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Puuuuuuurrrrrrrge

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One of the major advantages of the diagonal heat exchanger boiler in the Lapera is that there is a separate water path to the group. This means that the water from the boiler is not used to actually make coffee. If you have ever seen the inside of a well-used boiler, you will know why this is a good thing. The major disadvantage of the diagonal heat exchanger boiler from a fabrication point of view is there is a separate water path to the group. The separate path requires a second chamber that passes through the boiler – a volume that pierces another volume. This means, topologically speaking, that instead of there being just an inside and an outside, there are two insides and one outside – three surfaces that have to be protected simultaneously during welding where they intersect. When welding from the outside things are fairly easy: cover all the holes, fill all the interiors with purge gas and the gas from the torch itself protects the exterior surface. But what if you want weld from the inside (which we do, because it’s waaay better, trust me on this)? One of the solutions is removing all of the oxygen from the room in which the welding is taking place. But this, oddly enough, is not very popular with the people doing the welding. Other solutions require some kind of localized, gas-filled shroud that covers the exterior of the parts being welded. This can be more or less complicated depending on the shape of the parts that are being assembled. The boiler is a bit on the complicated side of the shape scale, so the shrouds, which also have to fit in/around the jig that holds the parts, are a bit, well, tricky.

Cutaway of the boiler – one volume piercing another creating a separate path for fresh water to reach the group. (The casting is (unfortunately) not pink in real life. Were that it were.)

Shrouds in place to protect the outside of the inside of the inside.

The shroud for the lower end of the heat exchanger (HX) is straightforward-ish. The only minor complication is that the HX tube does not pass exactly through the central axis of the main boiler tube, so the radius cut through the shroud is not quite symmetrical. After welding an end cap onto a small section of square aluminum tubing, the radius cut is easy enough if you have a CNC mill. Which, lucky children that we are, we do.

Quite a few bits of turned and threaded lumps of brass and various adaptors later and, good-enough-for-not-very-close-friends-and-family-whose-company-you-don’t-particularly-enjoy-but-keep-asking-you-to-weld-this-piece-of-their-neighnour’s-friend’s-dishwasher notwithstanding, one lower end purge shroud.

Where things get a little more challenging is at the top end of the HX with the new boiler casting. Both of these purging shrouds, it has to be said, were a bit of an afterthought in that they were thought about after the alignment jig was built. Both of the shrouds could have (and should have) been integrated directly into the jigs themselves. Last time I had my eyes tested, I was shocked to fined out that I don’t have 20-20 foresight.

Not having the right size of tubing on hand, I thought it would be quick to weld a few scraps of angle together.

Yeah, well, not so much. I had forgotten just how hard it is to weld aluminum. It took an entire morning of failing to weld with much swearing, vaporizing of electrodes and grinding out of contaminated welds before I remembered that welding aluminum is like going to McDonalds: I go to McDonalds about once every four years in order to remind myself why I don’t go to McDonalds more often. Also akin to a trip to the Scottish restaurant, once it is in the past (and you machine away most of the mess you make) it is just a bad memory.

A perfect 60 degree angled cut through the not exactly perfect DIY square tubing.

Looks like something. Don’t know what yet. But it definitely needs a cap. Yup.

Now we just need a knife.

Sorry…
…This Old Tony.

And a couple of flanges (close your eyes if you don’t want to be exposed to the welds – but cut me some slack, it is just a jig for Pete’s sake).

Oh yeah, machining hides my sins.

And now for a hole and the clever bit.

Laperas have magnets too.

Thanks for reading!

1 – Syrup of prunes

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jig-jig

Aidan Heart’s somewhat unnecessarily controversial sculpture of the mythical figure of púca, half man, half horse – dancing a jig.

As promised, this week’s post is all about jigs (not about jig-jig, despite the title). Well, jigs and purging. When all the parts are finally made, checked, polished, rechecked and sterilized in the autoclave ready for surgery (only mild hyperbole), two more things have to happen before the magic moment when the arc strikes and two pieces of stainless steel become one: they have to held together in the correct alignment and all of the oxygen in the air surrounding the weld location has to displaced or purged – usually with another, inert, gas. This is where jigs and purging come in.

But before we get to the the fancy bits, first some ground-work.

