First, we need to create the brush that will be used to help us create 3D like images.
Open a new drawing with white background, add a transparent layer, name it "top". I made my drawing 640 x 640px @ 300 DPI.
On the transparent layer, using the Ellipse tool, draw out an ellipse like shown:
Do not turn the ellipse selection off.
Create a new transparent layer and drag it under the current transparent layer, name it "band".
On the new layer, increase the size of the selection (Select - Grow) by 3 px.
Select the Move tool, set the move to selection:
Move the ellipse selection like shown:
Now the fun begins. You can opt to save the new image as a brush shape - or - just use a copy of the shape by selecting Edit - Copy. To minimize the selection area of the new shape, I use the Rectangle select tool to enclose a larger portion of the shape, before copying it:
Open a new drawing with a white background. Add a new transparent layer, name it "base".
If you have decided to just copy the shape from the first drawing, and not save it as a brush, save that drawing as shape.xcf and leave it open to be re-used for copying when needed.
Select the Airbrush tool and make sure your tool option settings are like the following:
With the Airbrush scale at 1.00, click toward the center of your image to set the initial brush image:
Create a new transparent layer, name it "donut hole".
Using the Ellipse tool, center an ellipse and then run a reverse gradient with the Blend tool, like shown:
Reduce the brush shape size to about 25 and then create 3 grooves, like shown:
Use the Ellipse select tool to trim the bottom of the grooves by creating a selection that matches the bottom of the base, then Invert the selection (Select - Invert) and press DELETE.
Now we're going to use the shape brush as an eraser, be sure to set the Eraser scale to 25, same size as the grooves. You will need to erase the bottom portion on two layers (Grooves front and Base) the same exact way. See below:
First the grooves front layer, then repeat on the base layer:
To complete the gear solid, select the Base layer.
Now select the Eraser tool again, with the brush shape as the selection. Reduce the scale to 20 (we need to make the back grooves slightly smaller to account for depth). Trim any grooves that don't line up correctly using the Rectangle select tool (note the front left groove's outer edge):
Create a new transparent layer and name it "grooves back". Move this new transparent layer beneath the base layer.
Using the Rectangle select tool, line up selections for the back grooves and fill them with gradient using the Blend tool, like shown:
Finish the remaining grooves:
Have fun decorating or adding to your gear wheel and THANK YOU for stopping by! :)