on all geometry selected. You will see as I place equal constraints that my circles become the same size.
And as I change the size of one circle, all of the circles will update to that size. The last constraint is the symmetry constraint. This places symmetry about two pieces of geometry around a single axis line.
If I go midpoint and select this line and this edge of my rectangle, you can see as I drag the top of my rectangle, there is symmetry applied because this line is snapped to the midpoint. However, if I would like symmetry away from my rectangle, I can go symmetry, select the top and bottom of this rectangle, and then this midline. Now my rectangle has symmetry applied about the midpoint, but I can still move my rectangle around the screen.
Fusion understands which constraints can be applied between specific geometries and will limit the constraints you can select. If I pre-select my line and my circle, you will see that only fix-unfix and the tangent constraints are available. Selecting the tangent constraint will automatically put a tangency constraint between these two pieces of geometry.
If I select the inside of my circle and this line, we can see midpoint and equal are available. I will select midpoint and we can now see the center of my circle has been placed at the midpoint of that line. Also, when selecting geometry, you can right-click and see which sketch constraints are available for that selection set.
