We want to join the Part to the Base-Part with a Pin-Joint. To do this, we need a Point in the Base-Part. However, we will add a Line to the Base-Part. In time, we will see why a Line in the Base-Part is more flexible than a Point.

Objective of this Step:

Learn how to start and close the Part-Editor.
Learn how to add and delete geometric elements: sketch-elements, dimensions and constraints in the Part-Editor.
Learn that some dimensions are negative - it is a MechDesigner Rule!
Learn that Black sketch-elements are fully-defined, and Blue sketch-elements are not fully-defined.

Summary of this Tutorial:

1.Start the Part-Editor to edit the Base-Part.
2.Add a Line sketch-element to the Base-Part .
3.Add Dimensions and Constraints to define the Line in the Base-Part.
4.Optionally, delete a Constraint, and add it again.
5.Close the Part-Editor to return to the Mechanism-Editor.



Tutorial 1: STEP 1.3

Add Line to Base-Part


Step by Step:

Edit the BasePart with the Part-Editor


To edit the Base-Part:

STEP 1: Double-Click the Green, rectangular, Part-Outline of the Base-Part

There are many different ways to start the Part-Editor.

See also: How to Start the Part-Editor


Use the Part-Editor to add, edit or delete 'Part Geometry. Part Geometry includes: sketch-elements, and the constraints and dimensions that you add to and between sketch-elements.

When the Part-Editor is active:

The Part-Outline goes out of view
The small axes change to the large axesRed-14-1b
The Mechanism name-tab changes to Part name-tabRed-14-2
The Kinematic-elements toolbar is not available, the Geometry toolbarRed-14-3 becomes available.
The Mechanism pointer changes to the Edit-Part pointerRed-14-4
The Part-Editor icon is toggled inRed-14-5

Add a Line to the Base-Part


Now, add a Line to the Base-Part:

STEP 2: Expand the Geometry toolbar
STEP 3: Click Geometry toolbar > Add Line Red-14-1b


Your pointer changes to the Add Line pointer.

STEP 4: Drag in the graphic-area to add a Line

The drag technique for Add Line is identical to that for Add Part

Note: Drag technique : Mouse-button down...move your mouse-pointer...mouse-button up:

A Line shows in the Part-Editor.

Now you need to locate the Line in the Base-Part with dimensions and constraints.

Add Coincident Constraints to the Line


Expand the Sketch-Constraints toolbar to the RIGHT of the graphic-area.

STEP 1: Click Sketch-Constraints toolbar > Add Coincident Constraint

Your pointer changes to the Add Coincident-Constraint

WE must click two elements to add a Coincident Constraint.


STEP 2: Click the PointRed-14-2 that is near to the X-axis
STEP 3: Click the X-axisRed-14-3


If you miss the second element you must click the two elements again.

The Point snaps to the X-axis.

Optionally Drag the Point along the X-axis

Optionally Drag the Point along the X-axis


If necessary, click Add-Coincident ConstraintRed-14-4 again...

We will now constrain the other Point to be on the Y-axis

STEP 4: Click the Point near to the Y-axisRed-14-5
STEP 5: Click the Y-axis Red-14-6

The Point snaps to the Y-axis.


Again, if you de-select the Add Coincident Constraint icon, you can drag the Point along the Y-axis.

Do you have problems adding the Constraints to the End-Point ?

If you have problems when you want to add a Constraint? The reasons is often:

You fail to select the first or the second element.

Example 1: If you click the first element so that it becomes RED, and then click, but actually fail to click the second element... ...the first element 'de-selects'. You must select the two elements again!

Example 2: If you click, but miss, the first element, and then click the second element and it becomes RED. You must click the first element again.

Example 3: You accidentally click the Point AND the Blue Line as the 'first' element, and then click the axis.

The whole Line becomes collinear with the axis. You must delete the Coincident Constraint and then add it between the Point and the axis again.

How to delete a Constraint

GA-PartEditor-Click Point

Constraints are not visible in the graphic area.

To delete a constraint:

1.Click the sketch-element to which the constraint has been added

The constraint should now be in the Selection-Window.


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

Add Dimensions to locate the Line in the BasePart


Expand the Geometry toolbar to the LEFT of the graphic-area.

STEP 1: Click the Add DimensionRed-14-1b icon


STEP 2: Click the Point that is coincident with the Y-axisRed-14-2
STEP 3: Click the horizontal X-axisRed-14-3

The dimension shows next to your pointer.

