Knob Coffee Grinder (Kickstarter)

#1: Post by **Steveko23** » August 26th, 2021, 9:58 pm

Anyone know anything about this?
https://www.knobgrinder.com/

Seems interesting, though I'm not sure the details of the burrs...

#2: Post by **bakafish** » August 26th, 2021, 10:17 pm

Interesting, but if this is the burr set, shouldn't the outer burr turn counterclockwise?

#3: Post by **myso** » August 27th, 2021, 12:57 am

Inner burr is stationary and the ring burr rotates. (Similar to etzmax)

#4: Post by **neury** » August 27th, 2021, 5:02 am

Hi,
I think it is web browser fault. The arrow is not showing the rotation. It is showing the place of axle which is absent.

#5: Post by **bakafish** » August 27th, 2021, 12:17 pm

neury wrote: Hi,
I think it is web browser fault. The arrow is not showing the rotation. It is showing the axle place which is absent.

Oh! I see the correct picture when I maximize the browser window.
But you can see the animation on the website like below which shows the outer burr rotates clockwise.
Sorry, I can only capture the static picture.

　
This video shows it rotates clockwise at 1:04, but counterclockwise at 1:08.

　
0:27 counterclockwise, but 0:30 clockwise.

　
I think this grinder is not finished yet. They may want it rotates clockwise, but it needs a custom inner or outer burr and the burr manufacturer may ask them to order at least hundreds of burr set. So they can only use the normal burr set now and show you the concept.
　
　

#6: Post by **TenLayers** » August 27th, 2021, 12:25 pm

Engineering is coming out of Turkey. Wonder if grinds to Turkish coffee levels

Edit, Oh, I see on the video they say from a Turkish grind on up.

#7: Post by **Pressino** » August 27th, 2021, 2:19 pm

They mention that their design eliminates the problem of wobbling of the axle, which they describe as a significant problem in other grinders. They solve this problem by eliminating the axle, which I guess they do by having two nested cylinders, one of which holds the bottom burr and the other the top. I'm just guessing, since they really don't describe the mechanism in detail. Maybe they use a morse type taper to ensure concentricity over time with wear.

It's an interesting idea, but I think the problem has already been solved in well-engineered grinders that employ axles...they use a set of at least two sealed ball bearings seated in solidly made metal frames. The concentric nested cylinder idea seems to be particularly nice for grind adjustment, a definite improvement in that regard. My main concern would be wear on the rotating cylinders...that would depend on how they are constructed. Are bearings of some sort used and is there a provision to take up slack during wear?

#8: Post by **neury** » August 27th, 2021, 3:01 pm

bakafish wrote:Oh! I see the correct picture when I maximize the browser window.
But you can see the animation on the website like below which shows the outer burr rotates clockwise.
Sorry, I can only capture the static picture.
image
　
This video shows it rotates clockwise at 1:04, but counterclockwise at 1:08.
video
　
0:27 counterclockwise, but 0:30 clockwise.
video
　
I think this grinder is not finished yet. They may want it rotates clockwise, but it needs a custom inner or outer burr and the burr manufacturer may ask them to order at least hundreds of burr set. So they can only use the normal burr set now and show you the concept.
　
　

Yep! You got the point. The prototype made for Kickstarter video is turning CCW, but grinder will be turning CW as usual in serial production. It is all about the production quantity as you said. Kickstarter campaign will provide that necessary quantity. You are very careful by the way.

#9: Post by **domo** » August 27th, 2021, 4:01 pm

Pressino wrote:They mention that their design eliminates the problem of wobbling of the axle, which they describe as a significant problem in other grinders.

Etzinger is also working on a manual grinder without axles. It's called etz-I and will ready to buy this fall. They posted some pics on Instagram.

#10: Post by **neury** » August 27th, 2021, 8:46 pm

Pressino wrote:They mention that their design eliminates the problem of wobbling of the axle, which they describe as a significant problem in other grinders. They solve this problem by eliminating the axle, which I guess they do by having two nested cylinders, one of which holds the bottom burr and the other the top. I'm just guessing, since they really don't describe the mechanism in detail. Maybe they use a morse type taper to ensure concentricity over time with wear.

It's an interesting idea, but I think the problem has already been solved in well-engineered grinders that employ axles...they use a set of at least two sealed ball bearings seated in solidly made metal frames. The concentric nested cylinder idea seems to be particularly nice for grind adjustment, a definite improvement in that regard. My main concern would be wear on the rotating cylinders...that would depend on how they are constructed. Are bearings of some sort used and is there a provision to take up slack during wear?

Hi, there are bearings between those cylinders. They are not touching each other directly. Concentric cylinders also maintain more space for coffee and ease of cleaning. Also, the biggest advantage is wobbling no more happens, because the bearing is located around the outer burr. Bearings of standard grinders with axle cannot be located inside the burr where the grinding happens.