Cutting the stainless tubing to rough length on Soco Xiānshēng. The 3-phase Soco gearhead cold saw, by far the highest quality tool in the building, used to be known as Soco-San but, it turns out, is actually Taiwanese, so this may have been cultural appropriation, inappropriate and/or just wrong. So even though Soco-San sounds better, Soco Xiānshēng it is.

The before: replete with sharp hairy edges, nasty burrs, greasy mill finish, dents and scratches.

The after: squared and chamfered on the lathe, polished and de-greased to within a nanometer of clean-room cleanliness.

Heat exchanger tubes and flange castings ready on deck.

The first alignment jig ensures that the side-to-side and axial orientation of the tube is correct with respect to the flange casting. Kissing cousins?

Now things start to get a little more elaborate: a dry run with test parts of the heat exchanger (HX) and main boiler tube alignment jig. This setup fixes the depth of the HX through the main boiler tube and ensures that the boiler tube is level and aligned with the bolt pattern on the group flange. Ever-ting gonna be nice’an straight.

So I promised purging as well, but I only got as far as jigs and I am already a day late on my deadline. I’m afraid you’ll just have to come back for more.

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Titanic Upgrade

HMS Titanic boilers1

The Titanic, according to my admittedly mildly-unprofessional research, had 24 of these gargantuan boilers, made by Harland & Wolff Shipyard in Belfast (I doff my hat to you and struggle to maintain control of my lower mandible), that collectively consumed 600 tons of coal a day (shoveled by 200 workers!) in order to maintain the ship at cruising speed. 600 tons. I’m gonna say that again: 600 tons. 15 Jumbo Jets. A day. Mind boggling. So to describe the Lapera boiler upgrade as Titanic is a bit of stretch. OTOH, the Titanic’s boilers were only in service for 4 days and 3 hours (if you include the brief period post-iceberg) so we are already well ahead in that regard.

So why a blog post about this? Well, the boiler has undergone a major design revision for the second edition and, as it is by far the most complicated part of the machine and is completely unseen hidden away inside, it deserves a little more narrative-intensive attention and continuity than the Gram can provide. This will require backing up a little so if you have been following the stream there will be a little repetition to allow the narration to catch up with the intervening flow of time (time only going the one way and all that (another corollary of that pesky Second Law of Thermodynamics)).

The biggest and invisibilest upgrade to the boiler is the change from 304 stainless to 316. 316 is generally and significantly superior to 304 in terms of corrosion resistance mostly because it contains a much higher proportion of nickel. The high nickel content makes it quite a bit more expensive than its baby brother. Which may, or may not, be a factor explaining its non-universality in coffee machine boilers. No judgements here. Just saying.

So on to some of the bits and pieces, of which there are a quite a few, that make up the beating heart of the Lapera machine. First up: the main boiler tubes. Cutting these tubes, or rather finding someone to cut them without screwing them up, has been, until recently, the second-greatest problem / source of irritation since the start of this project in 2016; second only in hassle-quotient to the foundry work. Here they are, cut on an completely over-kill bus-sized lathe this time around because I cannot, to save my life, find anyone with a laser tube cutter who will do this correctly. Done also, despite the 500% increase in the price of nickel in March and subsequent collapse/suspension of the London Metals Exchange where all the world’s nickel is traded. (The causes and ramifications of this is a fascinating story btw. At least to me.)

Close-up of the engraved logo. These are a whole other source of complexity as the final appearance of engraving is very dependent on maintaining a consistent depth of cut -which is extremely difficult to do on a solid that deviates at all from its Platonic ideal. This was trivial when the tubes were laser-cut. Don’t get me started.

Next but not least are the threaded inserts that are welded into each opening in the boiler wall to provide ports for all the comings and goings of two flavors of water phases. This package contains an infinite number of said inserts, which is surprising because it (ie. the package) fits comfortably on the table.

They seem to fit ;) Who knew?

Ok, now that we are more or less caught up. Here is something new (and quite exciting if you are into that kind of thing) to end today’s post: a cast 316 stainless group flange. This casting replaces the original flange that was a built up from individual pieces of sheet metal, all of had to be cut, machined and then welded together. The neck angle is also integrated into the casting which promotes precision of the boiler weldment by a considerable degree. Oh boy, this is soooo much simpler and simpler is soooo much better.

A little QC and a few corrective measures on the all-important flange faces.

The next post will be about jigs and purging I think.

