[Homeroast] Turning Bottomless Portafilter

Rich rich-mail at octoxol.com
Sat Aug 28 13:07:29 CDT 2010


A 2" metal cutting hole saw in a drill press is capable of snatching 
something like a portafilter out of a press vice that is clamped to the 
table and flinging it a very long way at a very high velocity. 
Accidents with hand tools require stitches while accidents with  machine 
tools can require artificial limbs or morticians.  You can be learning 
the difference between a professional and amateur in nanoseconds.

Demian Ebert wrote:
> Well all I can say in response to that metal working lesson is I guess
> I'm lucky. Although a certain amount of care and planning went in to
> the exercise. Having succeeded once I'd try again and I probably
> wouldn't learn until I broke something or was bleeding.
> 
> I did see some really nice metal-specific hole saws on the Otis
> service cart the other day. They've been reworking the elevators in
> our building for months. The guy said they worked like a charm.
> Perhaps the wood model could be upgraded if I had to do it again.
> 
> Demian
> 
> Got hole saw?  :)
> 
> 
> On 8/28/10, Joseph Robertson <theotherjo at gmail.com> wrote:
>> Well RayO,
>> I did enjoy reading this one. Although if I hadn't worn a  welders hat
>> studied metallurgy in college and a worked as machinist in a former life I
>> probably would have not responded to this post. I do believe I could cut my
>> next portafilter in the time it took you to write this last post of yours.
>> In fact I'm temped to give it a try. If I do I will post the results in this
>> thread. Even from the hospital if I have to.
>> I have eaten a lot of crow and hat in my day but I think not this time.
>> JoeR
>>
>> On Fri, Aug 27, 2010 at 11:58 PM, <raymanowen at gmail.com> wrote:
>>
>>>   1. "...use a hand drill / Vise to hold it and a hole saw to cut mine
>>>   out.
>>>   2. From now on I will do my own.
>>>                             [When you see something done by someone
>>>   experienced in doing it, the process always looks easy. Something looks
>>>   simple like changing the engine or automatic transmission oil and filter
>>>   when someone else does it-  or a flat tire? Looks easy when you see it
>>> done.
>>>    Show of hands- How many people actually do their own maintenance on a
>>>   regular basis?]
>>>   3. The chrome coating is real thin. the core is bronze I think. [Bronze-
>>>   like the Temple bells in Thailand? Stupid Marketing always says "Heavy
>>>   brass" or "Marine grade brass"] Their specific heat is lower than that
>>> of
>>>   the water they don't touch...
>>>   4. Very easy to cut with a hole saw."
>>>
>>> Maybe Not-
>>> Did you see the machinist using a Hole Saw or claw hammer?  He did Not.
>>> In order to do the machine work with precision, conserve tools and the
>>> porta
>>> filter handle itself, the cutting tools and workpiece were firmly mounted
>>> on
>>> the lathe.
>>>
>>> If your friend did not fracture the porta filter handle between the two
>>> jaws
>>> of the bench vise; did not break the pilot hole drill bit when the hole
>>> saw seized in the work piece, crack his wrist, yank the pf out of the vise
>>> as it broke and busted the drill motor when it hit the floor, he's either
>>> a
>>> Magician or extremely lucky.
>>>
>>> Luck and Magic may be entertaining, but have no place in a machine shop or
>>> on the highway. (When you feel inclined to buzz it over 100, are all the
>>> lug
>>> nuts torqued, tire pressures and engine oil just right? Do you Know so or
>>> just Hope so?)
>>>
>>> Cutting out the entire bottom of a portafilter might seem easy with a
>>> large
>>> hole saw, bench vise and hand drill, but it's not the all-pro move. It
>>> will
>>> probably cost you some painful surgery, a hole saw, a hand drill, a porta
>>> filter and some CSA points.
>>>
>>> At Colo School of Mines Earth Mechanics Research Institute, I used a
>>> 500-ton
>>> press and 12,000 psi triaxial pressure to test and chart record the
>>> failure
>>> point of 2" OD X 4"L oil shale cores, up to 480° C, (Love PID controller,
>>> type K s/s sheathed grounded junction thermocouples) and my strain gage
>>> load
>>> cell.
>>>
>>> According to an ME/ Chem E friend, "Some of the stronger bronzes need full
>>> hydrodynamic (pressure) lubrication, or they gall and seize. (That's what
>>> grabs and breaks the hole saw, your wrist, and yanks the pf out of the
>>> vise
>>> if you had a good grip on the drill)
>>>
>>> The heavily leaded bronzes survive much better when lubrication is
>>> marginal,
>>> if speeds are Slow Enough. Ever seen a slow hand drill? Hammer Mechanics
>>> usually run full-speed.
>>>
>>> The opposing material and finish can make a big difference in the wear
>>> rate
>>> and tendency to seize and gall. (Break your wrist)
>>>
>>> Poor geometry usually can not be compensated for with "better" as-cast or
>>> annealed materials." The tabs of 58mm pf handles each have to withstand
>>> almost 300 pounds in shear at 9 bar pressure. Things could go rong in a
>>> hurry if the shot stalls and the OPV doesn't bypass and relieve the pump
>>> pressure, like my former Crapesso.
>>>
>>> Don't even think of using type J thermocouples around moisture- the couple
>>> is Iron/ Constantan. Guess which one corrodes like Hell and destroys the
>>> junction?  Type K couple is Chrome-Nickel/ Aluminum-Nickel or Chromel/
>>> Alumel.(Was © Omega) The Chromel is a laboratory-grade Nichrome- the
>>> heater
>>> wire in toasters- and can withstand ≤ 3000° F.  Alumel is a little lower
>>> and
>>> type K is a stable Seebeck couple at 2700° F.
>>>
>>> Cheers, Mabuhay -RayO, aka Opa!
>>>
>>> Do what you always did, get what you always got- If you get back without
>>> an
>>> ambulance ride or tow truck, maintenance was OK.
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>>
>>
>> --
>> Ambassador for Specialty Coffee and palate reform.
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