Building a lever machine.... from scratch - Page 41

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Team HB

#401: Post by samuellaw178 »

Amazing Thomas. :D This temp study is a sign the prototype is well and truly working.

If only Mama bear had bought that induction cooker (cartridge heater) when she was shopping, then it would have been too easy to keep the porridge warm enough for everyone... :P :P

Looking forward to the next part of the story!


#402: Post by Paolo »

samuellaw178 wrote:
If only Mama bear had bought that induction cooker (cartridge heater) when she was shopping, then it would have been too easy to keep the porridge warm enough for everyone... :P :P

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#403: Post by bidoowee »

samuellaw178 wrote: If only Mama bear had bought that induction cooker...
Papa bear does the cooking in my house ;)

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#404: Post by bidoowee »

It is high time for more porridge!


Illustration by Pervprude

Several days after I did the first tests, it occurred to me that the horseshoe tube that I had made when I built the boiler was not the same as the one in the Brugnetti boiler. I wasn't really thinking that hard about how a heat-exchanger actual works while I was making it. So I took apart the boiler (again). This is the original tube, nicely blackened after a few months of service:


I measured the interior volume of the 'Papa Bear' version and compared it with the volume of the vintage HX horseshoe (modeled in CAD): 115ml for the vintage and 135ml for Papa Bear. So I put Papa Bear to the bandsaw, and cut him down to make Mama Bear.



Blue - Boiler
Red - Brew reservoir
Purple - Group neck

(The data for the neck was very noisy for some reason that day - the rapid deviations do not reflect what is actually going on.)

Despite having the same volume as the vintage tube, 'Mama Bear' doesn't behave the same way. The peaks in the brew reservoir temperature are similar to Papa Bear, i.e. around 5 degrees, and recovery times are about the same. It should be noted however, that with adequate recovery time, the neck temperature shows a high degree of stability.

I then modified the horseshoe again, lowering the volume to around 100ml (Auntie Bear??) - but the results didn't change significantly. So I decided that drastic measures were called for: 'Baby Bear' - roughly 60ml volume which is about half of the vintage.



Though the results are better, there are still spikes in the brew reservoir temperature.

Time to alter the Goldilocks plot line.

Introducing 'No Bear'! Partly to make sure that I wasn't entirely out to lunch but also to measure the other extreme, I connected the supply to the brew reservoir directly to the mains, bypassing the HX and injecting room temperature water into the reservoir. Unsurprisingly the results are dramatic!


Very cold porridge indeed.

Interestingly however, while the neck temperature rises by a few degrees initially, it recovers quickly (less than a minute) and then drops to 2.5 degrees below idle.

Where does this leave us? The concept of the HX is of course to inject (fresh i.e. non-boiler) cold water through the hot water in the boiler in order to raise it to the 'correct' temperature to feed the reservoir. If the machine has been idle for any length of time, the water in the HX will be at the same temperature as the boiler. Subsequent shots will draw cold water into the HX, which, depending on how it is designed, will consistently bring room temperature water up to a specific temperature (either boiler temperature or slightly lower), as long as the heating element can keep up with the demand. So some not very earth-shattering conclusions:
- Changing the design of the HX will determine the temperature 'profile' of the water delivered to the brew reservoir.
- Somewhere between 60ml and 0ml of HX volume, the water delivered to the reservoir will offset the heat gain and result in equilibrium.

There is one additional question that results from the three bears test: why do identical horseshoes in the vintage and new boilers not exhibit the same thermodynamic behavior? My hypotheses is that materials used for the brew reservoir and boiler are playing a much bigger role than I first thought. Both of these parts on the prototype are made from stainless which is roughly 20 times less thermally conductive than copper and bronze. To test my theory, I put the prototype group onto the vintage machine: compared to the all-stainless boiler assembly, the new group runs around 12 degrees hotter on the copper/bronze boiler. The stainless brew reservoir is slow to acquire heat from the boiler and the water in the reservoir and reluctant to relinquish it to the air or pass it on to the group.

SO.... two rather more significant conclusions:
1 - There should be (or rather, spoiler alert, there is, as will be seen in an upcoming episode) an HX design that meets the requirements of stainless boiler and group combination.
2 - It is time to make a new boiler - using the bronze brew reservoirs that I received a few months ago.

sprint jinx

#405: Post by sprint jinx »

I am sending a thank you to you and your forays into HX boiler designs.
I am on the brink of starting a rebuild of my machine, which is a hybrid of both an HX boiler and a Lever group. I am reading along with interest in your findings.
I am proposing a design that allows for a small block of metal with a cavity inside - to be in between the boiler and HX unit. Water will mix in there and perform the thermo-syphon loop, and also pass through to the lever group. This all works, in my head. I may add temperature control and heating bands or cartridges to the adapter chunk, in hopes of controlling things.

anywho- carry on please- this is encouraging.