1 – advanceair.net

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Laying the keel

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“And I can recall our caravel:
a little wicker beetle shell
with four fine masts and lateen sails,
its bearings on Cair Paravel.” 2

The Gist.

We make things, unlikely things, in small quantities, mostly by hand, and in a place where it is expensive to do this. The second edition Lapera DS is available now for pre-sale and the price is $12k Canadian. This is a lot by any measure, but not, we feel, and if you understand the process, by any means excessive.

The Longer Version.

I grew up in England in a place where they used to build working sailing ships. It was on the estuary of a minor river and the boats were smallish, made of wood, and slightly dogged. The pubs had nautical names and low tide revealed a collection of rubber boots claimed from the unwise and unwary by the estuary mud. There was a rose-covered bower at the bottom of our garden made from an old rowing dinghy, its stern buried in the ground, and a mysterious sail loft, far larger than the surrounding houses, towered over the garden wall. All that was left of the industry along the waterfront was a collection of empty sheds, crumbling quays, collapsing slipways and a strong air of pathos – now of course all erased by rather unimaginative imitation Victorian housing estates, definitely colder, if not also sadder than what was there before. As with many other places in the West, industry, not to be confused with industriousness, has moved on: where I come from they don’t make much of anything anymore.

I like boats. You may have noticed. There are similar distinctions to be made in boat building as there are in the making of coffee machines. There is a world of difference between “a silent, sweet sailboat slipping through the cool water”3 and a hole in the water lined with wood. Unlike espresso machines (no matter how you feel about your morning coffee), boats have that edge of life-and-death about them: if the water is cold, if it is deep, and most especially if it is angry, you very much want to be in a tight ship and not a wood-lined hole. Both coffee machines and sailboats are outdated technology: one is essentially a steam engine and the other has, well, sails. Coffee machines however, unlike sailboats (beautiful and graceful as they may be), retain a deep relevance to contemporary society: rather more people drink coffee at work than sail to get there. Ultimately, both sailboats and coffee machines are cultural as well as technical objects, inextricably tied to their time and place and to the people who make and use them. How something is made, how deeply its maker understands it and how closely that person is connected to the people who will ultimately use it, are, in my view at least, important. Put simply, culture is difficult, if not impossible, to outsource.

The city of Montreal dates back to the French colonial fur trade and has always been heavily enmeshed in the textile industry. My first three studio spaces in Montreal were in former textile and fur lofts in the old part of the city. The building in Montreal’s Mile End, where Laperas are made, was a leather goods factory (which had been variously and previously: a car wash, a body and transmission shop, a gas station and a stable). Historically, Mile End served as a gateway to successive waves of European immigration. After the second world war, the textile industry grew rapidly until it drew a nearly twenty-thousand strong labour force from the mostly European diasporas (Jews, Greeks, Portuguese, Italians) of the immediate surrounding populations. As with many other kinds of manufacturing, low overseas labour costs coupled with dirt-cheap containerized shipping led at first to the slow decline and then the rapid collapse of the local needlework trade. The loss of tens of thousands of jobs almost overnight had a huge impact on the people who worked there, and left a ghost town of empty factories. Into that vacuum rushed the artists, tech startups and other post-industrial actors in search of cheap space. Now the main industry in the area (other than flat whites) is video games; as about as post-industrial as it gets. The vast flow of European immigrants has left its mark on the neighborhood in the form of churches and synagogues, bakeries and delis, the world’s best bagels (sorry New York, you’re just wrong) and, of course, proper coffee.

Da capo al fine is an Italian term (all the good ones are) in music, meaning “repeat from the beginning” (literally “from the head to the end”), or, as Humphrey Bogart actually didn’t say in Casablanca: “Play it again, Sam.” So, after a few months spent sweeping under the tables, sharpening the chisels and polishing the chandeliers, it is time to take it from the top. We have come full circle and are laying the keels of the second edition Lapera DS: twelve serial numbers from 0010 to 0021. Based on the experience gained during the production of the first edition and the feedback from the Founders’ Circle owners, this edition will have quite a few tweaks to improve, refine and better what can be improved, refined and bettered. So we’re playing it again, Sam, only a little bit better. The price, from beam to beam and stem to stern, is $12k Canadian. A lot, I know, but they don’t build ’em like this anymore. The edition should ship, if all goes well, in the first part of 2022.

