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.
It seems to me that the design of mechanical systems might be described most simply as the selection of a set of idealized rules that, taken together, define how objects are allowed to move with respect to themselves and one another. For example: in addition to turning, the front tires on your car can rotate to the left and right (the steering) and move up and down (the suspension), but bad things have happened or will likely happen if they move either along or perpendicular to the direction of travel of the car. These rules or constraints are most often defined in three-dimensional Euclidean space in which there are three imaginary axes, each representing a single dimension, that pass through the centre of an object and (with engineering’s typical disregard for unintended double entendre) 12 degrees of freedom, or ways in which that object might move with respect to the axes: it can be translated, moved like a chess piece, in six directions, left-right, front-back and (unlike normal chess pieces) up-down and rotated backwards or forwards around the same three axes.
So before I get to the first production run of the pieces of the Lapera lever group, I thought it was worth revisiting the prototype piston assembly that I made some time ago. Rather than the fixed piston head and piston rod design typically used on most contemporary lever groups, I opted for a slightly more complicated articulated or floating-head design. The downside of complexity of course is that it always comes at a cost: more parts to make, more parts to assemble. The upside, which I think considerably offsets the disadvantages, is that the articulated piston is self-aligning: it automatically compensates for angular misalignment and eccentricity between the axes of the cylinder bore and the piston rod. This results in loads and consequent wear patterns on the piston seals that are more symmetrical. Even wear on the seals promotes seal longevity – which is a good thing!
The piston mechanism is perhaps best explained by an analogy to a part of the human anatomy: the wrist. Your hand is free to wave from side to side (like the Queen),
forwards and backwards (like Mikey)
and also to rotate (although this is not actually a design requirement for the piston assembly but I couldn’t resist the plastic, solar-powered Queen).
These rotations, or degrees of freedom, have limits of course; otherwise it gets really weird and creepy (think The Exorcist). In addition to rotating, the wrist permits the piston to translate laterally – similar (though not actually via the same mechanism) to another body part: the head.
So the piston assembly is sort of like a wrist, or a head, or maybe a neck. I don’t know anymore. I guess body part analogies only get you so far when trying to describe mechanisms. But I, at least, enjoyed the animated gifs. The upshot of all of this is that the chosen set of constraints embodied in the design of the wrist allow and restrict the 12 different types of motion and permit the force from the seals as they press against the cylinder wall to rotate and translate the piston into perfect alignment with the bore. Or perhaps you got it months ago and I could have saved myself a lot of writing by just posting another gif:
Here is a reprise of the fabrication process for the prototype of what I am still insisting on calling the wrist. Starting from a piece of 2″ C360 brass round bar stock:
Two slight angle cuts on the tip approximate a radius – this is quicker to setup than cutting an actual arc and makes little difference to functionality.
Then, using a cut-off/grooving tool, we add an undercut below what will be the flange. Spoiler: this is the clever bit of the design.
Another wider groove is cut above the flange to create the boss that will align the spring.
Then the part is cut off the stock…
…and flipped around to be drilled…
…and tapped with an M10 thread.
Then the part is moved over to the milling machine to complete the remaining features. This process starts with finding the centre with a touch-probe.
Then three clearing holes are drilled in the flange and boss.
After a little cleanup – a finished wrist prototype.
And here, with some very slight dimensional tweaks to adjust the permissible amounts of rotation and translation, is the production wrist part in the final material – AISI 304 stainless steel.
Mmmmmm – shiny 🙂
Next post will be on the piston. Can’t bear the suspense myself.
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.
A small but nonetheless significant milestone was past today: the installation of the boilers! This what the assembly area looked like in the morning:
All of the difficult-to-access-once-the-boiler-is-installed parts are in place and it was time to put make the transition from seemingly random collection of wires and hydraulics into something closer to an actual coffee machine. Imagine!
One small detail that isn’t visible to the naked eye is the low-friction cushion tape that prevents the frame from being damaged by the boiler flange.