Supporter ♡

#406: Post by pizzaman383 »

I continue to be impressed with the way you are approaching this project. You set a plan, try it out, check the results, and then adapt the plan.

I have found in my customizations that the thermodynamics of the various parts work together is one of the most important things to understand.

Hopefully, the change back to materials similar to the original will help. Otherwise, you can make a shift towards controlled heating.
LMWDP #551


#407: Post by Paolo » replying to pizzaman383 »

I too am incredibly in awe of your approach to this project, Bidoowee.

I must say that reading about your exploits in tuning a boiler/group reservoir/group etc to give optimum temperature/quickest recovery etc. for espresso seems to me to be somewhat of a 'black art' :twisted: ....or involve lots of testing/altering and testing and patience. :D

Just as an aside....I have recently become a convert of 'controlled heating'.
I am lucky enough to be in a position of having a friend who trusts me...and has loaned to me his amazing machine. It has a Faema Zodiac lever group from the 1960's which he is using to replace the e-61 group in a modern machine. Amongst other changes, Mike (username Kitt) fitted cartridge heaters to the vintage group.
Lever Espresso Machine Gallery

The heaters enable the group to come up to temperature in 25 minutes from cold...and stay at the temperature that they are set at.

Getting back to the humble Aurora.. I haven't measured any temperatures except for the outer group temperature in my Aurora. Once heated up properly (about 45 minutes) it remains between 70C and 75C...and makes beautiful espresso shots.

I am eager to hear your next instalment, Thomas!

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#408: Post by bidoowee »

Thanks to Porter, Curtis and Paolo for the kind words.
sprint jinx wrote:I am on the brink of starting a rebuild of my machine,
Yes! Yes! Good project - this is the right place to find out everything you need to know - but I think perhaps you are already on the right track by the sound of things.
Paolo wrote:tuning a boiler/group reservoir/group etc to give optimum temperature/quickest recovery etc. for espresso seems to me to be somewhat of a 'black art'
The black part of the art is the stuff that's in the cup :).
Seriously though, it is really easy to get caught up in the numbers and to forget that more often than not the best guide is experience and taste. For a long time, the "technically more temperature stable i.e. better" of my two auroras made inferior coffee; simply because it was running too hot. Stability matters not at all if that "stable" temperature is wrong. There are a lot of variables involved and, until recently, there was no way to do more than basic thermal calculations. Finite Element Analysis and Computational Fluid Dynamics have changed that, but the engineers who designed the lever machines were using slide rules... I suspect that they got there empirically after decades of trial and error.
pizzaman383 wrote:Otherwise, you can make a shift towards controlled heating.
Paolo wrote:I have recently become a convert of 'controlled heating'.
This, I think, is more of a philosophical question. There are definitely ways to increase the stability and decrease warm-up times but all of them involve additional complexity. Cartridge heaters in the group? Better. Separate brew boiler and dual PID? Also better. Temperature and pressure sensors at the puck? Again, no question: better. But all of these things add complexity and expense to the classic boiler+HX+lever group design that I regard as the least complex and therefore most-perfect resolution of the (challenging) technical problems involved in making good espresso. The lever machine is a Haiku on the economy of means.

For my design, the one (admittedly significant) concession to complexity is the addition of a micro-controller - which I would defend because of its combination of ubiquity and utility. Just as electric resistance elements replaced gas burners and electric solenoids were substituted for manual valves so the micro-controller is today's "right" technology for the job of control.

But I think I'm getting carried away... boiled starchy plants is what I was supposed to be writing about this afternoon.

