﻿ Compound Gear Trains

# Step 14.3: Compound Gear-Trains

### Compound Gear-Trains

Schematic of Compound, Three-Stage, Gear Train

A 'Compound Gear Train' has at least:

 • two Gear-Pairs
 • one shaft with more than one gear

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 is more than one gear-pair and two shafts have two gears.

Therefore, it agrees the definition of the Compound Gear Train.

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

 Start with a Gear-Pair with an External Mesh- see Option 1 Step 14.1 Here, the number-of-teeth are: T1=20, T2=40. The Gear Ratio is T1/T2 = 2 Use the rule: 'Three Parts, with three Lines, joined together with two Pin-Joints' Note 1: In this Tutorial, we sketch the Lines-of-Centre between the gears in the Base-Part.

#### Prepare Compound Gear-Train – Stage 2

Again, we need three Lines, in separate Parts, with Pin-Joints that join the three Lines end-to-end.

Line 1 and Part 1 – see image.

The Input Shaft to the second Gear is the Output Shaft of the first Gear-Pair. It also has a Line along it.

Hence, we do not need to add anything for Line1/Part1/Joint1.

Line 2 and Part 2

'Line-of-centres'.

Because this Gear-Pair also has 'fixed-centres' , this Line must also be in the Base-Part.

 1 Edit the Base-Part – Double-click it.

 Note the Length of the Line-of-Centres for the first Gear-Pair = 120mm. Why? Module = 4; Teeth are 20 and 40; Centre Distance = 4*((20+40)/2) = 120mm.
 3 Add a dimension to the Line
 4 Use Merge-Points to merge the Point (the Point at the end of the Line-of-Centres for the first Gear Pair), and Point at the end of the new Line
 5 Close the Part-Editor

 6 Add a Part , with a Pin0Joint at the end of the new Line. The length of the Part is not important.

#### Add Compound Gear Train – Stage 2

(Element 4 is the Dimension of Line 3)

Preparation of Model to add the Third Gear-Pair.

 2 Click the four elements

You can see the new Gear-Pair.

The module is different. Usually, Gears have the same module throughout a Compound Gear Train.

Use the Gear-Pair dialog-box to edit

 1 The Module to 4
 2 The number-of-teeth on Gear 1 to be 30
 3 The number-of-teeth on Gear  2 to be 50

The image shows the Two Gear-Pairs

 • Gear-Pair in Blue
 • Gear-Pair in Red

#### Prepare and Add Compound Gear Train – Stage 3

Preparation – the same as Stage 2.

 1 The New Line in the Base-Part ...
 2 ... with the end Point in the Line merged to the Point at the centre Gear 2 in the Second Stage
 3 A New Part Joined to the end of the new Line.

As before, we will use the Part that has Gear 2 of Stage 2, as the Part for Gear 1 of the Stage 3.

You can see the Gear-Pair Stage 3 – in red.

The module is different. Usually, Gears have the same module throughout a Compound Gear Train.

Use the Gear-Pair dialog-box to edit:

 1 The Module to 4
 2 The number-of-teeth on Gear 1 to be 22
 3 The number-of-teeth on Gear  2 to be 52

The image shows the complete Compound Gear Train.

Frequently, the centre of the Gears in Compound Gears are in line:

 1 Edit the Base-Part – double-click it
 2 Use Add Horizontal to the Lines for each 'Line-of-centre'.

Important: Merge the Points at the ends of each Line.

Here is the third stage of the Compound Gear Train.

To make the Gears 'Solid':

 1 Use the Home key to make sure the model is at the home position - this is important.
 2 Click Solids Toolbar : Add Polyline
 3 Click a Gear in one of the Gear-Pairs To see the Polyline as a copy of the Gears, click the Gear-Pair to see the Gear-Pair and Polyline elements in the Selection-Window.
 4 Repeat 2 and 3 for each Gear-Pair