Constraints

Define geometric relationships in Print CAD — coincident, distance, tangent, parallel, perpendicular, symmetric, angle, and more.

Constraints are the foundation of parametric design in Print CAD. Instead of drawing geometry at fixed positions, you define relationships between entities — two points are coincident, two lines are parallel, a distance equals a variable. When you change a variable or drag a point, the constraint solver recalculates all geometry to maintain every relationship simultaneously.

Print CAD supports over 40 constraint types. The most commonly used for packaging dieline design are listed below.

Applying Constraints

Select one or more entities in the graphics window.
Open the Constraint menu and choose the constraint type, or use the keyboard shortcut.
The constraint appears as an annotation on the canvas. Click the annotation to edit its value.

Constraints are color-coded:

Satisfied constraints display in the default color
Unsolved or conflicting constraints are highlighted, indicating the solver cannot find a solution

To remove a constraint, select its annotation and press Delete.

Dimensional Constraints

Constraint	Entities	Description
Distance	Two points, or point and line	Sets the exact distance between entities. Accept a numeric value or a variable name. This is the primary constraint for parametric dimensions.
Angle	Two lines	Sets the angle between two line segments in degrees.
Diameter	Circle or arc	Sets the diameter of a circle or arc.
Length Ratio	Two lines	Constrains one line's length to be a ratio of another's.
Length Difference	Two lines	Constrains the difference between two line lengths to a specific value.

Geometric Constraints

Constraint	Entities	Description
Coincident	Two points	Forces two points to occupy the same position. Essential for connecting line endpoints to form closed shapes.
Horizontal	Line, or two points	Constrains a line segment or point pair to be horizontal (parallel to the X axis).
Vertical	Line, or two points	Constrains a line segment or point pair to be vertical (parallel to the Y axis).
Parallel	Two lines	Forces two lines to be parallel regardless of their position.
Perpendicular	Two lines	Forces two lines to meet at a 90-degree angle. Critical for box dielines where panels meet at right angles.
Equal Length	Two lines	Forces two line segments to have the same length. Use this to keep symmetric panels equal without assigning the same variable to both.
Symmetric	Two points and a line	Forces two points to be mirror images across a line of symmetry. Useful for centering flaps and tabs.
Tangent	Arc/circle and line	Forces a curve and a line to meet tangentially (smooth transition, no corner).
Midpoint	Point and line	Constrains a point to lie at the exact midpoint of a line segment.
On Entity	Point and line/arc/circle	Constrains a point to lie on a curve or line.

Orientation Constraints

Constraint	Entities	Description
Lock Where Dragged	One or more points	Fixes selected points at their current position. PrintNow extension: supports locking multiple points simultaneously via the context menu.
Same Orientation	Two normals	Forces two workplane normals to point in the same direction.

Using Variables in Constraints

Any dimensional constraint (Distance, Angle, Diameter) can reference a variable or expression instead of a fixed number. Click the constraint annotation and type the variable name or expression:

W — Use the variable W directly
W / 2 — Half the width
W + 0.5 — Width plus a half-inch allowance
min(W, L) — The smaller of width and length

This is what makes the design parametric — the geometry adapts automatically when variable values change.

The Constraint Solver

Print CAD's solver handles up to 2,048 simultaneous unknowns using Eigen-based linear algebra. When you add or modify constraints:

Green/satisfied — The solver found a solution satisfying all constraints
Red/unsolved — The system is over-constrained (too many constraints) or inconsistent (contradictory constraints)
Under-constrained — Geometry has degrees of freedom remaining; drag points to see what can still move

If the solver fails, remove the most recently added constraint and check for conflicts. The property browser lists all constraints with their status.

Variables — Create the named values referenced in dimensional constraints
Expression System — Use formulas and functions inside constraint values
Line Styles — Assign structural purpose (cut, crease, perf) to constrained geometry
Quick Start — Apply constraints step-by-step in your first dieline