Rack-Pinion and Ball-Screw dialog-box

See Add Rack-Pinion

Use the Rack-Pinion and Ball-Screw dialog-box to edit parameters for a:

Rack and Pinion and

How to open the Rack-Pinion dialog-box

To open the Rack-Pinion / Ball-screw dialog-box, there must be a Rack-Pinion or Ball-screw in the model - see Add Rack-Pinion

1.Double-click a Rack-Pinion element (the actual Gear-Teeth) in the graphic-area.

- or -

1.Click the Rack or the Pinion in the graphic-area or Assembly-Tree.

The Rack-Pinion element shows in the Selection-Window.

2.Right-click the Rack-Pinion element in the Selection-Window.
3.Click 'Edit Element...' in the contextual-menu.

Rack-Pinion / Ball-Screw dialog-box

Rack & Pinion dialog-box [With Ball-Screws tab]

Rack & Pinion dialog-box
[With Ball-Screws tab]

There are three tabs in the Rack-Pinion dialog-box.

General  tab : Rack and Pinion Parameters

Gear Tooth tab : Rack and Pinion Tooth Parameters

Ball-screw tab : Ball-Screw Parameters

General tab : Rack and Pinion Parameters 


Rack Offset

Rack Offset : moves the rack along its pitch-line by a number of teeth.

'# Rack Teeth, N

Rack Tooth, N : the number-of-teeth along the Rack

# Pinion Teeth, N

Pinion Tooth parameter box gives the Pinion's number-of-teeth.

As you increase the number-of-teeth on the Pinion, the Rack will move to remain in contact with the Pinion.

To correct the Mesh:

When you want to add two Racks to the same pinion, you must do Add Rack-Pinion two times.

You may need to rotate one of the Pinions a fraction of a gear tooth so that the two pinions are appears to be the same. To do this, click one of the options:

Shift Rack, or
Shift Pinion, or
Do not Shift

Select Rack Side

The Rack is one side of the pinion or the other. Select:


- or -


Gear Tooth tab : Rack and Pinion Tooth Parameters


Module = P.C.D (mm) ÷  number-of-teeth.

Ratio [degrees / mm] [Read-Only]

The 'degrees of rotation' of the Pinion for each 'mm' travel of the Rack.

P.C.D (Pitch Circle Diameter) [mm] [Read-Only]

The diameter of the Pitch Circle of the Pinion

Pressure Angle [Default = 20º].

The 'standard' Pressure Angle is 20º. Other 'standards' are: 14º, 17.5º (weaker, quieter), 22.5º and 25º (stronger, noisier)

Addendum [Default = Module].

The radial height of the gear tooth from the pitch circle to the tip of the tooth.

Dedendum [Default Value = Module * 1.25 (Module>1)].

The radial depth of the gear tooth below the Pitch Circle to the root of the tooth. It is larger than the Addendum so there is clearance. Then the tip of the tooth is clear of the root of the

Root Radius, or 'Flank Radius' [Default is 0.3 * Module]

The small fillet between the Flank and the Root of the Gear Tooth.

Points along Profile

The number of 'facets' along the gear tooth flank. ':  ' is 'OK', 8 is 'Good'.

Ball-Screw tab : Ball Screws Parameters 


Note: Typically, if you plan to change the Rack-Pinion to become a Ball-Screw, then it is most usual that the 'Part whose motion is defined with a Motion-Dimension FB [kinematically-defined Part] is the Sliding-Part, and the 'Driven Part' is the Pinion. That is to say, the motion is defined for the 'Nut'.

Select Type

Rack and Pinion

Click the Ball-Screw 'radio-button' to change the element to a Ball-Screw.

Ball-Screws - the symbol in the graphic-area changes to a 'screw', starting at the origin of the Sliding-Part.

Ball-Screw Lead - [Screw-Pitch] [mm] - the distance the Sliding-Part must move to rotate the Rotating-Part one time.
Ball-Screw Diameter [mm] - to edit the diameter of the rectangular and screw thread symbol.


The Ball-Screw has a 'Right-Hand Thread' when the Rack-Side is set to Right - see General tab : Rack and Pinion Parameters

The Ball-Screw has a 'Left-Hand Thread' when the Rack-Side is set to Left - see General tab : Rack and Pinion Parameters 

The Module, in the Gear Parameters tab, changes to a value that is equivalent to the Ball-Screw Lead


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