You are perhaps right on the account of needing a coffee particle size range from 200 to 1000 microns to go from espresso to brew.renatoa wrote:Ok, I see they go forward with this ludicrous claim and goal, so it's time to demolish these false claims.
Beware, the following are not guesses, but simple math and logic.
If this 3 microns per click would be true, then this means that the whole range of particle size able to be dialed will be 3 * 180 = 540 microns.
This is simply not enough for a grinder to be capable to switch from espresso to brew. You need at least 800 microns range, from 200 to 1000, for this goal.
This is the first fact.
Where you are wrong, however, is in assuming that the burr spacing translates directly to the particle size.
It doesn't, and you can check that by measuring the burr spacing and the resulting grinds size distribution.
Furthermore, the relation is not only not direct 1:1, but it is also not linear: +3 microns of burr spacing doesn't always mean +3n microns of resulting particles. The differences in grind size get bigger, as the spacing gets bigger.
It very much depends on beans flexibility - that's why different coffees, even same roast batch stored differently - can grind visibly differently on the same grinder, same settings.
However - before you say 'AHA! So this 3 micron resolution bullsh** is worthless, exactly as I said!" - it is obvious, that the more incremental steps in burr spacing, the more incremental changes to the resulting grind size, even if this relation is not direct nor linear. Thus giving you more precise dial-in opportunities.
You mention that 3 micron increment is comparable with the bearing play, thus meaningless. But it isn't. The bearing play is a 'constant variable' factor - it is mostly same in any grind setting, its +/- influence on actual burr spacing linearly increasing with the vertical burr spacing, as the distance of the inner burr from the lower bearing increases. That's another reason why grind distribution tends to be tighter with finer grind settings than with coarser ones, an effect very visible with cheaper, more wobbly grinders.
So from one grind setting to the very next, the bearing play's +/- influence on burr spacing remains almost exactly the same, making the difference between average minimal burr spacing 3 microns still.
Peter himself stated, that the 80 degrees slope applies to the lowest few mm of the burr - the so-called calibration band. This is the part of the burr which defines the narrowest gap, and this part is relevant for measuring burr spacing changes as the burrs move vertically and making any kind of resolution comparisons of different burrsets/grinders.renatoa wrote:Now the second, that demonstrate the 6 microns claim wasn't true, thus even more the 3 microns claim.
Measured the burr cone and it's slope is 73 degrees at base, so 17 degrees ar top.
A last note, the burrs required for a 3/6 microns particle resolution should have, according to basic geometry, 80 degrees slope:
sin (10 deg) = 0.17 = 1mm / 30 clicks / 6 microns
So almost cylindrical. Definitely not a typical Italmill burr !