spencerwebb wrote:I like your style mate, I have also thought about this and used it on an old grinder to great effect. I'm too scared to do it to the EK for reasons mentioned here but I do have my old coffee burrs sat around doing nothing.

Is there any mileage in mounting the burrs face down and then running them together or would that just make things even worse, my head can't work it out.....

I really is one of my main bugbears with grinders. It seems to me that the burrs should touch all the way round and if they don't then you are potentially grinding way off the mark by espresso standards.

Unless the carrier is absolutely parallel, you're not creating an equal gap, just narrowing a gap that already exists. The fixed burr will end up ground at an angle and the rotating burr will be ground more or less even. The increased ability to grind fine that the OP noticed was because the burrs were ground down so that the extreme outer tooth depth was reduced. If you were to continue running the burrs together with force applied to them, eventually you would grind away that tooth gap completely and the burrs would cease discharging grounds. This could happen quite quickly if the burrs were perfectly parallel or may take some time if alignment is skewed.

If the burrs were held to absolute parallel and touched all the way around, grind uniformity would be extremely tight. Most grinders are nowhere close to absolutely parallel, and I suspect this is where a lot of our "bi-modal" pocket science comes from. One side of the burr is chucking out large grounds and 180* away the grounds are much smaller. It doesn't take much deviation in tolerance to make that happen. Bulk grinders like the EK seem to excel at holding the burrs very parallel and their grind profiles seem to reflect that. Warning: There was a lot of speculation in this paragraph.

Don't get me wrong, I can exactly see what's happening here, we are essentially messing the burrs up but you are assuming that the factor that affects the grind size is a gap that we are in some way depleting. This is not how I visualise it (probably incorrectly!). On the EK burr there is a large flat surface with a tooth on it. Since the burrs are not touching (or shouldn't be) when we are grinding espresso it is surely the distance between these flat surfaces that creates the final particle size and nothing else. the rest of the burr is just teeth, chopping the coffee smaller and smaller until it can fit out of the outer edge. This would lead me to believe that if these flat surfaces were the same distance apart all the way round, even if the teeth were slightly different heights, then your grinds would be more even.

Almost certainly more speculation and pocket science (READ BS) than should come from one person in this post for sure!

Interesting topic for sure.

endlesscycles wrote:I'm also an engineer. The edges affected represent an inconsequentialy small portion of the total... Say five to ten degrees of three sixty

If the EK doesn't grind fine enough for a proper flow rate, then it is an alignment problem.
Reducing pressure and various tamping technics might help to "compensate" it.

The bigger the burrs the harder it is to get them parallel.
The bigger the gap between grind setting and zero, the more parallel are the burrs (with the same thread pitch)

On other grinders I agree with you, if they don't grind fine enough without being in negative zero, it is better to let the burrs touch / chirp instead of throwing the grinder away.

Under the blind the one eyed is king and this is how the output will be. (one eyed)

Terranova wrote:The "inconsequential small portion of the total" is the most important part for the output and particle size distribution. (imho)
I am not an engineer though.
If the EK doesn't grind fine enough for a proper flow rate, then it is an alignment problem.
Reducing pressure and various tamping technics might help to "compensate" it.

The bigger the burrs the harder it is to get them parallel.
The bigger the gap between grind setting and zero, the more parallel are the burrs (with the same thread pitch)

On other grinders I agree with you, if they don't grind fine enough without being in negative zero, it is better to let the burrs touch / chirp instead of throwing the grinder away.

Under the blind the one eyed is king and this is how the output will be. (one eyed)

Hi Terranova, have you ever corrected this on an EK? Any thoughts on how you would go about doing it?

spencerwebb wrote:Don't get me wrong, I can exactly see what's happening here, we are essentially messing the burrs up but you are assuming that the factor that affects the grind size is a gap that we are in some way depleting. This is not how I visualise it (probably incorrectly!). On the EK burr there is a large flat surface with a tooth on it. Since the burrs are not touching (or shouldn't be) when we are grinding espresso it is surely the distance between these flat surfaces that creates the final particle size and nothing else. the rest of the burr is just teeth, chopping the coffee smaller and smaller until it can fit out of the outer edge. This would lead me to believe that if these flat surfaces were the same distance apart all the way round, even if the teeth were slightly different heights, then your grinds would be more even.

Almost certainly more speculation and pocket science (READ BS) than should come from one person in this post for sure!

Interesting topic for sure.

If the burrs were parallel, particle size would be even assuming this method were to grind the burrs into perfect tolerance. Since they are not parallel, one section of the fixed burr will have bigger teeth than the location 180* away. Mashing the burrs together doesn't make this gap even out, it just reduces the overall depth of the teeth.

spencerwebb wrote:have you ever corrected this on an EK? Any thoughts on how you would go about doing it?

No and I couldn't.
It was just a matter of luck with mine.

I guess with no absolute proclamations being made, we're all safe to speculate. And these ideas I'm having as well as others might work, they might be a wasted effort. If the run out could be measured and you happen to find that your particular grinders mounts and shaft are very true, then could someone just take both (new) burrs, and modify them manually?

I've seen people sharpen woodworking planes by taking a sheet of glass, spraying it with water and letting an ultra fine sheet of automotive sandpaper (3000 grit +) on, then using a mount to hold the piece securely while they work on it. I'm probably just pissing in the wind guessing, but I wonder if you could improve the terminal edges parallelism with something similar, given that you have a properly aligned mount and shaft. I imagine one could flatten the very edge of the burrs without completely obliterating the teeth, and have a tighter level of precision in the entire circumference of the burrs edge by doing something like this.

I'm not going to do anything to mine when I get it back together, other than set it up and run plain, stale beans thru it first, then proceed to use good coffee. But it will be an interesting thread to follow and see if someone learns something worth sharing. I don't see any reason to make something more complex that it needs to be. I might be perfectly happy with these burrs in this grinder without any tweaks.

TomC,
You are nearly on the solution...
If, as suggested, the issue is infact that the burrs themselves are the cause of the uneven contact (and the shaft, carriers, etc are all correctly aligned), then yes the solution is to correct the burr problem....but not on the working face !
Shimming, scraping or ideally "lapping" the mounting face of the defective shims is the fix...
...but I am more than a little surprised that Mahlkonig would produce a burr with any significant parallelism error, and would look long and hard at the mounting surfaces for dirt, dings, damage etc before doing anything else.

I went ahead today and throughly cleaned out my EK and recalibrated it. I didn't go as far as Marshall, just tightened up the finest setting and allowed a mild "ringing" rather than any major rubbing. I can now pull shots quite a bit tighter than required and have stopped nutating and updosing, even with city roast coffees. I am currently at around 6.5 bars (7 measured with a gauge), but I'm going to try pulling with a bit more pressure. I'd suggest all EK owners go ahead and recalibrate after running a decent bit of coffee through the grinder, since the ideal zero point will change, and a broken-in grinder should be able to provide espresso-size particles when calibrated properly.