[Homeroast] Poisson's ratio WAS: Re: Compak vs Macap vs Rocky Grinders

Clay Spence clayorama at gmail.com
Tue May 18 08:00:02 CDT 2010


I think so, too, but it can be really complicated unless the deformation is
elastic, I think meaning that the object returns to its original shape when
you remove the force. Imagine stretching a bunch of loose particles (or
trying to) instead of compacting them. Poisson's ratio might be different
for the two cases. If you compact, the ratio probably depends on how much
you compact. And after you've compacted loose particles some, they usually
won't return to the original shape, and the ratio is probably different. All
that doesn't mean it can't be a useful idea for approximate reasoning.

Clay

On Tue, May 18, 2010 at 8:42 AM, Rich <rich-mail at octoxol.com> wrote:

> Casual observation in the real physical world by a disinterested observer
> tells that it does.
>
> John A C Despres wrote:
>
>> Poisson's ratio is simply about contraction or expansion when something is
>> stretched or compacted. In my mind it will work in the case of solids or
>> loose particles.
>>
>> John
>>
>> On Tue, May 18, 2010 at 7:25 AM, Kirk Janowiak <janomac at gmail.com> wrote:
>>
>>  Sorry, Mike, but Poisson applies here with ground coffee as well. Way
>>> back
>>> when I was taking agronomy coursework at Purdue, we used Poisson ratios
>>> in
>>> looking into soil compaction issues. "System" or no, Poisson ratios are
>>> discussed in any number of arrangements aggregate from sand to concrete.
>>> Doesn't have to be a solid like metal.
>>>
>>> Kirk
>>> (Janomac)
>>>
>>>
>>> On May 17, 2010, at 2:34 PM, Mike Koenig wrote:
>>>
>>>  Ray,
>>>
>>>> Please try not to abuse scientific phenomena.  Poisson's ratio has
>>>> nothing
>>>> to do with systems of particles, and applies only to solid objects,
>>>> (like
>>>> rubber or metal).
>>>>
>>>> Tamping in one axis cannot correct for clumps - you will get less dense
>>>> areas in your puck.  Applying some lateral force (I think you say you
>>>> let
>>>> the vibration of your grinder settle the puck) could take care of some
>>>> clumping (though I'm quite curious why your grinder vibrates that much,
>>>> doesn't seem right to me)...
>>>>
>>>> --mike
>>>>
>>>>
>>>> On Sat, May 15, 2010 at 2:55 AM, <raymanowen at gmail.com> wrote:
>>>>
>>>>  The Major (Silver Fireplug; BUFF) burrs do wonderful things to coffee
>>>>
>>>>> beans
>>>>> once again after 5 years' use, renewed a couple of months ago.  When I
>>>>> first
>>>>> got it, the maintenance tag said they'd been in use for 10 years- I
>>>>> presume
>>>>> at *$. There's a story in there somewhere.
>>>>>
>>>>> (Can they even access the burrs in their present push-button pop
>>>>> machines-
>>>>> and would they?) Employees in the SCAA, SCAB or SCAM union punch in,
>>>>> push
>>>>> buttons, make change, punch out and cash their check. Seems like little
>>>>> else
>>>>> was interesting to the majority in Denver town when I was seeking a
>>>>> reason
>>>>> to enjoy espresso.
>>>>>
>>>>> Why seek to enjoy espresso? As I said before, I was associated with a
>>>>> fellow
>>>>> that won the bid on an equipment lot from the SS United States in dry
>>>>> dock...
>>>>>
>>>>> "Hey, Ray- What do you know about this espresso machine?
>>>>>
>>>>> "Nuthin-' but I can count- it has 5 or 6 stations, and looks like it
>>>>> came
>>>>> from a Tijuana Cat House, with all the black and red Naugahyde and gold
>>>>> (polished Brass?) pieces...  Thus started my quest to find out how Real
>>>>> Espresso should taste.
>>>>>
>>>>> Looks like SCAA might as well be SCCA, as much as they do for the
>>>>> commercial
>>>>> cup.  Almost made "Commercial" a four-letter word, instead of "Artisan"
>>>>> the
>>>>> bean deserves.
>>>>>
>>>>> In my opinion, the Grinder is Everything.  Any real coffee shop ought
>>>>> to
>>>>> keep a stack of new burrs like the Cincinnati Kid had a stack of chips
>>>>> at
>>>>> the table in Las Vegas.
>>>>>
>>>>> Who promotes the palaver about coffee clumps surviving the packing
>>>>> tamp?
>>>>> Stand up and be counted. So coffee clumps have more structural
>>>>> integrity
>>>>> than the buildings in San Francisco in 1906, Philippines 1968, or Haiti
>>>>> more
>>>>> recently. By comparison, the raw coffee clumps out of the new burrs in
>>>>> the
>>>>> Mazzer are demolished by the Richter 10.0 vibration and tamping force
>>>>> that
>>>>> resolves to a tri-axial force by Poisson's ratio.
>>>>>
>>>>> The compression due to the axial tamping force causes transverse forces
>>>>> that
>>>>> tend to seal the puck in the filter basket. Otherwise, the brewing
>>>>> water
>>>>> would flow around the puck instead of through it, at reduced pressure
>>>>> and
>>>>> extraction and little crema formation.
>>>>>
>>>>> Conversely, a wine bottle cork screw can extract the cork when it's
>>>>> screwed
>>>>> in less than half-way. Poisson again. Screw a wood screw into the cork,
>>>>> and
>>>>> you're never pulling it out intact. P.
>>>>>
>>>>> So the grinder makes clumps. They can't survive packing and tamping- I
>>>>> have
>>>>> some extra sharp Cheddar and Irish Dubliner that might go well with
>>>>> your
>>>>> spur gear sound.
>>>>>
>>>>> Cheers, Mabuhay, Iechyd da -RayO, aka Opa!
>>>>>
>>>>> Got Grinder?
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>>> janomac at gmail.com
>>>
>>>
>>>
>>>
>>>
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