Weekend Build: 3D Printed and Customized Shift Knob

For the longest time, I wanted to have a really cool shift knob for my car, and for most of my life, any of the cars I have driven have been automatic and utilize a trigger to disengage and shift gears, which limits my ability to easily swap out the shift knob for something different. I knew manual transmissions would have it easy since usually they’re just screwed onto a threaded shaft. As luck would have it, the car I have now is automatic but doesn’t use a trigger to shift which means I can create whatever knob I want, screw it on, and have that extra bit of flair to my car.

Method 1: One 3D Print, No Hardware

This first method is the easiest to set up, as all it requires is a single extrusion 3D printer and some filament; no hardware at all. To create this one, the first thing I needed to do was create the base shape for the shift knob; it needed to have a base larger than the diameter of the threaded shaft of the shifter and a handle that would fit comfortably in my hand. There are multiple ways you could go about modeling the base piece, but in my case, I wanted to use Fusion360 to get some nice curves to it.

Once the base was modeled it was time to figure out what design I wanted debossed into it. While I could use the reference canvas tool to bring in a logo, it was actually a lot easier to use MatterControl for this part. I exported the base from Fusion360 and imported it into MatterControl, then started modeling on top of it. A cylinder set to just slightly smaller than the threaded shaft needs to use the Alignment Tool to center it on X and Y and put at the bottom of Z. I want this cylinder to be slightly smaller than the diameter of the shaft so it can tap into the plastic and maintain a good grip on it.

With the Image Converter Design Tool I could turn an image of a flame into an extruded 3D model. Then with the fit-to-bounds I can set some constraints so if I want to go back and change the image, it won’t ruin my settings. some alignment tools, I could center it and extend it into the shift knob. Using the Subtract Tool, I can select the Fit-To-Bounds and subtract it from the main body while maintaining its spacing. Should you have a dual extrusion 3D printer, you can also use Subtract and Replace to have the intersection of the design and the knob be marked as using a different material, so you can dual extrude it.

And there we go! A shift knob using a single extrusion 3D printer ready for printing and installing.

Method 2: Multiple prints, some hardware

Sourcing the hardware is easy, but determining the threading can be annoying. My first suggestion would be searching online to see what other owners of this car have identified the shifter’s threading, barring that you can also take your shift knob into your local hardware store and see what bolt threads into it properly. In the case of my car, an M8 lock nut was the right fit. Make sure you get a lock nut, otherwise your shift knob will be able to spin too freely.

Much like before, I modeled the base in Fusion360. This base can also be found on Thingiverse as designed by Wills World, but I needed a clean 3D model to embellish with my own designs and to change some of the hole diameters, which is why I remodeled it. Since my personal printer can’t print two materials or colors at once, I couldn’t do a Subtract and Replace like mentioned before; I’d need to do things a little differently. First thing was to create a hole for the nut to sit in, sized just barely larger than the lock nut. It’s better to have this a tight fit and need a vice to press it in rather than loose; a loose nut means your shift knob will have some wiggle to it.

On the lower half, I made sure the hole was easily larger than the shaft diameter to make sure insertion is easy and on the upper half, this hole will accommodate the shaft as it screws through the nut.

To create the design in this one, I did the same as before: imported the top half of the knob design into MatterControl and used image converter and the align tool to place the design on the face of the knob. Then rather than just subtract the design as I did for the single extrusion method, I can instead use subtract and replace. The difference between the two operations is subtract and replace will subtract a mating chunk from the first part, and then where they were intersecting leave that as a new model, which is perfect for seamless dual extrusion. And now that I have it modeled in MatterControl, I can really get creative. If I want to quickly jump between different images on the knob, all I have to do is change the image and some settings in the image converter and save that as a new version. This way I don’t need to manually retrace a logo every time I want a different one.

With this specific design, I really wanted to put some nice finish and polish on this 3D print, so I went ahead and sanded it to smooth it out. I first started with some 120 grit to break down most of the layer lines, and then 220 to clean up the deep scratches of 120. I followed up with 400 and 800, using some water to wet sand for a much smoother surface and finished it all up with a couple coats of gloss clear coat.

To attach this knob to the post in my car I sandwiched an M8 lock nut inside the two halves of the printer knob. 

You can even experiment with different finishes on the knobs depending on the material you print. Since this is going to be in a car, which can easily get hot enough to deform PLA in the right conditions, printing in PETG, ABS, Nylon, or annealed Tough PLA is the right choice. For a more textured feel, a dual NylonG print gives a professional appearance, or ABS that’s been sanded smooth and clear coated can make for a great glossy finish that’s hard to tell was even printed.

And there we go! With either of these designs saved into MatterControl, I can endlessly change the designs to better fit my friend's and families' personalities and interests. There's definitely some things that can be learned here and there, like trying to print at lower layer heights or a smaller nozzle size to get a cleaner print which would just make for a much better finished product. If you make a shift knob for yourself, I'd love to see it!

Happy shifting!