Step 14.3: Compound Gear-Trains

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Step 14.3: Compound Gear-Trains

Compound Gear-Trains

Schematic of Compound, three stage, Gear Train.

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.

See Also: Simple Gear-Pair, Simple Gear-Trains, Planetary Gear-Trains


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=20Red-14-2, Z2=40Red-14-3.  

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.

Gear-Part 2: Prepare and Add

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 : LineRed-14-5 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 LineRed-14-1b AND Add DimensionRed-14-2  (the actual length is not important).

IMPORTANT rule: You must MERGE PointRed-14-3 and PointRed-14-4

You can Hover + Drag to add LineRed-14-1b  from PointRed-14-3 OR

3.Part-Editor: Geometry toolbar > Merge-Points : Click PointRed-14-3 and then click PointRed-14-4

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 PartRed-14-6

2.Mechanism-Editor : Kinematics-toolbar > Add Pin-Joint  Join the start-Point of CAD-Line in PartRed-14-6 to the end of LineRed-14-1b, with a Pin-Joint.

The length the CAD-LineRed-14-7 along PartRed-14-6 is not important.


We are ready to Add Gear-Pair

Add Gear-Pair 2


Add Gear-Pair 2

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

2.Click the elements, Red-14-5Red-14-7Red-14-1bRed-14-2 from top to bottom - refer to Preparation images, above

3.Click OK-tiny-11-15  at the bottom of the Command-Manager.


You can see the Gear-Pair 2Red-14-2


MechDesigner adds two new gears.

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.