Update 3: DIY Hario conical burr grinder Kitchenaid stand mixer attachment

Probably final update to the previous 3D printed design is here.  (No change to the previous bearing adapter piece design.)  You can also order these designs essentially at cost here.  The main changes are there are now 3 set screws in the adapter instead of 2, and the square bit has chamfered corners to help it go into the hub a bit easier.

With the additional set screw, I have been using this piece intermittently for over a year without it wearing out.  Please note that I believe this can put stress on the KitchenAid motor if you are trying to do a very fine grind or if you are using harder coffee beans (e.g. light roast).

I've been using this with both my larger and smaller Hario burr grinders.  For the small grinder with the pentagonal driver, I found a stainless steel adapter available here.  There are other sellers with similar items; I don't know whose design was first but this seller is amiable.