# AutoCAD 3D exercise: a pulley

> Model a pulley in AutoCAD 3D: its half section as a closed polyline, revolved round the Y axis into a solid, solved step by step. Practise 3D free online.

Model this pulley by revolving its half section round its axis, in millimetres: a bore of 20, a hub 30 long and 40 across, a web 10 thick and a rim 24 wide from 90 to 110 across, centred on the hub. The section is drawn as distances from the axis, which runs up the Y axis, so each diameter is drawn as its half.

- **Exercise:** Intermediate · Mechanical · 3D solid
- **Commands:** [`PLINE`](https://mellowcad.com/docs/commands/pline.md), [`-VIEW`](https://mellowcad.com/docs/commands.md#-view), [`VSCURRENT`](https://mellowcad.com/docs/commands/vscurrent.md), [`REVOLVE`](https://mellowcad.com/docs/commands/revolve.md), [`ZOOM`](https://mellowcad.com/docs/commands/zoom.md)
- **In the editor:** [Open it with its drawing](/draw?drawing=pulley), dimensioned beside where you draw yours

## The drawing

The pulley's half section beside its axis, its distances from the axis dimensioned.

The pulley as a solid, seen from the south-east in the Conceptual visual style.

## Step by step

The engine draws each step and writes its history as you would type it: the prompts in AutoCAD 2027's order, with the same option letters. After a command's first point, a typed point is measured from the last one, as dynamic input measures it, and the history writes it with @; \# measures from the origin.

### 1. Draw the half section

On the Outline layer, one closed [`PLINE`](https://mellowcad.com/docs/commands/pline.md) from `10,0`, each point after it a step from the last: `10,0`, `0,10`, `25,0`, `0,-7`, `10,0`, `0,24`, `-10,0`, `0,-7`, `-25,0`, `0,10` and `-10,0`, then `Close`.

1. Draw the half section

```text
Command: PLINE
Specify start point: 10,0
Current line-width is 0.00
Specify next point or [Arc/Halfwidth/Length/Undo/Width]: @10,0
Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]: @0,10
Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]: @25,0
Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]: @0,-7
Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]: @10,0
Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]: @0,24
Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]: @-10,0
Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]: @0,-7
Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]: @-25,0
Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]: @0,10
Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]: @-10,0
Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]: C
```

### 2. Turn the view

`-VIEW` and `SEIso` look at it from the south-east and above; [`VSCURRENT`](https://mellowcad.com/docs/commands/vscurrent.md) and `Conceptual` shade the faces, which shows a turned part best.

2. Turn the view

```text
Command: -VIEW
Enter an option [Orthographic]: SEI
Regenerating model.
Command: VSCURRENT
Enter an option [2dwireframe/Hidden/Conceptual] <2dwireframe>: C
```

### 3. Revolve it

[`REVOLVE`](https://mellowcad.com/docs/commands/revolve.md): pick the section and press Enter, then `Y`: the Y axis is the pulley's. Enter takes the default angle, a whole turn. [`ZOOM`](https://mellowcad.com/docs/commands/zoom.md) `Extents` frames it, and a scale of 0.8x leaves room round it.

3. Revolve it

```text
Command: REVOLVE
Current wire frame density:  ISOLINES=4, Closed profiles creation mode = Solid
Select objects to revolve or [MOde]: 1 found
Select objects to revolve or [MOde]:
Specify axis start point or define axis by [Object/X/Y/Z] <Object>: Y
Specify angle of revolution or [STart angle/Reverse/EXpression] <360>:
Command: ZOOM
Specify corner of window, enter a scale factor (nX or nXP), or [All/Extents/Previous/Scale/Window/Object]: E
Command: ZOOM
Specify corner of window, enter a scale factor (nX or nXP), or [All/Extents/Previous/Scale/Window/Object]: 0.8x
```

## More exercises

- [AutoCAD exercise: a link with tangent lines](https://mellowcad.com/docs/exercises/link.md): Advanced · Mechanical · 2D
- [AutoCAD 3D exercise: a bearing block](https://mellowcad.com/docs/exercises/bearing-block.md): Advanced · Mechanical · 3D solid
- [AutoCAD exercise: a gasket](https://mellowcad.com/docs/exercises/gasket.md): Beginner · Mechanical · 2D
- [AutoCAD practice exercises](https://mellowcad.com/docs/exercises.md)