Hi,

I'm investigating a potential issue with my Bregant HB grinder (same as Pavoni Zip), where I think that the burrs might not be aligned properly. When grinding at fine levels, it makes a "chuff-chuff-chuff" sound that would indicate that there is some unevenness in the alignment between the burrs. The grinder works ok, but I could expect that it could perform better.

As a first step I took photographs and compared between running and non-running.



There are some smearness in the edges but not very much, but on the other side, i guess its very small differences that counts in the alignment.

To determine if there is at a certain place, I painted the edge of the top burr and ran with the grinds just touching each other:

The burrs after a short run with contact.

I'm a bit confused by the last image, it seems like there is a short region where the lower burr touches more, but with some variation around the burr. If its only the angle between the burr (motor axis) that is not perfect I would expect a section with paint removed and the rest untouched. The burrs are new, but it's the same sound with the old burrs.

What could be going on here, skew grinder burrs? A combination of several misalignments?

Is there anything that can be done to correct misalignment of the burr axis?

Regards

If the paint test shows burrs are touching all round when the motor is not running, the static alignment is good, and the burrs are fine. An uneven sound could mean the whole assembly is wobbling while running. Unfortunately, I don't recall anyone ever posting tips for diagnosing something like this.

Just exactly what leads you to think the grinder could be better?
Does the grinder vibrate when run empty?
Unplug the grinder. Pick it up and shake it. Does it feel like the motor could be loose?

!!! Upper carrier removed and grinder unplugged !!!

Can you feel any play in the spindle when you grasp the nut. Try NSEW, rotate the burrs 120° and repeat.
There should be no play.

Clean the burrs to remove any stray coffee. Install the upper carrier and turn it down to hard Zero and note the position, back off 1/4 turn. Now try moving the upper carrier NSEW. Can you feel any movement? Back out 120° and repeat 3x

Find the soft zero where the burrs contact while running. Note location.
Any large difference between hard and soft zero?

another_jim wrote:If the paint test shows burrs are touching all round when the motor is not running, the static alignment is good, and the burrs are fine. An uneven sound could mean the whole assembly is wobbling while running. Unfortunately, I don't recall anyone ever posting tips for diagnosing something like this.

I did a slightly different paint test then the one I now find on google. I painted the top burr with a felt pen, and ran the grinder with the burrs just touching. So the unpainted areas are where contact has been and wore the paint off.

Maybe I should do same experiment with bottom burr.

Many thanks for the feedback, very appreciated. First, the grinder works and gives fully drinkable coffee so maybe I'm just chasing ghosts in the search for a better cup. But I'm an engineer and prone to try to improve things

The burrs are however not parallel, when turning the spindle by hand one can feel some sections when friction occurs and some without, near my normal espresso grinding level. (The spindle has no free play NSEW.) This might not be an issue, but i would imagine that it gives an uneven grind.

The machine is a second-hand, former cafe machine (now made doserless and custom hopper) with new burrs. The new burrs are according to the shop original Bregant=Pavoni Zip=a bunch of grinders. The fitting of the burrs where not perfect, original had better fitting. Had contact with Bregant Italy and according to them the specification of the burrs are the right for my machine. The original burrs (with a half a mm smaller inner diameter) do however also have the "non-parallel" issue.

And I would think that one or more of the three wipers/slingers shown in your first pic would come into contact with the surface of your adjusting housing marked with X's below:

Sorry, I am not sure I understand this? Note it's the top burr with adjustment house on the picture. Do you mean that the three wipers in bottom touches the top house before the burrs get into contact?

Thanks,

After some messing about with the grinder I have maybe come to some understanding.

I tried the difference between the soft zero (first touch) and hard zero (which I interpreted as a "stop" where no turning of the carrier is possible, motor not running!). It was about 90 degrees difference. I could "feel" that the grinders touched over a section at soft zero. My conclusion was here that either both carriers are misaligned or the burrs skew.

I removed the (new) burrs, they were perfectly flat and smooth when held to each other.

I disassembled the grinder and tried to see misalignment in the burr holder, but very difficult to identify it. I put the old burrs on (and didn't lock the screws very hard). When rotating it was visible that it was not perfectly centered, but the alignment (how parallel they were) looked good. I assembled grinder again, and problem is much less. Instead of 90 deg between soft and hard zero, is now maybe 20 deg and the chuff-chuff sound is gone.

I see two possibilities of what was wrong:
* The new burrs fit but the holes in the carrier are not as well aligned as on old burr
* I had tightened the burr screws too hard, by some reason not understood by me there's a gap between the inner burr section and the carrier.
Both these would skew the burrs is my kind of conclusion, but I also have difficulties believing the burrs can get skewed, they look and feel very robust.

A bit confused but the result seems better..

Espresso distances are very small, on the order of 1/100mm. It's most important when changing burrs to first determine the the burrs are true. A simple way to do this is to place a truestraight edge across both burrs sat side by side on a true flat surface, preferably backlit with a window or lamp. There should be no gap or change as each burr is rotated.

Once it's determined the burrs are true, the grinder must be surgically clean.

Install each burr, turning the screws until they just stop. Gently snug up each screw in turn until the desired torque is reached.

Check the hard and soft zero. If they vary drastically, try rotating one burr 120° until satisfied.

See Burrs, Carriers, Micrometers & Math OR Why some [KA] grinders s*ck