For aforementioned unscientific and capricious reasons, the majority of this edition is already spoken for. There are still a few machines in search of a good home however, so please get in touch if you would like one. 

Thomas

(1) Howard Chapelle, 10 ft Rowing and Sailing Dinghy
(2) Joanna Newsom, Bridges and Balloons
(3) Annie Proulx, The Shipping News

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Launched

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“There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don’t know. But there are also unknown unknowns. There are things we don’t know we don’t know.” 2

Well, here it is: the missive I’ve been promising for quite a few years now – the one in which I announce the price and the pre-sale. This is it; the moment has finally come. Sort of.

Very short summary if you aren’t interested in / don’t have time for the medium-long read:

1st thing: This is new. There may be problems. Or there may not.
2nd thing: I’m giving them away (ish).
3rd thing: The pre-production Founders’ Circle Edition Lapera DS machines will cost $8888.88 CAD plus shipping.
4th thing: The next ones will be more expensive.

Before we unpack all of that, please indulge me in a minor digression.

Not too long after graduating from architecture school I put a perfectly good career designing bridges and office buildings on hold and maxed out my credit cards to go on tour with the band. The band in this case being the first work that I had created with another artist: the Symphony for Dot Matrix Printers3, a half-hour long orchestral performance for obsolete office equipment. Fast forward twenty years, after many art projects that investigated questions of technology and obsolescence, and an awful lot of time spent looking for good coffee while on tour, it occurred to me that coffee is one of the very few areas of everyday life where steam engines, i.e. technology from the 18th century, are still considered cutting edge. And so began my third career.

Actions, or so the aphorism goes, speak louder than words. Whatever you may think of his actions, you must allow that Donald Rumsfeld, Secretary of Defense under George W. Bush (remember him?), has a way with words. His quote about the “unknown unknowns”, possibly a bit long to be an aphorism but getting there, neatly encapsulates and conveniently compartmentalizes all knowledge and identifies a distinct category of events which are, by definition, unforeseeable. The lesson being that you must plan for every eventuality knowing that you cannot know all the eventualities. Given who he is and how that all went, the irony of the implicit caution against hubris is, to me at least, rich.

The new Lapera machines have been tested, very thoroughly and rather strenuously, in the controlled conditions of our atelier. I have tried to anticipate all of the problems, from bad water to cosmic rays, before they arise. But what will happen when they venture out on their own into the wide and wonderful and dangerous world? What will happen when they are left alone with your ten year old nephew (no, don’t do that, bad idea – “oooh, a catapult!”). What will happen when someone leaves a pound of butter to soften for baking on the cup warmer and then gets distracted by an Oprah re-run? It is possible, as with all designs entering this Rumsfeldian world, that something not immediately apparent may present itself at some point in the future. Or it won’t. Who knows? At this point there is only one way to find out.

At the beginning of 2016, sitting by a pool in California, I drew the design for the main casting of the Lapera group in my sketchbook. Because, well, that’s what you do when you sit by the pool right? I started with the group casting because it is the most difficult component to make. If I could make that, the rest, I thought at the time, was eminently doable. I also thought that it would take about eighteen months or two years to complete the project. Since then, other than some short breaks teaching architecture and showing at art exhibitions, I have done nothing but work on realizing the DS. Five years is a long time: more than 10,000 hours working a regular nine to five – which of course this job is not. Five years of running costs of my studio. Five years of investment in the materials and labor necessary to iterate the design. And what is that all worth, what did it cost? Suffice it to say that even if I were to charge ten times the amount that I am asking for this first edition, I won’t come any near to recouping my costs. But that is not really why I am doing this. This is not a sensible project. Nor am I, it would seem, a sensible person. Who quotes Donald Rumsfeld in a product launch and suggests that early adopters are potential canon fodder? What you are buying is not so much a coffee machine as it is a love letter to a way of making things that is exceedingly rare today. A work of art. A piece of me.

So this release, the Founders’ Circle Edition of nine single digit serial numbers, fully functional prototypes if you like, is for the risk takers, the early adopters, the beta testers, the kind of people who are willing to put their faith in me. And it is priced accordingly. Of the nine single digit machines, two, I am very proud to say, have been sold into some of the most important private collections of coffee machines in the world. The remaining seven pre-production DS models are available for purchase at the initial price of $8,888.88 CAD (that would be Canadian dollars, U.S. Dollar’s baby brother).

