### What is a Gear-Pair?

A Gear-Pair is two Gears that rotate in mesh. The ratio of teeth determine their relative rotational speeds of two Parts.

The gears may have fixed centres or moving centres.

The gears may have an external or an internal mesh between the teeth.

### Add Gear-Pair : two different preparations:

There are four elements to select in the Command-Manager, which you must prepare before you can use Add Gear-Pair.

 1 Line 'A' in Part 'A', which must have a Green Part-Outline - to show the Part is a
 2 Line 'B' in Part 'B', which must have a Blue Part-Outline - to show it is a Free-Part and thus, not yet kinematically-defined.
 3 Line 'C' in Part 'C', which must have a Green Part-Outline

Points in Lines 'A' and 'B' are joined with Pin-Joints to the start-Point and end-Point of Line 'C'.

 4 A Dimension that gives the length of the Line in Part 'C'.

Preparation 1: Simple Gear-Pair

Gear-Pair uses three Lines , joined with Pin-Joints, in three separate Parts

 • Line in Part A [with a Green Part-Outline] is joined to Line in Part C [with a Green Part-Outline] with a Pin-Joint..
 • Line in Part B [with a Green Part-Outline] is joined to Line in Part C [with a Green Part-Outline] with a Pin-Joint..

The two Pin-Joints must use Points at the ends of Linesand not any other Points.

 • Line in Part C must have a dimension [not visible in Mechanism-Editor] to define its length.

Preparation 2: Epicyclic Gear-Pair

Gear-Pair uses three Lines , joined with Pin-Joints, in three separate Parts

 • Lines in Part A [with a Green Part-Outline] is joined to Line in Part C [with a Green Part-Outline] with a Pin-Joint..
 • Lines in Part B [with a Green Part-Outline] is joined to Line in Part C [with a Green Part-Outline] with a Pin-Joint..

The two Pin-Joints must use Points at the ends of Linesand , not any other Points.

 • Line in Part C must have a dimension[not visible in Mechanism-Editor] to define its length.

Simple Gear-Pairs:

 How to... Add a Gear-Pair (Simple)

 'Expand' then 'Play' How to... Add a Gear-Pair (Simple)

Epicyclic Gear-Pairs

 'Expand' then 'Play' How to... Add a Gear-Pair (Epicyclic)

Notes:

Other Skills:

Result:

 • MechDesigner draws a Gear-Pair in the graphic-area, with an External Mesh
 • The Free-Part becomes kinematically-defined (Green). It is in the Kinematics-Tree as a Geared-Rocker.
 • The Line-of-Centers becomes a 'Driven-Dimension'. The Number-of-Teeth, Module and Gear Mesh drive the dimension.

You cannot edit the value of the dimension in the Part-Editor. It is a 'Driven Dimension', the dimension is coloured grey.

Do the 'Preparation' above, then:

 STEP 1: Click Add Gear Pair in the Machine elements toolbar

The Command-Manager instruction is:

 Add Gears: DriveR Gear is Green Part; DriveN Gear is Blue Part. Parts joined to Green Line with Pin-Joints.

Select four elements to do Add Gear-Pair. The short hints are:

 1 'Green Line on Gear Part 1'
 2 'Blue Line on Gear Part 2'
 3 'Green Line Joining Gear Centers'
 4 'Centre Distance Dimension'

Select the four elements from 1 to 4.

 STEP 2: Click the 'Green Line on Gear Part 1'

This means: 'Select the CAD-Line in the kinematically-defined Part'. This Part should have a Green

 STEP 3: Click the 'Blue Line on Gear Part 2'

This means: 'Select the 'Rusty Red' CAD-Line in the Part that is not yet kinematically-defined. This Part should have a Blue Part-Outline.

 STEP 4: Click the 'Green Line that joins the Gear Centers'

This Line joins the other two Lines with Pin-Joints. The Line should belong to a Part that has a Green Part-Outline - a Part that is kinematically-defined (Green)

The Part-Editor opens for the Part with the Green Line  to show the Dimension for the length of the Line.

 STEP 3: Click the 'Centre Distance Dimension'

Click an extension line or the arrowhead for the dimension.

Do not click the actual Dimension Value, as this does not work.

Note, you must dimension the actual Line, not the distance between the two Points.

The Command-Manager shows that selected elements as you select them.

You must start with the top element and then each element in turn, until each selection-box has a Green 'tick.

 STEP 3: Click OK in the Command-Manager.

The distance between the Gear-Centres changes, if necessary, to a distance that is a function of the number-of-teeth, module and mesh of the gears.

Gear-Pair elements have External Gear Teeth Form in the default configuration.

All the Parts are kinematically-defined.

The motion of the 'first' Part defines the motion of the 'second' Part.

The 'second' Part is now identified in the Kinematics-Tree as a Geared-Rocker

### How to Edit a Gear-Pair

To edit a Gear-Pair, you must edit the Gear-Pair with the Gear-Pair dialog.

To edit the Gear-Pair element, do:

 1 Click the Gear-Pair in the graphic-area

The Gear-Pair is now in the Selection-Window

 2 Right-click the element
 3 Click 'Edit element' in the contextual-menu.

### How to Add a Profile/Extrusion to a Gear-Pair

 STEP 1: Click 'Home' in the Run menu
 STEP 3: Click one of the gears in the Gear-Pair
 STEP 4: Click OK in the Command-Manager

If the Gear is a complete gear (the default state), the new Polyline sketch-element is a 'closed' sketch-loop.

If you edit the Gear so that it becomes a Gear Segment, then the Polyline will be an 'open' sketch-loop.

To add a Profile, you must edit the Part to 'close' the Polyline. This means you must add sketch-elements that merge with the end-points of the Polyline, so that it becomes a 'closed' sketch-loop.

When you have the 'closed' sketch-loop,