All this talk about 'burr alignment' and 'tolerances'

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chopinhauer
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Postby chopinhauer » May 21, 2017, 11:25 pm

I've got what I believe is a bona fide question which no amount of googling has thrown up a clear and unambiguous answer: burr alignment and tolerances? Yes, there is a lot of info out there and on here, but nothing that I can get my head around.

By way of background, I'm one of the growing number (on HB at least) to have purchased one of the new breed of electric single dosing grinders, in my case the Monolith Conical. And like so many I'm totally blown away by this grinder's performance. To put it bluntly, in my long espresso voyage this has been the biggest step up and forward I've ever taken; bigger than moving from my Rocky to the Mazzer Mini-E or the Pavoni Europiccola to a Cremina. Way bigger! And I'm wondering why?

It seems from the discussions around these boutique or custom grinders such as the EG-1, Monoliths, Titus or modded Versalabs that a lot of this comes down to what people in the know refer to as 'tight tolerances' and absolutely precise burr alignment (on top of, of course, other design choices to optimise performance which vary from grinder to grinder such as burr sets, grind paths, materials, motors). My question is what does this really mean? I ask because it clearly does mean something and the apparently new attention to such things is changing the game in such a way that there is no going back.

Specifically what does precise burr alignment mean? Or really, the opposite? What were the best of the grinder manufacturers prior to this trend doing (Robur E, Major E, K10, K30 etc)? Were they not aligning their $2000+ grinders properly, or optimally? Is it just a question of attention to detail which 'little guys' like Douglas Weber, Craig Lyn, Frank Durra and Denis Basaric do (and can afford to do) vis-a-vis the big guys, Mazzer, Compak, Mahlkonig et al. And the same goes for 'tolerances'. What are they? And is it just a case of small, obsessive (and quite expensive) verses big and made to a budget? Or is it a fairly fundamental shift in approach to designing and making grinders? (I realise there are other possibilities and analogies such as the relationship between factory and custom modified cars; like AMG is to Mercedes etc).

Forgive me if this sounds like a dumb set of questions. I'm not a technical or even terribly 'handy' person, but I'm seeking an answer which clearly has a lot to do with practical and technical knowledge. For example, re burr alignment: I've changed burrs on numerous grinders and am now wondering if really the operation was as straight-forward as I thought at the time. Should I have also been aligning them in some way? Or were the alignment and tolerance aspects out of my control in a way in which they are not in regard to, say, the EG-1 (see http://lynweber.com/products/eg-1/care/alignment/).
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aecletec
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Postby aecletec » May 22, 2017, 12:17 am

I'm not sure at what level you're asking... e.g. if a burr isn't aligned well then the gap between them varies when it rotates ... e.g. think of a wobbling tire. A consistent gap will enable more consistent particle sizes. Espresso particles are very small and so even tiny differences in burr gap can make a big difference.
Or are you asking precise measurements?
The way I think of it, mass market production trades off on time spent on each grinder to maximise profit margins. When companies are already running at full capacity, why make it more expensive for themselves when close enough is good enough for the vast majority?

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RockyIII
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Postby RockyIII » May 22, 2017, 12:44 am

In Matt Perger's video, he uses a double thickness of aluminum foil as a shim when aligning a burr. I think that is only about 0.032mm (0.0013") thick, which seems like a very close tolerance to which he is adjusting.

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Postby samuellaw178 » May 22, 2017, 12:50 am

I'm no expert but have spent more time than I should on HB... :oops: will try my best to explain what I've digested so far..

Think of coffee grinding as a form of gap grinding. What that means is, during grinding, you bring two grinding discs close together to form a small gap, just enough to allow coffee particles smaller than the gap to pass through. By increasing/decreasing the size of this gap, you can control the coffee particle size you get.

Let's use flat burrs as example to explain the 'alignment' concept.

Imagine you have two round flat grinding discs and you overlay the discs on top of each other. Now, move the top discs up into the air by 0.3mm. If you do it correctly (and parallel-ly), the gap size between the discs should be exactly 0.3mm around the entire circumference. If you accidentally tilt the top discs by a few degree, now your gap will be uneven (say 0.1mm on one side and 0.5mm on the other side). This gap size affects your grind uniformity because as above, the gap size determines your grind particle size .

Another thing that could go wrong - the two flat dics should be completely concentric to each other. Meaning that when the two discs are overlaid on top of each other, you wouldn't be able to see the edges of the other discs when looking from the top/bottom.

These(above) are what is usually referred to as burrs alignment.

