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Gear tutorial : Making a gear

This tutorial will show you how to make a gear like this one in AC3D. Version 6 was used for this tutorial.

You can download the gear in this example here.

Step 1 : Preparation

Turn on the AC3D grid (using the "Gridsnap" checkbox in the lower left of the AC3D window). Set the grid to whatever you'd like. I used a Major grid of 1.0 and a Minor grid of 0.1. You can set the grid size using the File -> Settings menu.


Step 2 : Making a tooth

Click the "Line" button on the left hand control panel. This will activate line drawing mode. Draw a line along the Y axis as shown. I started the line at 1.0 units from the origin, and extended it for 0.2 units. Draw the line by clicking on the grid in the appropriate places. End the line by right clicking.

As mentioned, make sure Gridsnap is checked.

With the line selected, perform an Object -> Revolve with the following settings (this gear will have 64 teeth when we're done).
degrees: 360
axis: Z
segments: 64
offset: 0

In Surface mode, select all geometry (Ctrl+A) and Shift+Right-click the top surface shown.

Delete these surfaces.

Select the remaining surface and divide it twice (Surface -> Divide).

Select the top-right four surfaces.

Delete these surfaces.

Select the top 4 surfaces.

Perform a Surface -> Combine. Do the same for the bottom-left 4 surfaces and the bottom-right 4 surfaces.

In Vertex select mode, select all vertices that ended up "in between" our new surface sides.

Delete these.


Step 3 : Making a quadrant of the gear

Go back into Object mode and select the tooth template. Perform a Tools -> Replicator, and set the following options.

Copies: 15
Mode: Duplicate
Translation: 0, 0, 0
Rotation: 0, 0, -5.625
Rotate about: Origin
Scale: 1, 1, 1


Why -5.625

We know if we created 63 copies of this tooth and arranged them around the origin, we will have a complete gear tooth outline, because our tooth was created from a 64-segment revolution.

So when we replicate our tooth, we want to rotate it 360 degrees divided by the number of segments, or:

360 / 64 = 5.625

We created 15 copies because we are only interested in getting the top-right 16 teeth for now.

Close the replicator window, select all of our teeth, and perform an Object -> Merge to get the teeth into a single object.

Go into Vertex mode and perform a Vertex -> Snap together by distance, with a distance of 0.005. This will ensure that vertices that "seem" to be in the same place are *exactly* in the same place.

Next, in Object mode, perform an Object -> Optimize vertices. You should see a message that 30 vertices were removed.

Select the "inner" vertices of the gear outline as shown.

Perform a Vertex -> Extrude edges (Ctrl+E). Nothing will appear to happen, but new vertices/surfaces were just created. Drag the selected vertices along the positive Z axis in the Left view as shown.

Perform another Extrude edge and, in the Front view, resize using the upper-right selection handle to shrink the selection toward the origin.

Keep performing edge extrusions until you have the following shape.


Step 4 : Creating spokes (optional)

For a plain round gear, you can skip this step, but if you want spokes, select two or more surfaces in the center (shown below).

Perform an Edit -> Select loop (L).

Unselect 5 of the surfaces on the left and bottom edges.

Delete the selected surfaces.

In Vertex mode, select two or more adjacent vertices around the new hole we made in the 3D view.

Perform another Select loop to select all vertices around the hole.

Perform an Edge extrude and push the vertices back along the negative Z axis.


Step 5: Adding depth to the teeth and gear

Select the top two vertices of any gear tooth and perform a Select loop (L). Important: DO NOT select the vertices shown in red.



Perform an Edge extrude and push the vertices back along the negative Z axis. If you followed step 4, these vertices will now be on the same Z plane as the backs of the hole we created.

We have a some extra surfaces on the inside, under each tooth. Select them (you wil have to select each individual surface) and delete them.

Step 6 : Finishing the gear

In Object mode, select the gear quadrant and perform a Tools -> Replicator.

Copies: 3
Mode: Duplicate
Translation: 0, 0, 0
Rotation: 0, 0, 90
Rotate about: Origin
Scale: 1, 1, 1

Select all 4 pieces and perform the following steps, similar to before:

Object -> Merge
Go into Vertex mode
Vertex -> Snap together by distance (0.005)
Go into Object mode
Object -> Optimize vertices

Now perform an Object -> Mirror -> -Z

This is a rather clunky looking gear, but a subdivision will get it looking smooth. Here is the gear with two levels of subdivision applied.

You can resize the gear to make it skinnier, etc.


Appendix : If this gear is too big

This is a fairly robust gear polygon-count-wise. You can reduce the size of the gear in several ways.

Reducing the number of teeth will naturally make the geometry size smaller.

If you do not need a smooth gear, do not bother with subdividing it - this will improve performance while working with the gear in AC3D.

You also do not have to rely on subdivisions to smooth out the gear. you could create a smoother/beveled initial tooth and replicate that --- that gets more complex, however, and is outside the scope of this tutorial.

Also, if you want a non-spoked "inner" section, you could make it a lower-poly circle that isn't necessarily attached to the outer tooth ring.


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All content Copyright © 2006 Dennis Hawthorne, except where explicitly noted
supercoldmilk © 2006 Dennis Hawthorne