Here are models of the shafts of EC11 flat shaft and EC12 shorty rotary encoders, commonly used in the custom keyboard hobby. I've added a 1° draft to each shaft to make the fitment easier. Just grab your preferred format, bring it into your preferred CAD program, and subtract it from your model!

Note: For EC11 knobs, you may with to put an 8.5mm diameter hole in the bottom of the model below the shaft cutout, to give your knob a skirt that covers some of the lower section of the encoder itself. See the example model I included if that sentence isn't clear to you.

The models are also available as Onshape documents, so you can just hit Derived Feature button and use the Onshape shaft model directly in your knob design in Onshape! Other CAD export formats are also available there. Enjoy!

[https://cad.onshape.com/documents/871fb46db08a30afa56906d2/w/ab5090d1cc1b561fe6d59b19/e/083f99290afb1807d885f9be?renderMode=0&uiState=63d44461b3f80f4c9d986d5b](https://cad.onshape.com/documents/871fb46db08a30afa56906d2/w/ab5090d1cc1b561fe6d59b19/e/083f99290afb1807d885f9be?renderMode=0&uiState=63d44461b3f80f4c9d986d5b)