Lost a car key button? Photoshop is the solution for a quick fix

When a friend lost the Unlock button from his car key, he asked if I could 3D Print him another one. The print itself would be straightforward, of course, but how could I accurately reproduce that curious shape – a trapezium with highly rounded corners? It would be difficult to draw using a standard CAD application, requiring a series of accurate measurements; and I’ve no idea how I’d go about measuring the radius of those corners.

The simple solution: Do it in Photoshop. It may seem unlikely that you’d want to use an image editing application to create a 3D object, but it turned out to be the perfect choice.

1. Photograph the hole

As a first step, I took the key fob apart and photographed the hole that needed to be filled. The photograph itself didn’t need to be anything special, so I just snapped it with my iPhone:

2. Draw the shape

Although you can extrude 3D objects in Photoshop from pixel-based layers, you get better and smoother results if you extrude a path instead. Use the Pen tool to draw around the inside of the hole.

You’re following the photographed shape, it’s easy to create a path that exactly matches it:

3. Extrude the path

Use Photoshop’s 3D panel to turn the path into an extruded object. It’s a straightforward process: all you have to do is to make sure Work Path is selected from the pop-up Source menu at the top of the panel (it will default to extruding the current layer, otherwise).

Then make sure 3D Extrusion is selected – it will probably be selected already – and hit the Create button at the bottom of the panel to produce the extrusion. Right away, that path will be turned into a real 3D object that you can spin around and view from any angle.

As with all Photoshop extrusions, it will appear in the wrong orientation. You’ll need to select it and use the Coordinates tab of the Properties panel to rotate it 90 degrees around the x axis, and then click the Move to Ground button at the bottom of the panel so that it sits firmly on the ground plane, ready for printing.

It’s likely that the button will be extruded much too deeply, though, as the default is to produce a much squarer object than you want.

4. Scale the extrusion

Use the Extrude control to lessen the amount of the extrusion. So far, no measurements have been set, so it’s largely a matter of gauging the extrusion amount by eye. There’s nothing wrong with this; although you could apply accurate measurements at this stage, because it’s only a ten minute print it’s a lot easier just to print one out and then modify it as needed afterwards:

5. Add a flange

The button as it stands is all very well, but there’s nothing to stop it falling out of the hole and getting lost – which is exactly what happened to the original button.

To solve this, make a copy of the object by selecting it in the 3D panel, then use the pop-up menu to Duplicate it. This will make an exact copy of the original object:

After you create it, it will look as if nothing has happened. That’s because the copy is the same size and in the same place as the original, so it will appear that no change has taken place. When you look in the 3D panel, though, you’ll see the additional object listed as Layer 1.1 beneath the first.

6. Flatten and stretch

The duplicated object will be exactly the same size as the original, of course. Use the 3D axis controls (or the Properties panel if you prefer) to make it much shorter, then make it a little longer and a little wider so that it projects beyond the original object.

You’ll need to use the Move to Ground button, also in the Coordinates pane of the Properties panel, to make sure the button is sitting flat on the ground plane:

7. Set the scale

Choose 3D Print Settings from the 3D menu, and take a look at the Properties panel. Here, you can at last set the scale of the printed object.

The default measurement settings are for pixels, so you’ll need to change this to either millimetres or inches, depending on your preference. do this using the pop-up Printer Volume menu within the panel.

All you need to do now is to physically measure the longest part of the opening in the key fob. I found this to be about 21mm, so I set x dimension in the Scene Volume field to 20. This was to allow a 0.5mm clearance all round, so the button didn’t get stuck in the hole.

The other two dimensions are calculated automatically from this – you can see that it produces a y dimension (the height) of 5mm, and a z dimension (the depth) of 11mm.

8. Print to STL

Choose 3D Print from the 3D menu, and you’ll see a print dialog. If you have a compatible 3D printer connected you can just go ahead and print directly from within Photoshop; if not, you can export an STL file and then use your favourite slicer to turn it into a Gcode file that your printer will be able to read.

The end result: a perfectly formed button that exactly matches the opening in the key fob.