What is a Slide-Joint?

MechDesigner definition: a Slide-Joint makes a Line in a Part become co-axial (coincident) with a Line in a different Part. The two Parts can slide along relative to each other.

IFTOMM Kinematic definition: a Slide-Joint makes an axis in one part become collinear with an axis in a different part, but allows the axes to slide relative to each other.

hmtoggle_plus1Theme and Styling of images below:

Edit menu > Application-Settings > General tab > Theme Options > Active Theme: Charcoal Dark Slate,

Edit menu > Application-Settings > Graphics tab > Display Colours :  (Background : White) ;  (Part-Unsolved : Blue) ; (Part-Solved: Green) ;( Joint-Solved : Green) ; (Joint-Unsolved : Blue)

Add Slide-Joint

Add Slide-Joint icon

Kinematic Elements Toolbar : Add Slide-Joint icon (<<left of graphics-area)

Menu :

Add menu > Mechanism sub-menu > Add Slide-Joint

Dialog-Box :


IMPORTANT: To correctly calculate reaction forces for a Slide-Joint:

There is often more than one Slide-Rail and Slide-Bearing that run in parallel in your actual design.

However, a Slide-Joint is constructed from a Line in two Parts, that are made collinear.

The length and position of the Lines that define a Slide-Joint must be equivalent to the actual design.


Slide-Joint in the graphic-area:

Red-14-1b Narrow Rectangular Box - its length is equal to the length of Line '1' you select for the Slide-Joint

Red-14-2 Wide Rectangular Box - its length is equal to the length of Line '2' you select for the Slide-Joint

Red-14-3 Arrowhead to show Positive-Direction* - is at the start-Point of one of the two Lines you select for the Slide-Joint

* Positive-direction becomes important when you add a Motion-Dimension FB to the Slide-Joint.

See Positive direction of Slide-Joints and Motion-Dimension

See also: Add Pin-Joint, Add Ball-Joint, Add Motion-Dimension FB


Before you can do add Slide-Joint you must have a minimum of two Parts, and a Line* in each Part. A minimum of one Part must be a free Part, which has a Blue Part-Outline.


1.A Line*Red-14-1b that is a child to a free Part
2.A Line*Red-14-2 that is a child to:
a different free-Part

- or -

In this image: lineRed-14-2 is in the Base-Part (Rectangular Green Part-Outline is not shown), which is always a kinematically-defined Part, and LineRed-14-1b is the CAD-LineRed-14-1b along the centre of an Added-Part.

* Line or CAD-Line

Add Slide-Joint:



STEP 1: Click Add Slide-Joint


Add menu > Mechanism sub-menu > Add Slide-Joint

Kinematic Elements Toolbar : Add Slide-Joint icon

STEP 2: Click the two Lines:

1.Click a LineRed-14-1b in a Free-Part
2.Click a LineRed-14-2 in a different Part

If the Select-Elements dialog-box opens, you have clicked more than two Lines.

1.CTRL+Click the two Lines (in two different Parts) in the Select-Elements dialog box.
2.Click OK-tiny-13-17 to close the Select-Elements dialog-box

See also Slide-Joint Special Case.

STEP 3: Complete the command

If the two Lines do not snap together:

1.Click the graphic-area

The two Lines become collinear.



A new Slide-Joint


In this image, the new Slide-Joint belongs to an Unsolved Mechanism .

A Part in the Slide-Joint is not kinematically-defined, and has a Blue Part-Outline.

VIDEO: Add Slide-Joint - Simple-Case


How to

add a Slide-Joint





A new Slide-Joint


In this case, the new Slide-Joint in an Unsolved-Mechs as the Part-Outline is Blue in the model above

tog_minusSpecial Case: Two or more collinear Slide-Joints

Frequently, a machine design has two or more Slide-Joints between three or more Parts

We must decide which two Lines from which of two Parts we want to select for each Slide-Joint.

For example:

There are a total three Parts and we would like to join all three Parts to one sliding axis. We must add two Slide-Joints:

If, say, Slide-Joint#1 is between Lines 1 & 2 (in Parts 1 & 2), there are two options for Slide-Joint#2:

Option A: Slide-Joint#2 between Lines 3 & 1 (in Parts 3 & 1)

Option B: Slide-Joint#2 between Lines 3 & 2 (in Parts 3 & 2)

When to do Option A or Option B becomes important when you need to also add Motion-Dimension FBs to specify the motions of the two Parts.


Preparation for this example:

A. Slide-Joint: a joint of two collinear Lines :
LineRed-14-1b is in a kinematically-defined Part (obviously) as it is coloured Green
CAD-Line along the centre of PartRed-14-2, which is collinear with LineRed-14-1b
B.Completely-Free PartRed-14-3, which includes a CAD-Line along its centre.


A minimum of one Part must be a free Part.  However, one Part, two Parts, or all three Parts may be free Parts.


STEP 1: Click Kinematic-elements Toolbar > Add Slide-Joint


STEP 2: Click the CAD-LineRed-14-4 along the center of the Completely-Free Part


The Slide-Joint does not need to be with the CAD-LineRed-14-4.

Generally, a Slide-Joint can be with any Line in a Part.


STEP 3: Click the two LinesRed-14-5 in the Slide-Joint


Now we have clicked a total of three Lines.

The Slide-Joint is between two Lines only.

Thus, there is ambiguity as to which two Lines you want for the Slide-Joint.

'Ambiguity': when MechDesigner is not sure which element to select.


Select-Elements dialog-box

When there is ambiguity as to which two Lines you want to select, the Select Elements dialog-box opens.


If you can anticipate that there might be ambiguity as to which elements you need to select, we recommend:

If possible, click first an element that does not have ambiguity
Then, click an element that might have ambiguity.

In the Select-Elements dialog-box, the element at the top of the list is always the first element you select.



When we follow our recommendation, the Line at the top of the list is CAD-LineRed-14-4 - it has the element-name of CAD-Line2

We definitely want to select CAD-Line2 for the new Slide-Joint.

The ambiguity is which Line from the other two LinesRed-14-5 we want to select for the new Slide-Joint.

To select the Lines

1.Ctrlb key down - do this before you click the Lines in the box.
2.Select all of the Lines we want to use for the new Slide-Joint

Generally, mathematically, you can combine two elements from three elements in three possible ways. 1&2; 2&3; 3&1

However, MechDesigner will select only those elements that you can combine to add the new element.

Thus, you can select:

CAD-Line2 and Line3 (image above)

- or -

CAD-Line2 and CAD-Line (image left)




However, you cannot select:

CAD-Line2 and CAD-Line (image left)

Why? MechDesigner knows there is a Slide-Joint between these two CAD-Lines already.


In the Select-Elements dialog-box.

STEP 3: Click the two Lines
1.Ctrlb key down
2.Click to select all Lines in the Select-Elements dialog-box to do Add Slide-Joint
STEP 5: Click OK-tiny-11-15 in the Select-Elements dialog-box.

The Select-Elements dialog-box closes.

The two Lines become collinear.

If they do not become collinear...

STEP 6: Click the graphic-area

The two Lines become collinear to add a new Slide-Joint,

Now, there are two Slide-Joints and three Lines that are collinear.

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