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The Mind and Machines of Verna Design By Lino Verna

Editor’s note:
Some brand names become so familiar, it’s easy to forget that they are often someone’s last name. Most Americans recognize that the “Ford” in Ford Automotive Company is Henry Ford’s last name. How about Cimbali? That would be Signor Giuseppe Cimbali. And one of my favorite craftsmen, Reg Barber, is behind the wonderfully executed tampers that bear his distinctive RB logo. As an engineer and espresso equipment admirer, my appreciation of well crafted products extends not just to the end result, but to those who produce them. In recognition of the people behind the products, this article offers you a glimpse of Lino Verna’s workshop where he machines his own espresso gear, including “bottomless portafilters” like those featured in Perfecting the Naked Extraction. —HB

 

First and foremost, I’m a mechanical engineer. And not just by degree—for better or worse, it’s in my blood. That’s the primary mission of Verna Design—mechanical design consulting. However, I frequently like to make whatever I’ve dreamt up, so I also have some fabrication experience, primarily in machining and welding.

What does that have to do with coffee? Well, explaining that requires a little background.

Growing up in an Italian household, coffee has always meant espresso—provided you allow the brew from a Moka pot into that definition (hey, this was 20+ years ago!). However, I never got seriously into espresso from a CoffeeGeek perspective until about two years ago.

Admitting to my espresso-loving peers that I’ve owned a variety of Krups machines (and still do) always gets a few chortles. But about two years ago, my wife mentioned the possibility of buying a new espresso machine—a nice espresso machine. That was like waving the red flag in front of a bull. I spent the next three days surfing the Internet, trying to find the right one for me. Finally I found it, the machine the espresso-lover in me had always been longing for—the ECM Giotto. Well, my wife thought differently. Quite differently! She thought I was nuts, and it would be a cold day in hell before we spent a thousand-some dollars on an espresso machine. (Something tells me I’m probably not the first guy to tell this story.)

However, I was not deterred.

CAD schematic of proposed espresso machine

Was that inspiration or perspiration?

As I thought about the machine, it occurred to me—this isn’t rocket science. I can do this. I’ll make my own!

The first order of business was addressing the question of temperature stability. From experts to serious hobbyists, everyone seemed to agree that controlling the brew temperature was the name of the game. But as I researched further, I found it wasn't easy to quantify. Should I build a thermosyphon like an E61? Or a saturated group like La Marzocco? The list of possibilities went on.

In the end, I decided to use an E61 group as the heart of my espresso machine, but with an added twist that I’ll explain shortly. Since it’s too much work to machine a one-off grouphead, I acquired a stock E61 from Italy as the foundation of my design. But as I said, it started out stock (insert manical, gleeful cackling).

Thanks to the combination of slow European shippers and frequent holidays in Italy, I had to wait four long months for the heavy, gleaming grouphead to arrive. Once I had it, I couldn't wait to disassemble it and figure out the inner workings. Then came the tedious job of measuring each piece and putting it in the CAD system... about 50 hours later, it was digital! Then came the tweaks. Acquiring metric fittings in the U.S. to match the grouphead water inlets wasn’t easy. In fact, even identifying them wasn’t easy. So instead I chose to eliminate the inlet fittings completely by drilling out the entry hole and adding a “trunk” to join the boiler and grouphead directly (shown in blue in the diagram above).

Here’s what came together:

• Espresso only. I didn’t need steamed milk—plus the ability to steam adds a great deal of complexity to the design and fabrication.
• 1.7 liter brew boiler made of stainless steel.
• 1500 Watt heating element.
• Modified E61 grouphead to become an integral extension of the boiler. Similar to the design popularized by La Marzocco, it is known as a saturated group. There is no need for a thermosyphon loop.
• Electronic “bang-bang” temperature sensor controlling a solid state relay, which in turn powers the heating element. This type of control system is electrically equivalent to a conventional thermostat, with one important exception: There is no deadband. That is, the set temperature is the point at which the element turns both on and off. If a conventional thermostat turns on, at say 195°F and off at 205°F, the hysteresis, or deadband, is 10°F. A consequence of a “bang-bang” is that it may “chatter” at the set temperature, turning on and off erratically. This is why most systems allow for some hysteresis to avoid chatter that could otherwise damage the switches. Hence the use of a solid state relay (SSR), which can react instantaneously without wearing out. In my set-up, it turns out that there is a small physical hysteresis in the system itself, so there is some minor on/off cycling of the SSR. The delay between the on/off is due to the lag as heat conducts from the element to the sensor.
• 52W ULKA vibration pump.
• Copper tube wrap around boiler to preheat brew water before entry into the boiler.
• Grouphead anchored to boiler, not the front panel, to eliminate any wiggle when locking in the portafilter.
• Separate heating element under cup warmer to actively warm them.
• Brew temp adjustable from 90-99°C.
• One-liter drip tray.
• All stainless-steel body.
• Adjustable pump pressure regulator.
• Operates on a 15A circuit.