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#409: Post by bidoowee »


The set of the bears. Plate 7, 1664, by Marcus de Bye, after Marcus Gheeraerts I, 1559. Gift of Bishop Monrad, 1869. Te Papa (1869-0001-67)

Though I've run out of three bears analogies, I've stuck with the story's structure: first the porridge was too hot, then it was too cold, and finally Goldilocks found one that was just right. This iteration of the HX caused me to take my hat off, yet again, to the Italians. Many months ago, Dr. Pootoogoo brought a boiler from a later-model Brugnetti to my studio. The flange bolts were so badly rusted that it wasn't ever going to go back into service without replacing them. It happened to be one with a diagonal HX that I hadn't examined before and it inspired my to try a similar concept with the horseshoe HX prototype. I was quite surprised that the 60ml HX (baby bear) didn't deliver water that was cooler than the brew reservoir temperature even though the HX volume was close to the 50ml shot volume. I also started thinking about what the 'correct' temperature for the brew reservoir should be. It occurred to me it might not be the best thing for it always to be the same. For example: if the group is at 75 C and the water coming in is at 102 C, the resultant water temperature at the puck is 92 C (these are roughly the numbers for both vintage machines) and we know that the group gains heat after a shot, let's say for the sake of argument it gains 3 degrees and requires about 2 minutes per degree to recover i.e. 6 minutes. It follows then that for the next shot, if it is to be pulled before the end of the recovery time, it would be preferable to have the brew reservoir water at a lower temperature than 102 degrees so that when it reaches the puck it will be at same magic 92 degrees. Because of the difference in thermal properties of the materials (i.e. the brass group and the water) and their relative volumes (i.e. big thermal mass of brass vs 50ml of water) it isn't a one to one relationship. But it is linear - i.e. it will be a constant times the temperature rise of the group. So at any given time during group recovery, the required brew reservoir temperature is the reservoir idle temperature minus the group temperature rise times some constant. In math not English:

Tbr = Tbr_idle - K(Tgroup - Tgroup_idle)

In other words if the heat gain curve of the group could be inversely mirrored by the brew reservoir, then water will be at the right temperature when it reaches the puck no matter when it is pulled. This is really just destructive wave interference:


If the brew reservoir temperature curve is positive (i.e. there is heat gain), then it will compound the problem of heat gain at the group. But if the brew reservoir temperature drops after a shot, then it will compensate.

The diagonal HX design consists of a large diameter pipe which connects directly to the back of the brew reservoir - essentially increasing the volume of the brew reservoir four-fold. In fact, the concept of the brew reservoir is pretty much gone altogether in this design - the group flange actually becomes one end of the heat-exchanger. A small diameter injector tube runs through the middle of the large diagonal pipe. Line water comes in through the injector too fast for the surrounding water to heat it to boiler temperature and mixes with the water behind the group to get the really stable results that we saw in the earlier testing.

I replicated the basic principal minus the diagonal tube and in so doing figured out why the diagonal design ended up that way i.e. diagonal.


The last kink in the 6mm tubing was only way to thread all the larger diameter fittings onto the injector. And this is a one-way operation: once it is brazed together you can't take it apart again.

Brazed and (sort-of) cleaned.


And here are the results:


Blue - Boiler
Red - Brew reservoir
Purple - Group neck

Now, although the results aren't perfect, it shows that the concept works. The group heat gain for successive (unnaturally) rapid shots has been significantly diminished and the recovery time for the group is less than half of what it was (less than 3 minutes). The length of the injector plays an important role in how much boiler temperature HX water mixes with the line water and consequently in the temperature of the water that reaches the brew reservoir. But, as I said, this is a one-shot fabrication and is too much trouble to alter. It would be much easier to change and/or maintain if the injector tube screwed into a straight length of larger diameter tube that maybe ran directly to the group right through the boiler, maybe on a diagonal...

Wait - someone already thought of that.

Enough porridge already.

Team HB

#410: Post by samuellaw178 »

Some really impressive work going on here. :shock:
bidoowee wrote:Wait - someone already thought of that.
Don't sell yourself short! I think you're still the first one to execute the concept properly (the way of Porridge ftw). As you mentioned, on the diagonal HX the concept of brew reservoir is pretty much non-existent (which needs to be there and stay slightly cooler on subsequent shots to achieve heat attenuation). So technically speaking you're the first one getting close to the holy grail of Goldilocks porridge. :lol:

It's a surprise that your 'Baby Bear' didn't quite do it (such cute looking hx btw). I guess the fluid flow characteristic in the horseshoe HX is more a laminar/plug flow than a turbulence/mixer (something I've been wondering a lot).
bidoowee wrote:Stability matters not at all if that "stable" temperature is wrong.
Well put! That's the million dollar question and I am looking forward to what surprise you have for us to raise the overall temp. With all these great engineering displayed on the thread so far, I am expecting much and won't settle for something mundane like turning up the pressure. :twisted:

Just kidding! But I am genuinely curious what's the plan.

p/s: can you slip fit a telfon injector tube at the HX inlet? That way no weird brazing method needed and way easier to adjust. You can decide where the water exits from the teflon tube as well.