gummybun Senior Member Joined: 15 May 2008 Posts: 21 Location: canada Expertise: I like coffee
Posted Fri Jun 13, 2008, 8:16am Subject: Re: CMC Machine Lever Hybrid (renamed post)
Sorry for anyone bouncing back and over from HB - I suppose forum ettiquite would suggest that I end one? or what?... Im getting good recommendations - Thank you all.
So as for waterjet I would be concerned with the micro-ridging along the cut edge. I suppose I might consider the liquid nitrogen process to abrase it off but I think I will not (: 0
I will produce an accurate dwg. of the piston on the weekend and post it. I must say that I prefer the back to back arrangement more than the 'O' ring suggestion. The reason in my mind is as follows... 1 - 'O' rings existed in 1978 and if the builders thought they would be good enough - surely they would have used them rather that these expensive 'V' cup gaskets. 2 - In my mind, the 'O' ring will a) tend to want to roll in pressure with lateral force applied (they would seem to operate best in compression - not shear load) and b) the circular curved surface will decrease its 'blocking efficiency' under load. 3 - Conversely the 'V' gasket resists 'roll' by its' geometry and under load its 'flap' edge geometry will be forced outwards - toward the cylinder face - thereby increasing its' 'blocking' efficiency.
However the hight to width ratio of two 1/8" wide 'V' gaskets does not instill me with confidence. I would like to chemically bond the two together or consider re-milling the piston head to receive two wider gaskets.
What is NSF adhesive?
I am fortunate that this machine is easy to pull apart as there in no crazy strong springs to counter-act when re-inserting the piston. One thing at least!
orphanespresso Senior Member Joined: 19 Feb 2008 Posts: 67 Location: Troy Expertise: Professional
Espresso: Cremina Faemina Microcimbali... Grinder: Hand Grinders
Posted Sat Jun 14, 2008, 12:57am Subject: Re: CMC Machine Lever Hybrid (renamed post)
Simon
I tend to agree with you that the original seal system should be duplicated as best as possible. It is my theory that in the 'early days' a piston was machined to fit whatever seals were available, or the other way around, with parts coming from various other applications...whatever worked was fine. But by the 70's as you point out there was more engineering for precise function.
Each time I have an idea about how to work around the double lip seal I place a new order for some samples and then have to wait for a week or more to get them, so I can't report on the substitution of two seals placed back to back for the one double seal as of yet, but in a week or so I may be closer to some actual on hands results. Bonding the two seals together should be easy enough with adhesive. NSF is means food safe, which is a big issue with some folks, even though not much water will get in to the adhesive but it is best to be NSF if such an approach is possible. My grandma always said that "you've gotta eat a peck of dirt before you die" but dirt and chemicals are two different matters.
O-rings are used on the piston in the La Cimbali Micro, La Peppina, Faema Faemina, Conti Comocafe and some Caravels, 4 spring levers and a manual, and if you have ever choked a Caravel, almost standing on the lever with no bleedby of pressure past the rings (and darn thin ones as well), you develop an appreciation for the sealing capactity of the lowly O-ring.
I don't know what you do with the liquid nitrogen, but I think I need some just for the mad scientist effect
gummybun Senior Member Joined: 15 May 2008 Posts: 21 Location: canada Expertise: I like coffee
Posted Sun Jun 15, 2008, 1:07pm Subject: Re: CMC Machine Lever Hybrid (renamed post)
Here is the drawing of my CMC's piston. I posted it over at HB as well.
So with this I will assemble some existing gaskets and 'O' rings and see if any combination works for me. Now I am looking for Part numbers - or - suppliers product lists online.
gummybun Senior Member Joined: 15 May 2008 Posts: 21 Location: canada Expertise: I like coffee
Posted Sat Jul 12, 2008, 2:07pm Subject: Re: CMC Machine Lever Hybrid (renamed post)
So... after a couple of exchanges with Doug from orphanespresso, I had several O rings and a couple of U gaskets in hand and went to work. He also supplied instructions and some very nice 3M adhesive silicone (?).
First I slipped on the U gaskets... They were tight in the cylinder and did not turn on the piston but after applying Dow 111 the cylinder fit seemed a bit loose. In operation the U cups leaked downwards at 0.2 Bar and by the time the boiler element cut out at 1.25 Bar I had a cup of water out the bottom, 2 - 3 drops out the top. Top stable at 1 drop per motor cycle - bottom did not seal itself after ten cycles so I presumed to quit and try O ring W/ Tape packing.
After some testing I put the lower ring (which went on to EXACT match of outer diameter to the U cup without packing) with 1 wrap of tape with zero stretch and replaced O ring. The upper O ring which seems to bear less load I put the tape on with some 'strech' to reduce the sectional area.
This combination holds easily to 1.25 bar (has bounced to 1.4bar) W/ no seepage.
Success on the gaskets! Thank you Doug!
The motor seems happier now that it used to - but that could be the residue of the Dow 111. The Crema is (after adding thickness to the lower gasket) slightly better that it used to be - but this machine has never supplied much. I should be looking to other ways to improve that I guess, but the nature of this mechanism does not allow for adjusting the 'pull'. I will need to consider this further.
So for anyone interested... I attach a link to a video clip of the little motor that could, kinda...
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