Once you have two burrs perfectly concentric and parallel to each other, you need to rotate one of the discs to grind coffee. This is another source of error that can affect the gap size. In case the axis of rotation is not in the center, or a poor motor shaft, your burrs will have run out and that will appear wobbly visually.



Tolerance is just a manufacturing concept. Manufacturing is never perfect. If you order 10 rods cut to 10 cm length, you never get all of them cut to 10.0000 cm. Some of them will be cut to 10.1 cm, some will be cut to 9.9 cm, and many others will be cut to between 9.9-10.1cm. The tolerance is 0.1 cm in this case. In the manufacturing process of course there will be some rods cut to 10.3cm or beyond, but that would be considered a reject and will/should never reach you. Depending on the situation, you can usually specify the tolerance needed (if the application requires 0.01cm instead of 0.1cm). The lower the tolerance allowable, the more expensive it is (higher chance to get out-of-tolerance rejects, and the cost has to go somewhere).

The thing with tolerance in grinder is, there is no universally acceptable tolerance. I recall Versalab has a runout tolerance of around 0.3mm. Mazzer claims to aim for 0.02mm. Frank I think he aims for 0.01mm. But as far as I know, measuring the actual tolerance is very time consuming and very tricky because it has to be measured once everything is assembled (at least for the parts affecting the gap size). Thus it is almost impossible to do it at large scale manufacturing.

Another catch is, because a grinder is made of many parts, the tolerance is the sum of every parts added up together, after assembly. You can't just measure the tolerance of the rotating shaft preassembly and call it a day. The burrs carrier, the grind chamber, the motor shaft, and the burrs themselves, when assembled together, will all affect the final tolerance.



The gist answer to your question is cost limitation. Low tolerance is possible with the big companies, but it is not practical/economic enough for what the costumers are willing to pay.

To your another question, in theory, you do change the burrs alignment whenever you're taking the burrs out from its carrier. There's some slop to how the burrs can sit in the carrer, if you pay close attention. But it's usually quite minor enough to be noticable. However, if a large coffee debris is stuck on the burr carrier surface, the burr will be tilted and definitely you have affected the alignment. Other than that, if the motor shaft is poorly made, or the carrier is not machined evenly, that'll be out of your hand to correct (in most cases).

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chopinhauer
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Postby chopinhauer » May 22, 2017, 1:25 am

What a great answer, Sam. You've really distilled it down to something I can now understand and appeciate.
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samuellaw178
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Postby samuellaw178 » May 22, 2017, 1:35 am

Thanks! Glad that helped! :D

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bostonbuzz
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Postby bostonbuzz » May 22, 2017, 11:47 pm

Put Mazzer burrs in their carrier and insert the bolts. Before you tighten them, feel the play.. it's enourmous. The floating burr carriers in their and all other designs add to this error.
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chopinhauer
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Postby chopinhauer » May 23, 2017, 6:17 am

bostonbuzz wrote:Put Mazzer burrs in their carrier and insert the bolts. Before you tighten them, feel the play.. it's enourmous. The floating burr carriers in their and all other designs add to this error.

I gather it's important to get rid of as much play as possible so why don't they? Sure, the answer is cost, but once people catch on that things can be done better as they currently are being done with the new SD grinders, then surely the so called 'top of the line' commercial grinders must follow suit or lose market share to a commercial grinder manufacturer who does go down this path in an economically viable way; surely, a matter of time.
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aecletec
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Postby aecletec » May 23, 2017, 6:39 am

Members here in the know as I mentioned beforehand, have reported that many manufacturers are already producing at full capacity... and they have no current interest in solving a problem that doesn't exist at the moment... it could take a lot of investment to get progressively tighter and tighter tolerances - the market that is interested in this sort of thing is hardly a blip on their radar.

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Postby boostownjoo » May 23, 2017, 7:07 am

chopinhauer wrote:I gather it's important to get rid of as much play as possible so why don't they? Sure, the answer is cost, but once people catch on that things can be done better as they currently are being done with the new SD grinders, then surely the so called 'top of the line' commercial grinders must follow suit or lose market share to a commercial grinder manufacturer who does go down this path in an economically viable way; surely, a matter of time.


I think alignment is more important on single dosing but not so critical in a normal cafe setting.
Grinder like Mazzer with floating upper burr carrier pressed down by adjustable collar are designed to be hopper fed and thus have some beans pushed down at all times. The weight of the beans pushing down would in turn load/center the burr on its own. For large busy cafe setting reliability and consistency are very important and the large Mazzers are quite good at that.