Bayonet + Shower Screen for DIY Espresso Machine

A haven dedicated to manual espresso machine aficionados.
Dingus

Postby Dingus » Mar 17, 2019, 3:10 pm

I'm building a direct lever espresso machine with a 44mm internal piston diameter. I'm exploring my options for portafilter + shower screen. I have noticed that commercial espresso machine bayonets have a cast-brass internal ramp to mate up with the portafilter's ramp that would be very difficult to machine. Is it possible to achieve the bayonet seal without this internal ramp?

Another possible option would be to purchase either a lower group-head bell or a bolt on bayonet. So far I have found a few of these: Astoria bell, Marzocco bayonet, and ROK bayonet. My favorite of these is the ROK bayonet due to the easy through-bolt pattern.

https://www.espressoparts.com/astoria-group-head-bell
https://www.espressoparts.com/la-marzoc ... yonet-ring
https://espressounplugged.com.au/products/bayonet-ring

So, the question is: buy or make? Are there other options for bayonets to purchase? Can I machine a simplified version of the bayonet on a lathe and mill without the internal ramp?

Thanks!

Dingus

Postby Dingus » Mar 17, 2019, 9:01 pm

Here's a teaser photo. The main thing left to figure out is the bayonet mount, screen, and lower seal.

Image

MemPast

Postby MemPast » Mar 17, 2019, 11:04 pm

Wow!

Is it open boiler--non pressurized boiler?

Dingus

Postby Dingus » Mar 18, 2019, 12:03 am

Yes! My goal is to take all of the guess work out of both temperature and pressure variables. I'm fed up with group-head offsets, warm-up times, pump fluctuations, unknown pressure, temperature decreasing during a shot, etc.

The water is heated inside the group-head.

John49

Postby John49 » Mar 18, 2019, 7:18 am

Your piston is fixed and your lever does not produce a straight up and down motion. I can't see this working.

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Bluecold

Postby Bluecold » Mar 18, 2019, 7:51 am

There's probably a slot for the lever pin to move in.

Espresso strietman machines have an external bayonet, perhaps easier to make.

Another option would be a conti lever group bell.
LMWDP #232
"Though I Fly Through the Valley of Death I Shall Fear No Evil For I am at 80,000 Feet and Climbing."

Dingus

Postby Dingus » Mar 18, 2019, 8:51 am

Bluecold wrote:There's probably a slot for the lever pin to move in.


This is correct, the fulcrum pin is inside of a slot. The Piston shaft also has a Teflon bearing to help keep it vertical. I have the movement all animated in CAD.

Espresso strietman machines have an external bayonet, perhaps easier to make.


I think you're right. This would at least make it possible to machine. You've reminded me that another option might be be to externally thread the GH and screw on a basket holder instead of a true portafilter, like the flair.

Another option would be a conti lever group bell.


This is the type of suggestion I'm looking for, thank you. Their parts look well made and available. The closest thing I could find to the bayonet in a few minutes of searching was the shower assembly. Going to need to search a little more this afternoon to find the bell. I love that the shower assembly bolts around the outside instead of with a bolt in the center.

http://www.cafeparts.com/SubCatFilter/4314/524/0:55/3
http://www.cafeparts.com/SubCat/1554/402/5

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Bluecold

Postby Bluecold » Mar 19, 2019, 2:51 am

Dingus wrote:This is the type of suggestion I'm looking for, thank you.

You're welcome:)
The Cimbali group bell has a similar construction.
LMWDP #232
"Though I Fly Through the Valley of Death I Shall Fear No Evil For I am at 80,000 Feet and Climbing."

Dingus

Postby Dingus » Mar 19, 2019, 8:55 am

I found a new key word! "coupling bell"

https://www.google.com/search?q=%22espr ... 07#imgrc=_

I found coupling bells for the Cimbali Group and Victoria Arduino groups, but they are $219 and $112 just for the bayonet.

http://www.cafeparts.com/Espresso-Machi ... M21-Junior

http://www.cafeparts.com/Espresso-Machi ... emid=16871

Maybe it's time for me to explore brass casting.

Judokus

Postby Judokus » Mar 19, 2019, 1:36 pm

Hi about going for the Bezzera bell? At least in Germany it's not too pricey.
https://www.avola-coffeesystems.de/ansatzglocke-fuer-filtertraeger-bezzera-bz10-bz07/8000009

Whenever I dismantle my BZ07 for cleaning I feel like building my own espresso forge clone based on this bell and the portafilter.

Any idea on how to get rid off the trapped air above the coffee puck? May be the easist is to stick with the rok as the water path would be shorter?