Even as a kid, I thought that the knob on our washing machine was janky, and I knew that whoever made it tried to use the least possible material. I distinctly remember that it even needed a little metal band around the column to keep it from breaking. Turns out, the little metal band only holds out so long.
So, as a somewhat competent adult empowered with free 3D design tools, I did something about it.
The goal here is a solid, 3D printed knob that fits over the existing selector pin - the 1/4" metal post with a flat side that destroys stock plastic knobs. I used 123D Design to make the knob model and then printed it on an Objet Connex500. Granted, I'm extremely lucky to have access to the printer, but the 123D line of apps is totally free, and I think the newest MakerBot can handle it!
Here is a model of the knob when finished. It's very simple, just meant to be a base on which you can make a custom handle. Click the "3D View" button at the bottom to see it in space.
Step 1: Dimension the Original to Recreate It.
First, let's look at the original. The manufacturer made them with lots of negative space to save production costs, but that severely limits lifespan. There's a lot of torque on the plastic and it eventually just snaps.
To start, take some measurements. I used analog calipers and found it had a 1/4" post with two little shelves that create the flat side - like a capital D. Yours may have different measurements (mine was actually about .24 inches).
The important dimensions are:
1. the overall diameter of the post
2. how much was taken off the post to create the flat side - it turns out that on this particular style, the flat side is created by removing 1/4 of the post diameter.
3. depth of the post - how far it sticks out from the machine.