STEP 4: Click to put the dimension in the graphic-area


The Edit Dimension dialog-box opens immediately

STEP 5: Edit the dimension

Note: see How to edit a parameter in a dialog-box

Edit the Dimension to be 50.00mm

Note: To edit the Precision and Decimal Places for dimensions in the Application Settings dialog-box | Number-Format > Precision / Digits


Use Add Dimension again to add a dimension to the other Point.

STEP 6: Click the Point on the X-axis, then the Y-axis - or vice versa

The dimension shows next to your pointer.

STEP 7: Click to put the dimension in the graphic-area



See below: 'Why is the dimension negative?'

Enter -120mm In the Dimension dialog-box

But 120mm in the sketch.

The Line becomes CYAN. This shows that the Line is 'fully-constrained'. Now, you cannot drag the Line with your pointer.

Why is the Dimension along the X-axis negative?


Dimensions of a Point relative to a Line or the Part's X or Y-axis.

New convention in MechDesigner Release 10+:

All Lines and Axes have their own Coordinate System - to give an origin and +X-axis and +Y-axis.

That is, Lines have an origin (its start-Point) and a +X-axis direction (from its start-Point to its end-Point), with the +Y-axis direction at +90º to the +X-axis.

This is important when we dimension a Point relative to a Line because the dimension can be negative or positive.

It might be most confusing when we click the Y-axis of a Part as a reference line.


When we click the Y-axis as a reference Line:

the dimension of points to the left are positive - they are along the positive +Y-axis of the Y-axis
the dimension of points to the right are negative - they are along the negative +Y-axis of the Y-axis

When we add the dimension of the Point on the X-axis, and click the Y-axis as a reference Line, the dimension will be negative with respect to the Coordinate System and axes of the Y-axis. Therefore, when we dimension the Point along the X-axis, the dimension dialog-box shows –40.00.

In the image, when we click the Y-axis as a reference Line to a add dimension, then a Point in the area with the patch will be negative

Edit Dimensions (later if needed)


You may need to edit the dimensions with the Dimension dialog-box.

You cannot edit an element in the Part-Editor when a different command is active.

STEP 1: If necessary, click Add Dimension again to de-select Add Dimension.

You must deselect Add Dimension, because you cannot edit a dimension when a command is active.


STEP 2.Hover above the arrowhead of the dimension
or an extension line... (but not the number itself),
...until the dimension becomes selected
STEP 3.Double-click.

OR, click the dimension arrowhead one time, then edit from the Selection-Window.

The Dimension dialog-box opens.


STEP 4: Right-click with your pointer over the dimension of the Dimension dialog-box. The 'Zero / Round' contextual-menu shows next to your pointer. Select 'Round' so the value changes to the nearest integer number that is exactly divisible by the spin-box increment value.
STEP 5: Use the spin-box tool to change the dimension that is between the Point on the X-axis to the Y-axis to 120mm

Do Steps 2-5 again to add the other dimension.

Change the dimension that is between the Point on the Y-axis to the X-axis to 50mm

Close the Part Editor





Part-Editor icon

Close the Part-Editor:

Do one of these procedures:

In the graphic-area:

1.Double-Click the Y-axis at the origin of the Part

- or in the graphic-area:

1.Double-Click the Line that you have added in this tutorials step

- or in the graphic-area:

2.Click the Edit-Part in Editor-Part at the top of the contextual-menu to deselect it.

- or - in the contextual toolbar to the left:

1.Click Edit PartRed-14-1b to de-select it and it toggles out.

Save your Mechanism with CTRL+S



Note: the LineRed-14-1b in the Base-PartRed-14-2 is Green.

In the Part-Editor, the colour of each sketch-element in a Part is Blue or CYAN to indicate if it is under or fully constrained.

In the Mechanism-Editor, the colour of the sketch-elements in a Part agrees with the colour of its Part-Outline.

Therefore, in the Mechanism-Editor, the sketch-elements

Green Part-Outlines have Green sketch-elements


Blue Part-Outline have Blue sketch-elements


The Base-PartRed-14-2 ALWAYS has a rectangular Green Part-Outline, and, thus, when the Mechanism-Editor is active, sketch-elements that are in the Base-Part are ALWAYS Green.

Tutorials and Reference Help Files for MechDesigner and MotionDesigner 14.2 + © Machine, Cam, Mechanism, and Motion Design Software by PSMotion Ltd