I obviously work very slowly and it is not my intention to scale up the production to the point where I have to forego the level of quality I need in order to get out of bed in the morning. It is unlikely that production volume will exceed the dozens for the next year or two. This means that this price is not sustainable over the long term. Consequentially, the price of the next edition will start with a one and may or may not have any eights in it at all.

If, after doing and saying all of this, I am fortunate enough to have more than seven people still interested, the criteria for deciding who gets one will be thoroughly unscientific: first dibs will be given to the insiders who have been following the project since its beginnings as a series of posts on a coffee forum, the people who have lent a hand and offered encouragement along the way, and the people who I think will take good care.

So who wants one? Just say so and, this time at least, words will have the upper hand.

Thomas

(1) Dream Boat, Monastir, Tunisia, 2018. Available as an NFT for $69,346,251
(2) Donald Rumsfeld
(3) You can look it up. It won a bunch of awards.

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If it ain’t Baroque…

If it ain’t Baroque… don’t fix it.

This morning, I re-read Adolf Loos’s monumentally amusing 1913 essay “Ornament and Crime”. Loos of course, didn’t intend to entertain: the colonial and classist condescension was most emphatically ernsthaft. Eurocentric, racist and chauvinist (to the point of effacement) it may be, the essay nonetheless looms large in contemporary design’s collective unconscious. As Wikipedia puts it (with more than mild understatement): “The essay is important in articulating some moralizing views, inherited from the Arts and Crafts movement, which would be fundamental to the Bauhaus design studio, and would help define the ideology of modernism in architecture.” The central thesis is that ornament is not only wasteful (and therefore immoral) it is also culturally backward: the more ornament you like, the less civilized you are.

Aaron McGruder The Boondocks 1999

A particularly howl-worthy passage:

“Tattooed men who are not behind bars are either latent criminals or degenerate aristocrats. If someone who is tattooed dies in freedom, then he does so a few years before he would have committed murder.”

Lot of, errr, degenerate aristocrats about these days it would seem.

One can’t help thinking that Loos wouldn’t have been a particularly fun guy to be around. Quite apart from hating the heart shape of heart-shaped gingerbread:

“The vegetables [twentieth century man] likes are simply boiled in water and then served with a little melted butter. The other man doesn’t enjoy them until honey and nuts have been added and someone has been busy cooking them for hours.”

Tell that to Jamie Oliver.

Now where am I going with this? Anyone who has been following this thread will know that my design aesthetic is, shall we say, somewhat austere, and that ornament is, more  or less, anathema (less being more and all of that).

Separated as we are by more than a hundred years from Loos’s century, it is both unfair and conceptually fuzzy to judge him by the morals of ours. In short, he is a product of his time and I’m sure that in addition to being a pompous ass he was a good dad. Or not. What is certainly true is that his thinking both presages and underpins a large part of twentieth century design. Without Loos there is no Mies.

To be continued.

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Houston, we have interlock

© NASA, SpaceX, & that Elon guy no doubt, but he steals art to put on his coffee mugs, which he sells, so I feel OK about this.

Houston, we have interlock. “Interlock”?. Interlock is an engineering term which refers to two mechanisms that are mutually dependent. That is, one mechanism must be in a particular state if the other one is to operate and vice versa. A good, reasonably high stakes example of this would be, say, not being about to push the un-docking button while the door of your space capsule is open. There are many ways to achieve interlock, the un-docking button in question may be programmed to do nothing until a certain set of conditions are reached, but in its simplest and, for me, most elegant form, it is achieved through mechanical design and topology. For example: a dangerous machine that requires the operator to activate two separate switches simultaneously, thus ensuring that both of his/her hands are clear of the mechanism. Or the so-called “dead man” switch which must be actively maintained in the on position by the operator in order to keep the engine engaged, thus preventing runaway trains if the operator falls asleep or, er, dies.

At a more this-is-not-rocket-science level, how do you ensure that an electrical device is safe when you remove the cover? Of course, you can put a warning label on it…

…or, you can design the topology such that it limits or eliminates the possibility of error.

Even though the controller for the machine doesn’t have too much to do, it is still a mains-powered device. The two connectors on the bottom row are for power and the solenoid coil for the auto-fill, both of which are mains AC and therefore potentially dangerous. The top row is for the sensors and the interface, which are low voltage DC. The first thing to notice is that the connectors for the two rows are different. There is no way to plug a high voltage plug into a low voltage receptacle or the other way around. The green connector sets themselves are made of up two gendered halves: a female receptacle with male pins and a male plug with female sockets.

