Building a lever machine.... from scratch - Page 9

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bidoowee (original poster)
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#81: Post by bidoowee (original poster) »

The other new part in this package is the bearing shoe(s).



The part that actually carries the load from the bearings is made from aluminum, which is far too soft for the forces involved.
Consequently, a harder material (stainless 304 again) is required for them to roll on.



The parts are dropped one by one into a setup on mill in order to countersink the screw holes.



A nice 1/4" zero-flute chamfer bit with a strong stream of air from the compressor to keep things cool.
304 is in the family of "moderately difficult" steels. The chrome that makes stainless, well, stainless, has the annoying habit of causing a phenomenon of work-hardening, which means that the very act of cutting it can make it more difficult to cut. Care must be taken to select the correct feeds and speeds to cut the stuff properly.

Job done! A nice, satisfying stack of parts.


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bidoowee (original poster)
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#82: Post by bidoowee (original poster) »

Next up: more presents in the mail - I love unboxing!



This is the first batch of machined parts from a cnc supplier I am auditioning for the project.
The parts are individually bagged and/or wrapped in tissue paper and sheet foam.



The first part is what I call the bearing plate, it also guides the piston rod and spring. The force is strong in this one - quite literally.



Then, the piston cap, more about this later.



In the same package I also received copies of the retainer plate. Having it fabricated was cheap enough, and mass-producing it in my shop would have been a lot of work, new tools and a whole lot of chips on the floor to sweep up. Here it is along with the group body and the other new parts.



Couldn't resist photos of the mock-up:







As you may have noticed, the bad news is that the chrome finish on the piston cap doesn't match the group body! ARRRRGH.

Different shops, different finishes. My suspicion is the cast-bronze body has been plated with hexavalent chrome whereas the trivalent process has been used for the aluminum piston cap (for those who are interested, the difference is perhaps best summed up in two words: Erin Brockovich; hexavalent chrome is nasty stuff). The caps could be re-chromed, but that requires (chemically) stripping the existing finish first which is as or more expensive than chroming them in the first place. Total PITA. This one is going to have to be resolved some other way.

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FotonDrv
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#83: Post by FotonDrv »

Thomas, you are truly a dedicated man on a mission!
That Light at the End of the Tunnel is actually a train

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pizzaman383
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#84: Post by pizzaman383 »

I am a little concerned that the SS boiler neck will not pass heat to the group head the same way as the original did. That may have an impact on the temperature management.
Curtis
LMWDP #551
“Taste every shot before adding milk!”

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FotonDrv
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#85: Post by FotonDrv replying to pizzaman383 »

Isn't the OP putting Group Heaters into the Group to ensure temp stability?
That Light at the End of the Tunnel is actually a train

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bidoowee (original poster)
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#86: Post by bidoowee (original poster) »

pizzaman383 wrote:I am a little concerned that the SS boiler neck will not pass heat to the group head the same way as the original did. That may have an impact on the temperature management.
Aha! A man after my own heart. Yes indeed, the stainless is an order of magnitude (roughly 30x if memory serves) less thermally conductive that the brass of the original. For a number of reasons, it is currently not my intention to put additional heaters into the group for temperature stability (learn to walk before you run etc.). Once the boiler reaches temperature, the brew reservoir (the space inside the "neck" of the boiler, which is made from stainless in my design) will, presumably and eventually, reach the same temperature as the existing brass one. In the original design, the group head is actually thermally isolated from the brass flange of the brew reservoir it connects to by an asbestos gasket. The only metal to metal conduction takes place through the four M10 stainless bolts that connect the group head to the flange of the brew reservoir. The vast majority of the heat transfer to the group head is, consequently, through the water in the brew reservoir that is separated from the steam at the top of the boiler by a thin (~1/16") wall of copper - i.e. almost nothing, thermally speaking. So although the brass chamber surrounding the reservoir does get hot, my suspicion is that it loses significantly more heat to the atmosphere (thus cooling the water) than it passes to the group through the four bolts.

Thus, my hypothesis is that the limiting factor is actually the heat transfer through the wall of the boiler to the water in the chamber. I have accounted for this by adding a brass thermal bridge that passes through the stainless wall of the boiler to provide direct transfer of the heat from the steam side to the reservoir side: one end of the "bridge" is sitting in the steam, the other is in the water inside the reservoir.

There is one possible (significant) problem that I foresee with this solution: the (original) brass brew reservoir may act as heat 'storage' (providing a reserve of heat) or as a thermal dampener (helping to stabilize the temperature fluctuations) for the water that arrives from the HX to replaces the brew water in the reservoir when a shot is pulled. Without building a thermodynamic model of the machine, only time and (significant) testing will tell!

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drgary
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#87: Post by drgary »

If your group runs cooler compared to boiler temp than the original, you could have a larger temperature decline during the shot, which could offer more flavor layering than the original -- and vice versa. It'll be interesting to see how this turns out.
Gary
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What I WOULD do for a good cup of coffee!

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pizzaman383
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#88: Post by pizzaman383 »

bidoowee wrote:Aha! A man after my own heart.
I was cautious with my comment because I wasn't sure how much you had considered this. I am glad to see what you were thinking.

I control the temperature of the plate to which the group head is bolted to control the group head temperature. Controlling the heat transfer like you are trying could work, too.

I have tried various combinations of boiler water temperature and steady state group head temperature and I found that those that produce an appropriate shot temperature all work. I look forward to hearing about your testing.
Curtis
LMWDP #551
“Taste every shot before adding milk!”

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bidoowee (original poster)
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#89: Post by bidoowee (original poster) »

pizzaman383 wrote:I control the temperature of the plate to which the group head is bolted to control the group head temperature. Controlling the heat transfer like you are trying could work, too.

I have tried various combinations of boiler water temperature and steady state group head temperature and I found that those that produce an appropriate shot temperature all work.
This is interesting. I find the brew reservoir design in the original very elegant - pulling cold water through the HX to produce slightly less than boiling water to fill the reservoir and maintaining the temperature at idle by drawing heat from the boiler. In fact, the entire thermodynamic design is a tour de force as far as I am concerned: a single heat source is used to meet five separate and somewhat conflicting demands - maintaining group temperature, brew reservoir heating at idle, preheating brew water during the pull, steam delivery and hot water delivery. The only drawback being that all parameters are affected by a change in boiler temperature. The only way to tweak a single parameter at a time is with physical design changes. If your finding (that various combinations of brew water and group temperature work) turns out to apply to this design once it is done, then it bodes well for its coffee making potential.

If not, the fabrication of the boiler could potentially be simplified by separating the brew reservoir from the body of the boiler and (at the cost in complexity of) providing it with its own heat source (and closed-loop control system).

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FotonDrv
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#90: Post by FotonDrv »

Would you have any need for this as a test jig for something? It was brand new and a takeoff from a Londinium L1-p that was manufactured with a dent in the corner, assembled, and shipped to me in a beautiful box displaying the dent proudly. Londinium sent me a replacement ASAP (figures...) so this is a spare that I have no use for.

The red plastic was a test fit for the good top surround and does not come with it.


Free except for the shipping costs.
That Light at the End of the Tunnel is actually a train