Is there a standard catalog of rectangular cross-section O-rings?
It's a hot-water application, in fact the group gasket for an old
espresso machine.

The dimensions need to be about 2 1/4" OD, 1 7/8" ID but a little
over 1/4" thick, say 5/16". The thickness is the sticking point.
Long ago I machined a teflon ring for the job, but to my supreme regret
I damaged it on removal and the only remaining stock on hand is .250"
thick. That's not quite enough.

McMaster sells 3/8" sheets, but the smallest piece is six by six inches,
$60 and lots of work. To my surprise there's nothing on Amazon. Tap does
not list teflon at all. Back in the day I just went to Abe Schuster Plastics
in Oakland CA and bought a bit of scrap 8-)

It's possible a round-section Buna O-ring could be crammed into the groove
but it looks like Parker does not make one that comes close (too skinny)
and the curved cross section will promote un-centering of the gland.

Another option is to use the too-thin teflon and put a slim backing
o-ring under it, Parker 2-034 or 2-137.

Writing this helped collect my thoughts, if you have anything to add
please do.

Thanks for reading!

bob prohaska

On Mon, 24 Apr 2023 15:51:41 -0000 (UTC)
bob prohaska <bp@www.zefox.net> wrote:

<snip>
>Is there a standard catalog of rectangular cross-section O-rings?
>It's a hot-water application, in fact the group gasket for an old
>espresso machine.

Probably already checked but...

Any chance this Expresso parts place has something close enough?

https://www.espressoparts.com/collections/browse-common-espresso-machine-parts-group-gaskets

--
Leon Fisk
Grand Rapids MI

On Mon, 24 Apr 2023 15:51:41 -0000 (UTC), bob prohaska
<bp@www.zefox.net> wrote:

>Is there a standard catalog of rectangular cross-section O-rings?
>It's a hot-water application, in fact the group gasket for an old
>espresso machine.
>
>The dimensions need to be about 2 1/4" OD, 1 7/8" ID but a little
>over 1/4" thick, say 5/16". The thickness is the sticking point.
>
>Long ago I machined a teflon ring for the job, but to my supreme regret
>I damaged it on removal and the only remaining stock on hand is .250"
>thick. That's not quite enough.
>
>McMaster sells 3/8" sheets, but the smallest piece is six by six inches,
>$60 and lots of work. To my surprise there's nothing on Amazon. Tap does
>not list teflon at all. Back in the day I just went to Abe Schuster Plastics
>in Oakland CA and bought a bit of scrap 8-)
>
>It's possible a round-section Buna O-ring could be crammed into the groove
>but it looks like Parker does not make one that comes close (too skinny)
>and the curved cross section will promote un-centering of the gland.
>
>Another option is to use the too-thin teflon and put a slim backing
>o-ring under it, Parker 2-034 or 2-137.
>
>Writing this helped collect my thoughts, if you have anything to add
>please do.

The dimensions may well be metric.

Would a Parker X-Ring Seal work?

..<https://www.parker.com/literature/O-Ring%20Division%20Literature/Bulletin%20pdf's/xring.pdf>

Joe Gwinn

"bob prohaska" wrote in message news:u268id$db84$1@dont-email.me...

Is there a standard catalog of rectangular cross-section O-rings?
It's a hot-water application, in fact the group gasket for an old
espresso machine.

The dimensions need to be about 2 1/4" OD, 1 7/8" ID but a little
over 1/4" thick, say 5/16". The thickness is the sticking point.

------------------

Disk brake calipers have similar seals, though selecting them by size
instead of vehicle might be difficult.

When I couldn't find the exact OD, ID and length for a hydraulic cylinder
seal I machined a spacer to adapt the closest match.

"bob prohaska" wrote in message news:u268id$db84$1@dont-email.me...

Is there a standard catalog of rectangular cross-section O-rings?

-------------------------

How about two cup seals?

Place the flats against the groove walls, not each other back-to-back, so
the loaded one doesn't crush the other.

Leon Fisk <lfiskgr@gmail.invalid> wrote:
> On Mon, 24 Apr 2023 15:51:41 -0000 (UTC)
> bob prohaska <bp@www.zefox.net> wrote:
>
> <snip>
>>Is there a standard catalog of rectangular cross-section O-rings?
>>It's a hot-water application, in fact the group gasket for an old
>>espresso machine.
>
> Probably already checked but...
>
No, I didn't know about that one. Good find, and bookmarked.

> Any chance this Expresso parts place has something close enough?
>
> https://www.espressoparts.com/collections/browse-common-espresso-machine-parts-group-gaskets
>
Nothing by manufacturer (Olympia) and nothing obvious by nominal
size (49 mm). That doesn't mean they don't have what I need, but
it'll take some digging.

It's a good web site, thanks for making me aware of it!

bob prohaska

Joe Gwinn <joegwinn@comcast.net> wrote:
> On Mon, 24 Apr 2023 15:51:41 -0000 (UTC), bob prohaska
> <bp@www.zefox.net> wrote:
>
>>Is there a standard catalog of rectangular cross-section O-rings?
>>It's a hot-water application, in fact the group gasket for an old
>>espresso machine.
>>
>>The dimensions need to be about 2 1/4" OD, 1 7/8" ID but a little
>>over 1/4" thick, say 5/16". The thickness is the sticking point.
>>
>
> The dimensions may well be metric.
>
If so, they're very oddly chosen. 58.2 mm OD, 47.5 mm ID, thickness
is a bit vague but 7-8 mm seems to be the range.