The male pins are exposed and could, at least potentially, come into contact with your hand, while the female sockets are completely enclosed by their plastic housing. It is the topology of this paring that determines the way in which it is employed in the design: the male plug with the female socket is the live half of the connection. The male pins in the receptacle cannot be live unless the female plug is in place – and of course, once they are plugged in and are live you can’t touch them.

Finally, the cases are machined with discrete openings for the AC power connectors. This means that the power connectors must pass through the wall of the box when they are assembled and that, conversely, the enclosure cannot be opened, exposing the live circuits inside, if it is plugged in!

Of course, that only lasts while those two tiny strips of plastic that increase the genus of the surface topology of the enclosure by two are intact. And all bets are off if you use the machine in the bath; idiot-proof being a relative term.

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hot porridge

Hot Porridge, Hannah Clarke Preston MacGoun, 1910

[Ed: re-post from Nov 17, 2018]

The new results in my ongoing quest for Goldilocks porridge (aka boiler-group thermodynamic interaction and stability, but porridge sounds much better) are in and I have to say that I’m rather pleased.

What are we testing?
This is temperature profile of the new boiler with diagonal HX and injector. The boiler and the HX chamber are both made of stainless steel but, unlike the previous Horseshoe HX prototype, the brew reservoir is now bronze (for reference, stainless is roughly 20 times less thermally conductive than copper and copper-based alloys). The diagonal HX configuration eliminates the separation between the HX chamber and the brew reservoir and they both form one single volume of hot water at a lower average temperate than the boiler water. Cold water is injected directly into this volume and the resulting mix, now at a lower temperature, moves on into the group during a shot.

Methodology
Methodology is similar to previous tests: the machine was turned on several hours in advance to make sure that everything is at its ultimate idle temperature. The probes are K-type thermocouples placed in the same spots as prior tests – the only difference being that the brew reservoir now has a dedicated threaded thermocouple socket – no more tape coming unstuck or clamps falling off. Shots are simulated by using a flow restricting valve placed on the outlet of the portafilter.

Shot simulation procedure is:

  • Pull
  • Pre-infusion 7 seconds (lever in down position) –
  • Shot 20-25 seconds for lever to return to the cam inflection point (lever just past straight up and down)
  • Post-flow 10-30 seconds (lever returns to rest position)

Various timings between the shots are tried: 5 minutes, 4 minutes, 3 minutes, 2 minutes, 3 minutes.

Comments
The pseudoScace™ device (puck temperature readings) has too large a thermal mass to give meaningful results for peak puck temperatures when inserted cold. I therefore left it in place, before, during and after the test to minimize its impact. The one second sampling time period is too long to give reliable readings at the moment of the pull. On a few of the shots there is a significant drop seen at the puck at the moment of the pull. I believe that this is due to the piston creating a vacuum as it is raised and drawing cold water back up through the pseudoScace from the waste line. A change in equipment would be required to eliminate this if this hypothesis is correct.

Conclusions and observations
The original Aurora diagonal HX I profiled back in May demonstrated uncanny thermal stability at the brew reservoir, but the group suffered per-shot heat-gain and was slow to return to its baseline idle temperature. These results show that the brew reservoir temperature is dipping significantly but the group and the puck temperatures are, by comparison to the antique machine, rock steady. The maximum overall delta at the puck is 3.1 C (between the walk-up and the third shots) but the inter-shot maximum delta is 1.8 C (the minimum inter-shot delta is 0.5 C for 2 minutes between shots).

Summary
So, to summarize: best performance at 2 minute intervals, significantly lower puck temperature fluctuation than the antique machine and little to no group heat-gain. This, I think, may be a slightly better mouse trap – though not really by design, rather by accident of the thermal interaction of the materials. I’m not going to complain.

If you will permit me, and at the risk of tooting my own horn:

Courtesy of UC Davis, Special Collections
Title: Magazine ad for Bank of America: hammer and nail montage.
Creator/Contributor: Halberstadt, Milton, Photographer

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Goldilocks part 3

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 [i]before the end of the recovery time,[/i] 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 [i]no matter when it is pulled[/i]. 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.