Adding fine adjustment screw to Bunn/update

Grinders are one of the keys to exceptional espresso. Discuss them here.
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#1: Post by DJR »

It's now been a year of daily use for drip and sometimes use for espresso. Sometimes someone posts a "great idea" and you never hear any follow-up.

The fine adjustment screw works very very well. I have not yet a-b'd it with a high end espresso grinder but will soon. It certainly delivers good quality espresso for me and allows an instant change to drip and back again to the same exact spot you left it when doing espresso.

For drip, retention is zero. For espresso it varies but can be as much as two grams/40 grams of beans. None of the retention is in the grind chamber. It gathers around the last bit of the exit area. I'm going to try to solve this problem.


The Bunn adjustment screw is chrome plated brass. It has a bearing on the end which presses the spring loaded burrs together to adjust the distance between them. The screw is about 12 TPI which allows one to very quickly move the burrs from coarse to fine. That's good, but to fine tune the burrs for espresso it's problematic for two reasons.

First, the detents are far apart, so finding and returning to the exact place you were before is really not possible if it falls outside of the detents.

Second and as important, making micro adjustments is very difficult and very unrepeatable.

The solution is pretty simple and is one I've used in the past for allowing both a fast and a fine tracking adjustment to my homemade 72" belt grinder. i believe this approach is used on other machine tools and at least one coffee grinder.

1. Remove screw and pull bearing off screw.
2. In a metal lathe, remove the post on the end of the screw that held the bearing, leaving a bit of flange as a place the bearing could rest on.
3. Drill a 3/8" hole into the screw, about an inch.
4. Drill a 3/16" hole through the screw, leaving about 1/4" at the end (facing the front of the grinder).
5. Drill and tap an 8-32 thread through that remaining 1/4".
6. Make a post out of 3/8" SS that will fit into the screw and on the end of this post reduce to fit the bearing.

So now we have a moveable bearing that can be moved by either the main 12 TPI screw or fine tuned using the 32 TPI screw, which give quite a bit more resolution and precision. You can go from drip to espresso in a twist of the wrist. When dialing in the espresso, if you start from a detent and then use the 32 TPI screw, once you get there, you can basically toggle from drip to espresso and back and get to the same place each time repeatably.

I made a couple of these and it's not a huge job. I need to test them for a couple years to say definitively that they amazing, but I can say that the Ditting Burrs do work for espresso, repeatably. I will put a large knob or handle on the knurled screw so that adjustments are even easier and in smaller increments.

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#2: Post by TomC »

Finely you talk about it!

These are awesome.
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DJR (original poster)

#3: Post by DJR (original poster) »

A larger handle will make a big difference in fine adjustments. I'll do it this weekend.


#4: Post by Uldall »

Nice job ;-)

Coffee Driven.


#5: Post by bakafish »

Nice job. :D

I also thought similar ways on my Mahlkönig Guatemala since I saw the photos of the EK43 Barista, but I tried to grind 17g beans with the finest setting which the burrs were just untouched. The grounds were very fine, but it just reached 25 seconds to get 34g coffee on my Portaspresso Rossa PG with IMS B66 basket and 9 bar, so I decided not to mod it although I felt the best shot was with 6~7 bar when used the Guatemala.

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#6: Post by happycat »

Fantastic. If the CDN dollar weren't in the crapper I would love to upgrade to the Ditting burrs and try this. Lighter roasts are tougher to grind on my Pharos. Great job.
LMWDP #603


#7: Post by CwD »

I really like this idea, and am definitely considering trying it.

I was trying to thing of some way to do it for a while, but it seems that for espresso "as close as possible without chiming" has produced the best results, and if it could get just a tiny bit finer that be nice. So it almost seems a bit pointless after some use of the Bzilla for espresso. Then again, it could let me get the burrs closer than with ordinary zeroing alone.

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#8: Post by bostonbuzz »

Excellent work.
LMWDP #353

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DJR (original poster)

#9: Post by DJR (original poster) »

Mitch is correct in that the space between the burrs rubbing and espresso grind is pretty small. However, with the screw it is possible to get very very close and still be able to adjust. My tests have been with 15.5 grams in a MCAL basket. If I went to 16.5 grams it would definitely choke the machine. So this gives you kind of an idea. I could go to 17 grams and back off the screw a bit, giving me more adjustment latitude. That's why I need time to really see if it's a great solution.

In theory, the large burrs, along with the ability to instantly switch between drip and espresso seem great. But I'm withholding final judgment. The time to grind 15 grams is very fast. And the retention, though I haven't measured it over dozens of shots seems less than .4 grams.

BTW, the retention in drip is 0 grams. I put 40 grams in every day and get 40 out. Every day. I removed the chute assembly entirely, as this is definitely where the retention occurs. It does not occur inside the grind chamber. I'm quite sure of that. The espresso retention does not occur in the grind chamber either, but in the bit of built in exit area right before it would have gone into the chute.


#10: Post by JohnnyCupcake »

Looks good.

Might have to give it a go on one of my Bunn's