Add Coincident



Constraints toolbar


Add menu > Geometry sub-menu> > Constraints sub-menu > Add Coincident

To add:

Click Add Coincident Constraint, then click:

two Lines (or: a Line and the X-axis or Y–axis)

- or -

a Point and a Line (or a Circle), (or a Point and the X-axis or Y–axis)

- or -

two Points

- or -

or a Point and a Motion-Point

To delete:

1.Click a sketch-element that is 'coincident' with a different sketch-element...

The sketch-element and the constraint show in the Selection-Window.

- or -

1.In the Geometry Tree, explore the 'Constraint Loops' to find the Coincident constraint
2.Click the Coincident constraint.

The Coincident constraint is now in the Selection-Window.

2.Right-click the Coincident constraint in the Selection-Window
3.Click 'Delete' in the contextual-menu


If the two sketch-elements have a total of more than two degrees-of-freedom:

the two Lines (or a Line and the X or Y–axis) become collinear

- or -

the Point becomes coincident with the 'ray' of the Line,
the Point becomes coincident with the circumference of the Circle

- or -

the two Points become coincident.

Note: If the two sketch-elements have a total of 1 degree-of-freedom, then the two sketch-elements cannot become 'coincident'.

In MechDesigner, you cannot remove more than two degrees-of-freedom from a Point. For example, you cannot do these two steps:

STEP 1: Add a Coincident Constraint between a Point and a Line (or axis) - this removes 1 degree-of-freedom from the Point.
STEP 2: Add a Coincident Constraint between the same Point and another Point - this attempts to remove a further 2 degrees-of-freedom - it CANNOT!


A Coincident Constraint between a Point and a Line removes 1 DOF from the Point.
A Coincident Constraint between a Point and a Point removes 2 DOF from the Point.

Thus, delete the constraint between the Point and the Line (STEP 1), before you add the constraint between the two Points (STEP 2).

About Point Symbols

'+' : centre-Points - at the centre of Arcs and Circles
'O' : start-Point or end-Point - at the end of a Line and Arc
CirclePlus : centre-Point that is coincident with a start-Point or end-Point.

You may need to select the '+' or the 'O' with a command, and it is important to see the difference between the two Points and be able to select one Point or the other Point.

When a centre-Point is Merged with a start-Point or end-Point of a Line or Arc, the symbol is a '+'. You cannot select one or the other, because there is only one Point.

Motion-Point : Motion-Point - added to a sketch-element with Add Motion-Path FB.
Motion-Point Point: Motion-Point coincident with a start-Point or end-Point.

See Also:

Merge-Points, Horizontal, Vertical

All About Sketch-Loops


Use Add Coincident between two Points for construction geometry.

Use Merge-Points for sketch-loops and sketch-paths.

Points that are 'coincident' give you the option to delete the Coincident Constraint later.

Coincident constraints in the Graphic-Area, Selection-Window and Geometry-Tree.




In Selection-Window &

Geometry-Tree as...

Geometry-coin-lines - b4

Geometry-coin-lines - af

Two Lines:
Line and X or Y–axis

The Lines become collinear


geometry-coin-ptol b41

geometry-coin-ptol af1

Point and Line (or X & Y–axis)
a.The Point lies on 'ray' of the Line.




b.A Point in a sketch-element and Line



c.The X or Y–axis or Ray of the X or Y–axis.

Geometry-coin-ptoc b4

Geometry-coin-ptoc af

Point and Circle:

The Point is constrained to lie on the circumference of a Circle


geometry-coin-ptop b41

geometry-coin-ptop af1

Point and Point:

The Points become coincident



Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd