Burr "sharpness" / tooth angle / outfall

Grinders are one of the keys to exceptional espresso. Discuss them here.
jb-0101

#1: Post by jb-0101 »

Hey all,

Can anyone explain what sort of effect you would expect to see with burrs that have a "sharper" end tooth? When I say sharper, the picture probably explains it. These are side profiles of Ditting 804 burrs: The original cast burrs that were sharpened by SSP, and the new Lab Sweet burrs. As you can see, the original burrs look sharper, with pointier angles on the cutting surface, whereas the lab sweet look fuller, or rounder.

The lab sweet has had about 20kg through them, the original have had about 35kg. The lab sweet we're noticably duller to touch out of the box than the originals with about 20kg on them.

I expected the lab sweets to feel sharper!!


Eiern

#2: Post by Eiern »

I think two things will happen, it can grind a little finer (for espresso) and it will generate more fines.

This is like the difference between SSP 64mm Brew and 64mm Multi Purpose, where Brew is pure sawtooth and Multi Purpose have flat spots from having the top part shaved off.

Your first set here doesn't look pure sawtooth, it looks like it has the flat spots but a little more outfall. Both are probably as "sharp" on the edge but one has less outfall/gap. Some turkish or espresso burrs has no outfall at all, their edge is completely flat.

By the way, these teeth run opposite of what one would think, or opposite of the cutting edges at the earlier seciton, so they don't cut the beans at this final stage, they let out and shape the particles.

Eiern

#3: Post by Eiern »

Correction: I see now that the edge also look less steep in the photo. If these run opposite like I mentioned I don't think the angle there has that much effect, it's usually rounded a little with a lot of SSP burrs, and my 98mm Ultra Low Fines burrs have smooth U shaped outfall instead of sawtooth.

ira
Team HB

#4: Post by ira »

I would guess that you see the flats on burrs designed to grind smaller as they allow setting the maximum dimension of a particle that can escape smaller than if they leave the points at the edge of the burrs. Looking at those 2 I would guess that the EK burr would generate more fines as it looks like it will smash the coffee as it's exiting more than the SSP burr, but what I don't know about burr design would fill a library so I would not be surprised to completely wrong. Roller grinders and ghost burr grinders seem to have the least fines and they only smash the beans so maybe I'm completely wrong.

Marmot

#5: Post by Marmot »

This is an interesting topic!
I have two old KF804s with cast iron burrs. The one from 1986 has hardly ever been used and I suspect the burrs are in good shape although I have no visual way of telling since they are dull by design.
These burrs deliver the best taste among all my grinders and can grind very fine. I grind at about 2.6 for light roasts with long preinfusions with flow control (burrs almost touching at 1).
Some time ago I was testing grinding for turkish and the cast iron burrs could grind the finest by far.
I assume the end of the burr teeth are like a plateau instead of a sharp edge and the beans get cut in the beginning but at the end they may get squashed? I think I remember somewhere reading that the particles from the cast iron burrs appear more round than from other burr types.

jb-0101 (original poster)

#6: Post by jb-0101 (original poster) »

Eiern wrote:By the way, these teeth run opposite of what one would think, or opposite of the cutting edges at the earlier seciton, so they don't cut the beans at this final stage, they let out and shape the particles.
I have often wondered about this! I've just checked, and SSP 64mm lab sweet and the Ditting 80mm lab sweet both have finishing teeth where the sharp edge runs the same direction as the earlier cutting teeth, but SSPs 64mm brew and MP, and the 80mm (for Ditting and EG1 ultra - same burr i understand), and EK burrs run the opposite direction, so on the final edge instead of having the two sharp angled edges cross each other like scissors, the two dull angled edges cross each other. But on the earlier cutting teeth it's the sharp edges that cross each other.




Can someone explain why this is? Seems counterintuitive!!

jb-0101 (original poster)

#7: Post by jb-0101 (original poster) »

Eiern wrote:I think two things will happen, it can grind a little finer (for espresso) and it will generate more fines.
Sorry - do you mean the lab sweet will grind finer and create more fines, or the original burrs will grind finer and create more fines?