Removing the boiler is not an operation that will happen many times over the lifespan of this machine (at least that is the plan), but preventing damage to the paint at a connection adjacent to a(n at least theoretically) consumable gasket is a good idea…
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:
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 stabilityat 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
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…
I have an indelible childhood memory of watching reruns of serialized television from the 50s in black and white. At the end of each episode the heroes always seem to be in an entirely intractable position: hurtling towards certain death as the car / rocket ship plunges to the ground or tied up as the bad guys abandon them to their fate as the building burns / volcano erupts. How do they escape? “Find out next week” on …
During the interlude since the last episode (during which I can assure you that the heroes have been frantically filing away at their shackles) I took stock. Here is the state of the production:
Frame – complete & painted. 100%
Cable harness – all modules of the cable harness are complete. A few remain to install with the bodywork. 100%
Controller – four out of five boards designed, tested and in production. One board under design revision. Machining and labeling of enclosure, assembly and installation remain. 75%
Firmware – functional with a few small problems to resolve before it is “good enough” as firmware is never “finished”. 90%
Hydraulics – the most complicated part of the plumbing including all tubing runs connected to the four lower boiler ports, the HX, solenoid, manifold and drain are complete. Six upper ports remain. Of these six, three require fabrication of tubing runs. 70%
Boiler – complete & installed. 100%
Group – The main casting is complete (no small milestone), machined and honed. All the fixed components are complete and on the shelf. The spring is out for quotes as are the parts for the piston assembly. One part remains to fabricate in house and then, once all the parts are in, the group can be assembled. 70%.
Bodywork – Two pieces remains to fabricate and one may have to be revisited. 70%
Millwork – LRFs are complete and installed. All of the cup rail parts are fabircated and finished and are waiting for installation. Tap handles are machined but need to be assembled and finished. Stock has been prepared for making the lever and portafilter handles. 85%
After final assembly is complete there remains testing and packing… in short, there are still a few episodes of this particular series left. How many? Find out next week on ….
Left Ring Finger? Long Range Forecasting? Low Resolution Fox? Nope, definitely not the last one (look it up (yet another minor moral quandary about whether something sexist can also be amusing; probably not allowed, but I digress)). No, rather, I offer some small observations on Little Rubber Feet!
LRF are perhaps something that you might not have spent a lot of time thinking about, but they are ubiquitous and surprisingly important. They are a crucial component of almost every single contemporary household object: from the chair I’m sitting in, to the computer monitor in front of me and even the keyboard I writing this with. The underside of your mouse (if you still have one)? LRF, albeit very small and not at all rubbery. You might say that LRF, if one were to stretch the definition just slightly, are the industrial design equivalent of building foundations: the point(s) at which objects touch the surface they rest upon, negotiating the transfer of the load, evening out imperfections and keeping delicate surfaces away from harder ones. They come in a myriad of shapes and sizes. There are hard ones that slide, soft ones that grip and everything in between. In addition to being made from every kind of natural and artificial rubber and plastic imaginable, they also are made from wood, glass, felt, cork and occasionally even metal. The most special LRF are the orphans that turn up on the floor or being chewed on by your pet and or child. They only reveal their origins six months later when you finally find the lamp that now both wobbles and scratches the table. These are also the same kind that, origins revealed, you are guaranteed not to be able to find again or to just have finally thrown away. Not me though. I have a special LRF drawer.
The scale of a single group lever machine comes with a few challenges. Both the porta filter and the lever itself require the user to apply relatively large amounts of force to the device. Ideally, it should resist these forces without moving when they are applied. Although single group machines are quite large and heavy compared to most items that might sit on your counter, they are featherweights compared to multi-group machines. These are just in, custom made from a low-durometer self-adhesive backed 3mm silicone rubber. The weight of the machine forces the soft material to conform to minor imperfections in the supporting surface vastly increasing the contact area and friction. Result? It grips like a barnacle to a rock.
So Stravinsky’s ballet caused a riot… perhaps it was the shocking juxtaposition of pagan and modern Weltanschauungen, maybe the audience just didn’t like the music. What can I say? Springs are contentious. With that warning, I shall begin trying to unravel the (minor) mysteries of one particular spring.
A little more than a year ago, it was brought to my attention that replacement springs for the Brugnetti Aurora lever group were no longer available. I checked a number of suppliers and looked for substitutes without any success and I immediately went to my local parts dealer and bought the rest of their stock – a shockingly large number: four.
