I've designed a new exit chute for the DF64 to address retention and static issues with the stock grinder. I imagine this may be of interest to readers that either have a 3D SLA printer or know someone that does. There are a lot of makers out there, and I bet most of them drink coffee.

After cleaning my DF64 too many times, I made a couple observations:

1) The closer I held the catch-cup/portafilter to the exit port, the more debris accumulated on the grinder. If I set a bowl on the counter, well away from the exit port, I saw far fewer grounds accumulate around the exit port. My theory is the static 'spray' force is largely between the individual particles of the grounds, and the accumulation around the exit port is simply an aftereffect of the grounds self-repelling. I tried charging the portafilter to about 3KV to see if I could electrostatically attract the grounds, but the grounds were too busy avoiding each other to react to the charged portafilter - besides, the safety issues of a 3,000-volt portafilter would be, well, problematic.

2) Grounds were semi-permanently accumulating and lining the direct path of the exit chute. Between what gets backed up behind the clump crusher and the nooks and crannies of the factory stock exit chute, there could be up to a couple grams of fines and oils that could break loose and make an unwanted contribution to the grinder output - yum. I think root cause is from pressure fluctuations along the path of the grounds: high-pressure at the clump crusher, low-pressure at the top of the factory exit chute, and increasing pressure as the exit chute narrows. This creates pressure pockets that encourage grinds to accumulate.

I addressed the observations in two ways:

1) Redesigned the exit chute so there is a constantly-increasing cross-section along the path, from the spinning rotor to the exit port. Any pressure build-up in the port will find the path of least resistance to be in the direction to the output:



This reaches into to grind chamber and clears the rotors by just a half-millimeter. The elliptical aperture is about 40% the area of the original opening, and similar to the opening of the original design after a build-up of coffee grounds. Lest one thinks this is choking the path of the grounds, the velocity of the grounds exiting the chute is noticeably faster than the original version with the clump crusher.

This new chute drops right into where the clump crusher and factory exit port went - that's right, no more clump crusher!



The new chute extends a bit past the cover plate, and incorporates little magnets for attaching the next half the redesign:



At this point I have a new exit chute that no longer accumulates old coffee grounds. It completely clears with a light tap on the bellows - no more pumping.

However, coffee grounds will still drift around and stick to the grinder and surrounding countertop. So the second half of the solution is to control the space the grounds pass through with a magnetically-attached downspout and expansion chamber that extends into the dosing cup (or portafilter).



As with the bellows, a single light tap on the wall of the expansion chamber will knock loose any grounds in case I was too light with the RDT. My countertop is now spookily clear of grounds as if I wasn't using the grinder every day.

Not missing the clump crusher. Grounds are now significantly fluffier, to the point where I had to use a taller dosing ring on my portafilter.

If there's any interest, I can post the design files online (Thingiverse, GrabCAD).