Engineer’s Corner

I’ve read some discussions about the heat capacities of water and brass stating brass has roughly 1/10th the heat capacity of water, and so is relatively insignificant. It should be noted, however, that heat capacity is measured in Joules per gram degrees Centigrade. The per gram part is important. Specifically the density of brass is about 8.5 times that of water, so by volume, the heat capacities of the two substances are much closer.

The machine worked well. So well in fact, that I gave it to my father. Now that I had done it once I could always make another!

With thermogrease on the temperature sensor in the boiler’s thermo well, the boiler temperature remained steady within 2°C. I didn't have the necessary equipment to measure the brew temperature in the basket during an extraction, but I expect it was even steadier at the puck after passing through the large mass of the grouphead.

Well now I’m working on the next one, but it’s still in the early stages.

It began at an innocent get-together over espresso...

Later while surfing CoffeeGeek, I noticed an EspressoFest announcement—I was surprised to read it was happening only minutes from where I work! Later I learned there was an active local coffee community in the North Carolina Triad that met weekly at the same location. Getting together with my fellow enthusiasts quickly became a weekly habit; you can read about our discussions and experiments in the thread Friday Espresso Lab at Counter Culture Coffee.

During one of our espresso labs, the craze about “bottomless portafilters” came up. When I heard they were done with a hole saw, I thought that I could do it more elegantly. So I cut a couple for a few friends using a milling machine, and now look where that got me...

The La Spaziale S1 portafilter and its jig on the rotary table. The table and portafilter rotate around the center of the spout. The large spinning tool is stationary.		The S1 and Rancilio portafilters, bottomless. Aren’t they scandalous?

A batch of Rancilios at the finished straight-cut stage. Awaiting the radius cut.		Here are some of the centers of the portafilters (for sale—cheap!), plus some shavings generated in the process.

You can see these in action in the how-to article Perfecting the Naked Extraction. To give you an idea of what’s involved in machining one of the above portafilters, I've outlined the steps in the next section.

Bottomless portafilter fabrication steps

The machining is done on a small conventional milling machine fitted with a rotary table as follows:

• Build a jig that holds the portafilter precisely in place using the portafilter’s bayonet tabs. The jig looks essentially like an upside-down grouphead.
• Mount the jig on the rotary table so that the portafilter’s spout hole is centered precisely.
• Center the rotary table on the machine so that the center of the spindle is aligned with the rotary axis.
• Offset the rotary table, using the machine table, by the radius of the hole being made (minus the cutting tool’s radius).
• Turn on the mill and lower the cutting tool through the portafilter, then rotate the table. This creates a circular tool path and cuts the center of the portafilter out. This is known as the roughing pass. Move the table out a few thousandths of an inch (usually ten in my case) and “go ’round again.” This is the finish pass.
• Raise and remove the cutting tool and replace it with the radius tool. Lower the radius tool until proper tangency is achieved, and rotate the table. Now the part is radiused too.
• Raise the radius tool, change portafilters and start over...

On some portafilters, such as the S1 pictured above, the handle joint of the casting crosses the perimeter of the hole. In that case, the radius tool must be started and stopped at the right position so that it does not cut into the handle joint.

Closing trivia

My rotary table is geared such that 90 turns of the hand crank amounts to one rotation of the table. A little math, and you’ll discover that in a batch of 50 portafilters, I turn that crank about 13,500 times.

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