[Homeroast] Turning Bottomless Portafilter

Joseph Robertson theotherjo at gmail.com
Sat Aug 28 02:47:41 CDT 2010


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.
> _______________________________________________
> Homeroast mailing list
> Homeroast at host.sweetmariascoffee.com
>
> http://host.sweetmariascoffee.com/mailman/listinfo/homeroast_lists.sweetmariascoffee.com
> Homeroast community pictures -upload yours!) :
> http://www.sweetmariascoffee.com/gallery/main.php?g2_itemId=7820
>



-- 
Ambassador for Specialty Coffee and palate reform.


More information about the Homeroast mailing list