Screw Visualisation

I was asked to produce a photorealistic render of a new performance screw by my friends at KAL Group.  So, I thought I’d put together a bit of an overview of its construction.

I started out with the technical diagram of the screw (in the form of a PDF).  I used that to create a bunch of viewport images that I could use for reference when building the geometry.  One thing I had to do initially however, was correct the aspect ratio of the diagram – which was slightly stretched.  I was able to build a very accurate model from the diagram alone, however it wasn’t obvious how the underside of the screw head was constructed.

When I received the physical item, it differed slightly to the technical diagram.  I updated the model to take into account the differences.  Also, being an uber-nerd, I used a Veho USB Microscope to get a good close up of the screw.  If you haven’t seen a USB microscope, I recommend getting hold of one.  They’re quite inexpensive (around £40) and come in really handy for stuff like this.

Creating the body of the screw was relatively straightforard, however matching the thread to the technical diagram took a fair bit of trial and error.  To compound things, this particular screw had saw teeth towards the front, along with a semi-circular rebate cut out of the tip.  In the end, I lofted the thread onto a helix spline.  I then applied a series of loft adjustments to vary the width and size of the thread along the length of the screw.  Finally, I applied a couple of boolean operations to cut the teeth and semi-circle.  It was kind of like replicating the real-life sequence used to create the screw in the factory, with tools (boolean objects) applied in sequence to remove bits of geometry.

For the final image, the client requested that I extend the thread further up the screw – so the final version differs again from the physical screw:

Finally, rendering.  There are only two materials in the scene, both are metallic.  The final images were rendered at 4000 x 4000 pixels – more than enough for most uses.  A fair amount of manual clean-up work was required for the boolean areas (the sharp bit at the front!) both in the geometry and final renders.  The final images were a composite of diffuse render, with an ambient occlusion layer to enhance the thread.  I also added an alpha channel so the screw could accurately be extracted from the background.