﻿ Getting Started Tutorials - MechDesigner > Tutorial 14: Gear-Pairs / Rack-Pinions > A: Fixed Gear Centres > Compound Gear Trains

# Step 14.3: Compound Gear-Trains

### Compound Gear-Trains

 Schematic of Compound, Three-Stage, Gear Train A Compound Gear Train has a minimum of: •two Gear-Pairs •more than one gear on one or more shafts In MechDesigner, it is easier to add Compound Gear-Trains than Simple Gear-Trains.   The image to the left shows a Compound Gear Train. There are three Gear-Pairs, two shafts have two gears. Therefore, it agrees the definition of the Compound Gear Train.

#### Compound Gear Train – Gear-Pair 1

 We will use the model we have done in the previous Step Add a Gear-Pair with Fixed-centers Edit the number-of-teeth as follows. Here, the number-of-teeth are: Z1=20, Z2=40.   The Gear Ratio is Z1/Z2 = 2 Remember this basic rule:: Three Parts, three Lines, joined together with Pin-Joints. Two Lines must be in Parts that are kinematically-defined.

#### Preparation for Gear-Pair 2

To add a Compound Gear-Train, we use the same basic rule, again, and again.

We need three Parts, each with a Line. There is a Line that is joined to a different Line, each with a Pin-Joint. Two of the Lines that are joined with a Pin-Joint are in Parts that are kinematically-defined. The third Line is in a Part that is not kinematically-defined.

Gear-Pair 2:

Before we start, we have a Line in a kinematically-defined Part.

Line 1 / Part 1 : Line is the CAD-Line in the Driven-Gear of Gear-Pair 1.

We need two more Parts and Lines.

Line 2 / Part 2 : It is a new Line in the Base-Part. It will be the Line that joins the gear-centers

1.Edit the Base-Part

2.Part-Editor: Geometry toolbar > Add Line AND Add Dimension  (the actual length is not important).

IMPORTANT rule: You must MERGE Point and Point

You can Hover + Drag to add Line  from Point OR

3.Part-Editor: Geometry toolbar > Merge-Points : Click Point and then click Point

4.Click the graphic-area to complete the merge-points.

5.Close the Part-Editor

Line 3 and Part 3 : It is a new Part - it will be the Driven-Gear.

1.Mechanism-Editor: Kinematics-toolbar > Add Part: Drag to the Part

2.Mechanism-Editor : Kinematics-toolbar > Add Pin-Joint  Join the start-Point of CAD-Line in Part to the end of Line, with a Pin-Joint.

The length the CAD-Line along Part is not important.

1.Click Machine-elements toolbar > Add Gear-Pair

2.Click the elements, from top to bottom - refer to Preparation images, above

3.Click  at the bottom of the Command-Manager.

You can see the Gear-Pair 2

This is a Compound Gear-Train.

You can do the same actions to add more Gear-Pairs.

This image shows Compound Gear-Train with three Gear-Pairs.

To make the Gears Solid

1.Use the ALT+H to move the model to the home position - this is important.

2.Click Solids Toolbar > Add Polyline

3.Click a Gear in one of the Gear-Pairs

4.Do 2 and 3 for each Gear-Pair

5.Click Solids toolbar > Add Profile

6.Click each Gear with a Polyline

7.Do 5 and 6 for each Gear

8.Shift+Click each Profile to see the Profile and Extrusion in the Selection-Window.

9.Edit each Extrusion, to offset it etc, to give a model similar to the image to the left.

10.Edit the Parts to add shafts etc.