[Homeroast] Turning Bottomless Portafilter

Demian Ebert coffehound at gmail.com
Sat Aug 28 12:47:10 CDT 2010


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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>
>
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