Our front-load dryer has a plastic knob that recently broke. It still works, but is getting looser every week. Part of the plastic shaft (see lower left) has snapped off. This is apparently a common failure. And the reason for a dryer knob repair project.

Of course, I could just buy a new knob. I did some web searching and found a replacement with a range of prices of several sources, including Amazon at $70 and ebay at $20-30. Not cheap. Maybe I can fix this myself.

At first I thought about 3D printing a complete replacement dryer knob. I went looking for a model that I could print. The usual place to find things like this is Thingiverse. I could not find an exact match. But I did find a CAD model for something called a parameterized knob. This means that someone has made a generic model of a knob that can be adjusted using various parameters, things like width, height, shaft dimensions, and so on. So, printing a generic knob was one option.

Then I had a closer look at the old broken dryer knob. When Whirlpool designed this knob, they included a little metal insert that fits between the shaft of the switch and the shaft of the knob. It’s a typical “D” shape to provide support without the need to use a set screw. This insert is still there, and is what is holding the knob onto the dryer. Perhaps I could just print a collar to fit over the broken plastic shaft, and fit snugly around the metal insert. Properly shaped, a plastic collar should effectively fix the dryer knob.

Using CAD for dryer knob repair

Since it is such a simple and symmetrical shape, I was able to design a model for the collar in CAD. The broken plastic shaft has a 10 mm outer diameter. The distance between the inside of the plastic shaft at the top, and the broken edge at the bottom is 8 mm. So I extruded a cylinder with a 13 mm diameter and 10 mm long. Then I used CAD to create hole down the middle of 11 mm, i.e. just a bit bigger than the shaft. Finally, I had to add some material along on side of the hole in the collar, so that the collar would have the right shape to slip snugly over the broken plastic shaft and also hold the metal clip in place.

You can see the collar model on the lower right, and the final printed collar on the top right. The collar took about 3 minutes to print and consumed about 10 cents worth of plastic.

Now the collar fit snugly over the broken plastic shaft, and its flat side holds the metal insert in place, also snugly. And the dryer knob is back in business. The good news is that I saved money and now that I have the model designed, I am all set to fix the washer knob, if and when that breaks.

Another successful DIY repair. Thankfully easier than the last one I tried.