Mechanism | Add Magnetic-Joint

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Mechanism | Add Magnetic-Joint

Add Magnetic-Joint

See also: Magnetic-Joint dialog

What is a Magnetic-Joint?

A Magnetic-Joint pulls a circular Profile, that is in one Part, to be in continuous contact with an irregular Profile, that is in a different Part.

The shape of the irregular Profile is calculated from a Point-Cloud, or it is the shape of a Profile.

Why use a Magnetic-Joint?

A frequent application of the Magnetic-Joint is to reverse-engineer a cam, and to find the motion of a cam-follower from the shape of the cam.

Prepare the Magnetic-Joint

See also RULES

There are two kinematic-chains - one with an Irregular Profile, and the other with a circular profile



Irregular-ProfileRed-14-2 : a Curve calculated from a Point-Cloud, or a Profile.

Irregular-ProfileRed-14-2 : is a child to any PartRed-14-1 that is in a kinematically-defined chain, or it may be child to the Base-Part.

In this model, the irregular-shapeRed-14-2 is a child to PartRed-14-1b, which is a Rocker/Crank.


Circular-ProfileRed-14-4 : a Profile.

Motion-Dimension FBRed-14-3 specifies the position of a kinematically-defined chain, in which the Circular-ProfileRed-14-4 is a child to PartRed-14-5

In this model, Motion-Dimension FBRed-14-3 specifies the position of PartRed-14-5 in which the Circular-ProfileRed-14-2 is a child.


PartRed-14-1 and PartRed-14-5 will usually move relative to each other.

PartRed-14-1 and PartRed-14-5 will usually be in different kinematic-chains.

PartRed-14-1 and PartRed-14-5 might be in one kinematic-chain, but with at least two Motion-Dimension FBs.

After you do Add Magnetic-Joint, Motion-Dimension FBRed-14-3, becomes driven by the Magnetic-Joint


Shape of the Irregular-Profile

1.Preferably, you apply a Tangent Constraint between the sketch-elements that define the shape of the Irregular-Profile.

2.|Radiusmin| of Irregular-Profile > Radius of Circular-Profile (taking the Circular-Profile to have a positive radius).

Immediately before you do Add Magnetic-Joint

1.Home the model with the ALT+H key combination.

With respect to which surface of the Irregular-Profile you want the Circular-Profile to be in contact : its Outside-Surface or its Inside-Surface:

2.Edit Motion-Dimension FBRed-14-3 | Base-Value to move the Circular-Profile so that the:

a)- Normal distance from Circular-Profile to the Irregular-Profile < 0.5 × Radius of the Circular-Profile

or, equivalently, the:

b)- Normal distance from the center of the Circular-Profile to the Irregular-Profile  < 1.0 × radius of the Circular-Profile

Add Magnetic-Joint

Toolbar :

Machine Elements Toolbar

Add Magnetic-Joint icon

Machine Elements Toolbar : Add Magnetic-Joint icon

Menu :

Add menu > Mechanism sub-menu > Add Magnetic-Joint

Dialog :

Magnetic-Joint dialog-box



Red-14-1b The Part on which the Irregular-ProfileRed-14-2 is a child.

Red-14-2 The Irregular-Profile - a Profile or a Curve calculated from a Point-Cloud

Red-14-3 The Motion-Dimension FB that will become driven by the Magnetic-Joint and the contact between the Circular-ProfileRed-14-4 and Irregular-ProfileRed-14-2.

Red-14-4 The Circular Profile

Red-14-5 The Part to which the Circular-Profile is a child.



1.Click Run menu > Home  ( or the ALT+H key combination).

2.Edit the Motion-Dimension FBRed-14-3 | Base-Value to move the Circular-ProfileRed-14-4 to be near to Irregular-ProfileRed-14-2

3.Click Machine elements toolbar > Add Magnetic-Joint

4.Click the Irregular ProfileRed-14-2

5.Click the Motion-Dimension FBRed-14-3

6.Click ProfileRed-14-4

7.Click OK-tiny-13-17 in the Command-Manager




The Magnetic-Joint pulls the Circular-ProfileRed-14-2 to be in contact with the Irregular-ProfileRed-14-4.

A Point SymbolRed-14-6 is at the contact.

The Magnetic-Joint FBRed-14-7 shows near to the Point-SymbolRed-14-6

A Magnetic-Joint iconRed-14-8 is near to the Motion-Dimension FBRed-14-3 that becomes driven by the Magnetic-Joint.


The Magnetic-Joint does not use closed-form mathematical equations. The position of the Magnetic Driven-Part is solved with iterative, root-finding techniques.

The Magnetic-Joint may fail if the Circular-Profile and Irregular-Profile cannot stay in continuous contact for a complete machine-cycle.

Wait, if you have many Magnetic-Joints in one model.

See also: Magnetic-Joint dialog-box, Add Profile, Sketch-Loop, Add Motion-Dimension FB; YouTube Video :



How to...

Add Magnetic-Joint