Baratza Sette 270 vs Kinu M47 - Page 2

#11: Post by **renatoa** » September 1st, 2017, 4:14 pm

The movement between the inner/outer burr walls is what we call grinding process, and this movement linear speed is given by RPM only, being the same whatever burr is rotating.
Probably the confusion comes from the upper input area, where walls have indeed significantly different diameters, but that area is only a bean breaker, the real grinding is done in the lower part, where walls are parallel and almost touching.

#12: Post by **ira** » September 1st, 2017, 4:22 pm

another_jim wrote:Actually, it roughly triples the grind speed expected from conical burrs that size; the rotation of the outer burrs augurs the beans into the burrs far more effectively.

While i also saw that in the marketing package, I have to believe it's just marketing. How could which burr turns affect how they grind. It makes no sense that the beans would care.

Ira

September 1st, 2017, 4:37 pm

The outer burr vs inner burr turning did sound like marketing when I first read about it. But it does make sense. The linear velocity of the burr is a product of angular velocity(or rpm) multiplied by radius. When you turn the outer burr instead, you can expect the actual shear to be slightly higher due to higher radius.

For a 38mm burr, the inner cone burr measures from *roughly* 25mm (top cone) to 38mm (bottom cone). Outer burr spans around 36mm-40mm+ (top to bottom). Just a few mm but it contributes. Of course the redesign of the outer burr plays a major role as well. You can't just turn the outer burr alone and expect the same magnitude of improvement.

p/s: Just realize the off-the-head numbers are obviously wrong. I will add exact measurement when I get to my Helor grinder.

#14: Post by **Tolis85** » September 1st, 2017, 7:03 pm

Well, Einstein says that speed is always relative to an observer(bean). So from the beans point of view its the same whichever burr rotates. BUT, if either rotates at half the speed of light or more we would have a significant Lorentz factor that would make the burr seem larger since space would expand. I'm not sure how many fines that would produce though

September 1st, 2017, 7:13 pm

ira wrote:While i also saw that in the marketing package, I have to believe it's just marketing. How could which burr turns affect how they grind. It makes no sense that the beans would care.

Ira

Um, I reviewed this grinder. Obviously something you haven't

September 1st, 2017, 8:25 pm

Well, unless you reviewed this grinder and a different one with the same burrs and the inside turning, I'd suggest it's all speculation.

Ira

September 1st, 2017, 10:38 pm

No, Ira I didn't test it against multiple redesigns of the same grinder, nor against other denizens of the what if universe. In the real world, it grinds a double shot in about six seconds, roughly the same speed as a Mazzer Major. This is three times as fast as almost anything with similar sized burrs. The reason is that grind speed depends mostly on how fast the beans feed thorough the burrs. With the outer burr rotating, the "suction" effect on the beans is far greater than when the inner burr rotates. In effect, the design makes the burrs its own augur. The auguring effect also means the grinder does not slow down for single dosing.

Grind speeds this fast are associated with relatively massive grinders; I'm guessing that maybe some of the initial reliability problems are associated with the unexpected stresses of souping up a small grinder to this level of performance.

In terms of adjustability and taste; the Sette is very easy to set for the desired flow and dose; but the resulting taste is not all that tunable, it stays highly extracted and forgiving pretty much regardless of the grind setting. I do not know how the Kinu works in these respects.

#18: Post by **ira** » September 1st, 2017, 11:45 pm

I accept it's a fast grinder, that's a given, what I can't accept without some explanation or proof is why you think turning the outside burr has any effect on grind speed. How does any bean in the column of beans know which burr is turning and if it can't tell, why does it matter which one turns?

For a simple test, let's mount the Sette on a rotary table located with the burr centerline exactly aligned with the table centerline. Then let's set up that table so that it spins at the exact same speed as the outer burr so that when we look down when the grinder is running, the outer burr appears stationary. Do you think the grinder will suddenly grind slower?

Ira

September 2nd, 2017, 1:27 am

Think of the inner and outer burrs as inner and outer parts of the same circle. To do one rotation, a point near the centre of the circle (in our case this can be seen as the inner burr) travels a much smaller distance than a point further out (the outer burr). Both parts must do a single rotation in the same amount of time if moving at the same number number of revolutions per minute, therefore the point further from the centre (the outer burr) must have a higher speed. Obviously with burrs one of them is fixed, but for the purposes of explaining the physics this is how my brain is best able to describe it - you can tell I'm not a physicist!

As to why this produces a better cup than just turning the inner burr at a higher speed I can't answer...

#20: Post by **renatoa** » September 2nd, 2017, 2:21 am

Your explanation above would make a sense if the circle has a significant weight, as is the case of the beans input.
But the exit circles are almost equal, probably 1mm difference at 40mm diameter, far from the triple claim...
The increased output of Sette can be rather explained by the burrs cut than anything else.
For example the output difference between Feldgrind and Kinu M38 is almost double, like in 30 vs 48 seconds, to grind same beans, turned at same (electric) RPM. But the Kinu M38 requires 40 Nm force compared to 18Nm force required by Feldgrind

can anyone explain this difference other than burrs shape ?