In the next step, Step 1.4, we will make a Pin-Joint between a Point in the 'Added-Part' [Step 1.2]and a Point in the Base-Part.

The Base-Part does not have a CAD-Line, or any other geometry. Thus, we must add geometry to it.

Before we can make a Pin-Joint between the Base-Part and the Added-Part, we must add a Point to the Base-Part.

However, we will add a Line to the Base-Part.

Note: Each Added-Part has a CAD-Line along its centre. Lines and CAD-Lines have a Point at its a start-Point and a Point at its end-Point.

Objective of this Step:

Learn how to start and close the Part-Editor.
Learn how to add and delete sketch-elements, dimensions and constraints in the Part-Editor.
Learn why 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 position 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:

Start the Part Editor to Edit the BasePart


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 axes1s-red
The Mechanism name-tab changes to Part name-tab2s
The Kinematic-elements toolbar is not available, the Geometry toolbar3s becomes available.
The Mechanism pointer changes to the Edit-Part pointer4s
The Part-Editor icon is toggled in5s

Add a Line to the Base-Part


Now, add a Line to the Base-Part:

STEP 2: Expand the Geometry toolbar at the LEFT-SIDE of the graphic-area
STEP 3: Click Geometry toolbar > Add Line 1s-red


Your pointer changes to the Add Line pointer.

STEP 3: Drag a Line

The Drag technique to 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.


The Line, the end-Point and the start-Point are Blue. You can drag the Line and the Points with your mouse-pointer (Mouse-button down on the Line or one of the Points, and move your pointer).

Add Coincident Constraints to the Line


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

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

Notice your cursor changing to the 'Add Coincident Constraint'.

Click two elements to add a Coincident Constraint.

In this case we will do Add Coincident Constraint two times: we will select the X-axis and a Point and then the Y-axis and a Point.



You cancel the first element if you miss the second element! Start again!

STEP 2: Click the Point2s that is near to the X-axis
STEP 3: Click the X-axis3s

The Point 'snaps' to the X-axis.

Optional: If you de-select the Add Coincident-Constraint , you can still drag the Point along the X-axis:

1.Move your mouse-pointer above the Point on the X-axis so that it becomes RED
3.Move your mouse left-to-right



If necessary, click Add-Coincident Constraint4-R-RED-15 again...

STEP 4: Click the Point near to the Y-axis5s-b
STEP 5: Click the Y-axis 6-R-RED-15

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.

Having Problems adding the Constraints to the Line?

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

'You are not precise enough when you select the first or the second element'.


Example 1: If you click the first element so it becomes RED, and then click, but miss, 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 Line as the 'first' element, and then click the axis.

The whole Line becomes co-Linear with the axis. You must delete the Coincident Constraint and then add the constraint 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-SIDE of the graphic-area.

STEP 1: Click Add Dimension1s-red in the toolbar


STEP 2: Click the Point that is coincident with the Y-axis2s
STEP 3: Click the horizontal X-axis3s

The dimension shows next to your pointer.

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


The Edit Dimension dialog-box opens.

STEP 5: Edit the dimension in the Dimension dialog-box

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

Edit the Dimension to be 50.00mm

Note: You can edit the number of Decimal Places for dimensions in the Application Settings dialog-box | Number-Format.


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

STEP 6: Click the Point on the X-axis4s, then the Y-axis5s - or vice versa

The dimension shows next to your pointer.

STEP 7: Click-pause-click to put the dimension in the graphic-area and open the Dimension dialog-box



See below: 'Why is the dimension negative?'

Edit the dimension in the Dimension dialog-box to 120mm

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 (Origin and +X,+Y) .

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 dimension a Point, then Points in the area with the 'patch' will be negative in the Coordinate System of the Y-axis.

Edit Dimensions [later if needed]


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

STEP 1: If necessary, click Add Dimension1s-red again to deselect the Add Dimension command.

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


STEP 2: Hover above the dimension arrowhead2s ...
or an extension line... [but not the number itself],
...until the dimension becomes red
STEP 3: Double-click.

OR, Click one time, then edit from the Selection-Window.

The Dimension dialog-box opens.


STEP 4: Right-click with your pointer in the dimension box in 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 for 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

To 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 icon in the command-palette.

- or -

To the LEFT-SIDE of the graphic-area:

De-select the Edit Part icon 1s

1.Click Edit Part icon so it toggles out, again.



Note: the Line1s-red in the Base-Part2s 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, each Part has a::

Green Part-Outline with Green sketch-elements

or a

Blue Part-Outline with Blue sketch-elements


The Base-Part2s 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.

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