> Would a Parker X-Ring Seal work?
>
> .<https://www.parker.com/literature/O-Ring%20Division%20Literature/Bulletin%20pdf's/xring.pdf>
>

Not in a straightforward way, if I'm understanding the sizing pattern
correctly. The trouble is the thickness needed, too big for the OD.

For the moment I've stuffed a 2-034 o-ring under the (too thin) Teflon
flat gasket I have now. That shimmed it up enough to let me make coffee.

Thus fortified, I'll explore further!

Thanks for writing,

bob prohaska

>

Jim Wilkins <muratlanne@gmail.com> wrote:
> "bob prohaska" wrote in message news:u268id$db84$1@dont-email.me...
>
> Is there a standard catalog of rectangular cross-section O-rings?
> It's a hot-water application, in fact the group gasket for an old
> espresso machine.
>
> The dimensions need to be about 2 1/4" OD, 1 7/8" ID but a little
> over 1/4" thick, say 5/16". The thickness is the sticking point.
>
> ------------------
>
> Disk brake calipers have similar seals, though selecting them by size
> instead of vehicle might be difficult.

I didn't think of brake parts. The seals won't be food-grade, but anything
that can withstand hot brake fluid is likely to be pretty inert 8-)

It turns out O'Reilly's Auto lists replacement pistons by OD,
the sizes step from 57.7 to 59.2 mm. If the photo is any guide,
the seals are much too skinny, but it might be worth a visit.

>
> When I couldn't find the exact OD, ID and length for a hydraulic cylinder
> seal I machined a spacer to adapt the closest match.

That's sort of where I am now. I use the Teflon for structure and add an
o-ring groove on the rear face in order to obtain the overall thickness.

Thanks for writing!

bob prohaska

On Mon, 24 Apr 2023 20:21:44 -0000 (UTC), bob prohaska
<bp@www.zefox.net> wrote:

>Jim Wilkins <muratlanne@gmail.com> wrote:
>> "bob prohaska" wrote in message news:u268id$db84$1@dont-email.me...
>>
>> Is there a standard catalog of rectangular cross-section O-rings?
>> It's a hot-water application, in fact the group gasket for an old
>> espresso machine.
>>
>> The dimensions need to be about 2 1/4" OD, 1 7/8" ID but a little
>> over 1/4" thick, say 5/16". The thickness is the sticking point.
>>
>> ------------------
>>
>> Disk brake calipers have similar seals, though selecting them by size
>> instead of vehicle might be difficult.
>
>I didn't think of brake parts. The seals won't be food-grade, but anything
>that can withstand hot brake fluid is likely to be pretty inert 8-)
>
>It turns out O'Reilly's Auto lists replacement pistons by OD,
>the sizes step from 57.7 to 59.2 mm. If the photo is any guide,
>the seals are much too skinny, but it might be worth a visit.
>
>>
>> When I couldn't find the exact OD, ID and length for a hydraulic cylinder
>> seal I machined a spacer to adapt the closest match.
>
>That's sort of where I am now. I use the Teflon for structure and add an
>o-ring groove on the rear face in order to obtain the overall thickness.

Why not just machine the whole seal from solid Teflon, starting with
solid Teflon? It may be the cheapest way, unless one can find the
expresso maker.

Joe Gwinn

Joe Gwinn <joegwinn@comcast.net> wrote:
> On Mon, 24 Apr 2023 20:21:44 -0000 (UTC), bob prohaska
> <bp@www.zefox.net> wrote:
>
>>Jim Wilkins <muratlanne@gmail.com> wrote:
>>> "bob prohaska" wrote in message news:u268id$db84$1@dont-email.me...
>>>
>>> Is there a standard catalog of rectangular cross-section O-rings?
>>> It's a hot-water application, in fact the group gasket for an old
>>> espresso machine.
>>>
>>> The dimensions need to be about 2 1/4" OD, 1 7/8" ID but a little
>>> over 1/4" thick, say 5/16". The thickness is the sticking point.
>>>
>>> ------------------
>>>
>>> Disk brake calipers have similar seals, though selecting them by size
>>> instead of vehicle might be difficult.
>>
>>I didn't think of brake parts. The seals won't be food-grade, but anything
>>that can withstand hot brake fluid is likely to be pretty inert 8-)
>>
>>It turns out O'Reilly's Auto lists replacement pistons by OD,
>>the sizes step from 57.7 to 59.2 mm. If the photo is any guide,
>>the seals are much too skinny, but it might be worth a visit.
>>
>>>
>>> When I couldn't find the exact OD, ID and length for a hydraulic cylinder
>>> seal I machined a spacer to adapt the closest match.
>>
>>That's sort of where I am now. I use the Teflon for structure and add an
>>o-ring groove on the rear face in order to obtain the overall thickness.
>
> Why not just machine the whole seal from solid Teflon, starting with
> solid Teflon? It may be the cheapest way, unless one can find the
> expresso maker.

That's roughly how I got to where I am now. I could do it again, but
was just hoping for something easier and less expensive. Looks like
it'll be easier _or_ less expensive. Teflon is too soft to chuck, so
at least one and maybe two mandrels will be required. Memory has gone
rather hazy, the gasket I carelessly damaged lasted more than twenty
years. Only then did I discover that the "spare" and the stock I saved
were too thin.

What really surprised me was the cost and limited selection of
Teflon stock. No more scrap dealers, I guess.

Thanks for writing!

bob prohaska