This is a problem if you are me and want to make new groups, or, if you are not me, repair old ones. So I took the dive into spring design and started to think a bit more carefully about a part that I had presumed was going to be “off the shelf”.
I have since come to the conclusion, for a number of reasons that will further elucidated, that the spring that was sold to me as a replacement for part number A.29 for the Aurora group, may not be, well, a replacement for part number A.29.
When I changed the spring on my first machine (well before I embarked on this voyage deep into the jungle down the Congo River) I noticed that the new one was a little taller than the original, making it quite a bit more difficult to install. Installed it was however, and I thought no more about it. That particular machine dates from 1987 and was rebuilt by a local dealer in the mid 90s – but may well have kept its original spring given how much of a hassle they are to change.
Under normal operation, springs will deliver an amount of force that is directly proportional to the distance they are compressed: F = kx (where F is Force, x displacement and k is the spring constant). Put another way the spring constant is simply how much force the spring imparts per unit of compression. So determining the spring constant can be done by measuring force versus displacement. This is the setup used – the force gauge (i.e. bathroom scale) isn’t ideal because of the built-in “intelligence” which automatically tares (zeros out) small readings and shuts off the display, but it does measure up to 175Kg. Displacement is measured using a digital height gauge (not shown) that (as so long as the same datums are used and the gauge isn’t re-zeroed) provides more accuracy than required with enough precision (I can never keep those straight).
I believe that I have identified three different springs that were installed in the Aurora group at various stages:
The replacement “after-market” spring from the local dealer which has an uncompressed length of 133mm. Antique spring #1 – which has an uncompressed length of 128mm. Antique spring #2 – which has an uncompressed length of 116mm.
Here are the compression versus force profiles of those three plus a fourth new prototype spring.
The two trials of the after-market 133mm spring suffer from some measurement error – i.e. if you extend the lines back towards the X axis, they don’t intersect the origin coordinates; which they should, as zero spring displacement results in zero force. If they were to be normalized (i.e. shifted down until they would intersect the origin if extended) you can see that they correlate closely with the all of the other trials except the Antique 128mm. In fact the spring constants (calculated using the average slope of all the data points in each trial) for all but the 128mm spring are around 60 N/mm whereas the 128mm is significantly lower at 44 N/mm.
However, the fact that the springs are different lengths is not a minor detail. As the geometry of the piston assembly remains the same, the springs are all compressed to the same size when they are in use i.e. they have an installed length of 96.25mm (corresponding to the lever in the up position) and a fully compressed length (when the lever is in the down position) of 75.5mm.
Installing a springs of different lengths will mean they are operating over different force ranges. The corresponding pressures that the piston will deliver can be easily obtained from the equation P=F/A (where P is pressure, F is force and A is the surface area [19.63cm sq for the 50mm diameter piston in the Aurora group]).
Spring constant (N/mm)
Force @ fully compressed (N)
Force @ installed length (N)
Presuming that you find tables at all interesting, some interesting points can be drawn from the one above (although now we are getting into subjective and therefore contentious territory). The first line shows that the replacement after-market springs from the local dealer are very likely incorrect as their theoretical operating range is 18-12 bar. I think most people would agree that this is too high. The case for these springs being incorrect is strengthened by the fact that a design analysis of that spring configuration, (i.e. the spring constant, wire size, number of turns, end conditions etc) results in a non-compliant design when used in this application (i.e. the installed length and travel) meaning that it is likely to fail to perform as expected or simply to fail over time.
The second point of interest is that the two antique springs, despite their different properties, yield very similar pressures in the installed configuration – approximately 12bar maximum and 6-7bar minimum. Without knowing more about the provenance of these particular parts, it is hard to know whether they have changed over time or whether they are still operating as designed. However, based on the subjective results of the quality of the coffee that the machine produces when it is operated over this pressure range, I believe that this was the design intent. Further testing of other old springs of known provenance would be helpful to confirm this hypothesis.
For the prototype I chose to use the shorter ~116mm format because it is significantly easier to install and opted for a similar 12-6bar range at the installed configuration. The new spring should be a drop-in replacement for the old Aurora groups.
Prototype Lapera spring on the left, 18bar monster on the right. We fervently hope this little one doesn’t dance herself to death.