Spinning for distribution?

Beginner and pro baristas share tips and tricks.
The_Mighty_Bean

#1: Post by The_Mighty_Bean »

I posted this idea over on CG, and there was a bit of debate there. In reading some of the HB threads about using a dental vibrator (or taking a quick trip to the sex toy shop), I was reminded of this intuition I had.

My goal is a practical, inexpensive way to improve distribution at home. I was thinking that centrifugal force might help. What about rigging something like a salad spinner to hold the basket- you'd dose into the basket, pop it into a mounting device, maybe you'd need to "cap" it somehow to keep grounds from flying out initially.

Thoughts?


~tMb

Celebrian

#2: Post by Celebrian »

wouldn't that distribute the grounds around the outside of the basket? you'd have a less dense spot in the middle.
Then again, maybe I don't know what I'm talking about, and it could be good.
-Alex

The_Mighty_Bean

#3: Post by The_Mighty_Bean » replying to Celebrian »


This is where I need a little help with the physics.. I know centrifugal force would pull the grinds inward making it dense in the middle.And I think centripetal force pushes outward like you were talking about, and like in those carnival rides where you are on the spinning wheel.

I don't know if there's a way to balance those forces to even the distribution?


[bad physics edited out after others corrected me, thanks guys.]

If you look at the way the Versalab M3 throws the grounds, there's a bit of a dimple in the center... I think this might be similar, and you simply do a swipe or dose in a tad of extra coffee to fill it in. The density wouldn't quite be identical to the spun grounds, but possibly a lot closer than you could ever get with WDT.

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gadflea

#4: Post by gadflea »

Celebrian is right. The grounds would go to the outer walls of the basket leaving a hole in the center.
There is no such thing as a centrifugal force. Centripetal force is that force causing a body to accelerate (change direction) in a circular motion. It is directed inwards, from the body being spun towards the center of the circular path being traveled. If you are spinning a yo yo around over your head, the string is the centripetal force that keeps the yo yo from flying off into your bay window.
The centripetal force in your thought experiment would come from the walls of the basket pushing against the grinds so that they do not fly out horizontally (in a perpendicular path to be specific). The force provided by the walls cannot push the grinds to the center, it can only prevent them from escaping. therefore the grinds would collect on the walls leaving a hole in the center of the basket.
You can google centripetal force to get some diagrams illustrating my explanation above. It is kind of hard for me to explain it without drawing pictures.
Hope this helps.

Celebrian

#5: Post by Celebrian »

actually, there is such a thing as centrifugal force, in fact, that's what distributes the grounds around the outside of the basket. It's long and complicated, and i'm gonna simplify things waaay too much for comfort, but hopefully, it will make things a lot easier.
really dodgey diagram below:
Image

So....the centripetal force is the force required to move the object around a circular path at a constant speed. the force is a vector (meaning it has both a magnitude and direction), which points inward at the centre of the circular path. Centrifugal force is the force directed outwards on the object, which is of equal magnitude to the centripetal force exerted on the object. But the centrifugal force isn't....real as such. i mean, it feels real, but it's all relative.

Let's say that you're in a car and it takes a sharp bend...the passengers may feel like they are thrown to one side of the car, when in reality, there is no force acting on the passengers, but reacting to the acceleration of the car....(blah blah...relativity...blah...physics).


SO.
for the simplicity of explaining stuff, we're gonna assume that centrifugal force is just the force pushing the object away from the circle centre.

Centripetal = going in
Centrifugal = out

How does this relate to coffee?

Well. Spinning the basket would cause the grounds to travel in this circular path, and both centripetal and centrifugal forces would act on them. centripetal forces is what keeps the grounds in the basket, traveling in a nice circle. the centrifugal force would push them out to the sides of the basket, therefore creating a less dense spot in the middle.

Now all of you clever baristas can explain the results. Chances are you already know what's gonna happen. :)
-Alex

The_Mighty_Bean

#6: Post by The_Mighty_Bean »

Celebrian wrote:actually, there is such a thing as centrifugal force, in fact, that's what distributes the grounds around the outside of the basket....



Now all of you clever baristas can explain the results. Chances are you already know what's gonna happen. :)


Thank you so much for bringing back my nightmares from the physics class in college where the class average was in the 40s. An important part of why I switched from pre-med to pre-law. ;)


But I am picturing this spun basket with the grounds forced to the outside. I think it would take a heck of a spin to force a "ring" shape with a hole in the middle, which would be terrible distribution.

But perhaps a gentler spin might result in the most even convex tamp we've ever seen, complete with a nice side seal? As I said in my first post, maybe one could artificially help it out by slightly packing the middle, post-spin. No idea if that would be necessary.

I dunno, that's just intuition, could be way off.

~tMb

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RogerB

#7: Post by RogerB »

Celebrian wrote:actually, there is such a thing as centrifugal force, in fact, that's what distributes the grounds around the outside of the basket. It's long and complicated, and i'm gonna simplify things waaay too much for comfort, but hopefully, it will make things a lot easier...
Centrifugal force is indeed a fiction. Centripetal (from the latin, "center seeking") forces are "balanced" by acceleration, and the illusion of centifugal force is due to the tendency of any object travelling in a straight line to continue travelling in a straight line unless acted upon by an outside force (Newton's Third Law).

Centrifugal (from the latin, "center fleeing") force, if real, would portend that the yo-yo you're swinging around your head, once released, would travel away from the circle's center radially, when in fact it departs tangentially; that is, perpendicular to the radius of the circular path it was travelling only a moment before.

As for spinning the filter basket...

...I think we're overthinking it.

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Psyd

#8: Post by Psyd »

RogerB wrote:Centrifugal force is indeed a fiction.
So is Ishmael's white whale, but I bet we all know his name. Centrifugal force is the name we give to the combination of physical circumstances that keep you alive on the spinny carnival ride.
In any case, if you were to put the entire basket on the inside of a spinning thing, with the opening of the basket facing the center of the rotation, would it distribute any better or simply be a very complicated method of 'thumping'?
Espresso Sniper
One Shot, One Kill

LMWDP #175

The_Mighty_Bean

#9: Post by The_Mighty_Bean »

RogerB wrote:
As for spinning the filter basket...

...I think we're overthinking it.
Not if it could be done simply and quickly. If it worked better and was faster than the WDT I'd do it in a heartbeat.
Psyd wrote:would it distribute any better or simply be a very complicated method of 'thumping'?
Well that is the question. There's been lots of discussion of thumping, and I think the gist of it, at least lately, is that you tend to get an uneven pack with more density towards the bottom. That's why people are talking about just uniformly agitating all the grounds sort of gently with a dental vibrator.


Now we just need a vibrator that spins.

Oh, dear.


~the Mighty innuendo

KillerQ

#10: Post by KillerQ »

Hey all,

Cool concepts, but for now, I'll stick with sifting through the grounds with a straightened paperclip to ensure there are no clumps or pockets, then a quick shake/tap to make sure it's level before tamping (call this procedure what you will).... According to my naked PF, this works pretty well!

Later,

Matt!