Thanks to AOL06 and aleung for the original designs. I started with aleung's design as a base but basically remade it from scratch.
I don't think a plastic guide would survive a drill bit anyway so I have omitted this function. To that end I also shortened the 'guide' which now functions as a dust shield which should deposit the dust into the bowl below. Additionally the center hole is now 15mm so you can fit up to a 13mm drill bit.
I have increased the fillet in the bowl for easier cleaning, and chamfered or filleted everything for pretties.
The bowl also ended up slightly smaller by the end of the process.
Disclaimer: I have not printed this, please let me know how it goes.
Edit: Added a V2 without the bevel on the back as suggested by kickasskingy.