I made this design in Onshape, see the different views in the picture. After printing you have to remove some helper material.

You have to turn the print in your slicer by flipping the z axis. Scale down to 40 or 60 %.

You can edit some parameters by copying in your own free onshape document:
https://cad.onshape.com/documents/57da72ee2055a913a82c3160/w/37820ef0c2207e80fb224e86/e/171e37f48a96fab4dd899188

Please leave a comment.

Here is a preparation video.
https://www.youtube.com/watch?v=rmZo3sw1wwk