Step 1.3: Edit the Base-Part, Add a Line

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Step 1.3: Edit the Base-Part, Add a Line


We want to join the new Part to the Base-Part with a Pin-Joint. To do this, we need only a Point in the Base-Part and a Point in the Part. However, we will add a Line. We will see why we add a Line in Step 1.4

Objective of this Step:

Learn how to open and close the Part-Editor.

Learn how to add and delete sketch-elements, dimensions and constraints.

Learn that some dimensions are negative - it is a MechDesigner Rule!

Learn that sketch-elements change their color when they are fully defined.

Summary of this Tutorial:

1.Open the Part-Editor to edit the Base-Part.

2.Add a Line sketch-element

3.Add Dimensions and Constraints to locate the Line in the Base-Part.

4.Optionally, delete a Constraint

5.Close the Part-Editor to return to the Mechanism-Editor.


Tutorial 1: STEP 1.3 Add Line to the Base-Part


Edit the BasePart with the Part-Editor


The green rectangle is the symbol and Part-Outline of the Base-Part

We will use the Double-click method to open the Base-Part:

STEP 1: Double-Click the Green rectangular Part-Outline

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 geometry to a Part.

Geometry includes: sketch-elements, constraints, and dimensions that you add to and between sketch-elements.


When the Part-Editor is active:

We do not show the Part-Outline

The small axes change to the large axesRed-14-1b

The Mechanism name-tab changes to Part name-tabRed-14-2 - Not from MD16.1 +

To the left of the graphic-area, the Geometry toolbarRed-14-3 becomes available when you click the Collapse/Expand icon

To the right of the graphic-area, the Constraints toolbar becomes available when you click the Collapse/Expand icon

The Edit Mechanism pointer changes to the Edit Part pointerRed-14-4

The Edit Part in Part-Editor icon is toggled inRed-14-5

Add a Line to the Base-Part

+ Line 

+ Line

Now, add a Line to the Base-Part:

STEP 1: Expand the Geometry toolbar

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


Your pointer changes to the Add Line pointer.

STEP 3: Drag in the graphic-area to add a Line

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

Mouse-button down...move your mouse-pointer...mouse-button up

A Line shows in the Part-Editor.

We must position 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

Note: 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:

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:

You accidentally click the 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 Base-Part


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-Value

Edit the Dimension to 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 changes its color. 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/ Copy/Paste 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

Do one of the following to close the Part-Editor:





Part-Editor icon

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

Close the Part-Editor

Close the Part-Editor

The Line in the Mechanism-Editor

The Line in the Mechanism-Editor

Note: the LineRed-14-1b and the Base-PartRed-14-2 are Green.

In the Part-Editor, the color 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 color of the sketch-elements in a Part agrees with the color 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.