Pocket Size Espresso Machine With Integrated Alcohol Stove.

Introduction

I’ve always been fascinated by small things. I remember going to the mall as a kid and seeing all the Hello Kitty mini stuff at Spencers, and being really disappointed that they only made girl stuff (it was years later before they came out with boy stuff)
So, when the Pocket Size contest was announced, it really inspired me to design and build something new.

“Mmmmm Ok, now what?” I said to myself.

So I started browsing Instructables, trying to find some inspiration when I remembered that the year before, my Espresso machine had died, and I had played around with the idea of building one.

I looked at all the Instructables relating to coffee at the time, but no one had built a machine. The quest ended that Christmas with the gift from my wife – a new espresso machine (I know, she’s really great :D ).

This year, a quick search showed that there were still no Instructables on how to build an Espresso machine….and inspiration came: I would build a pocket sized Espresso Machine.

Now, I’m going to stray a bit from the normal Instructable format and include two sections: Design and Build.

One reason to do this is because I’ve noticed a number of kids on the site, and maybe, just maybe, reading about the design process might inspire them to build great stuff.

Another is that, because it had to be pocket size, I took some decisions that may seem odd, and telling you how I got there will help you modify this project more easily to better meet your coffee needs (like making it bigger).

Also, as it turned out, the alcohol stove that came out of this is a rather novel design, easily modified, that might breed a whole new class of alcohol stoves. :D
Three cheers to giving back to the community!!

Design constraints are some of the most important points of any product design; they tell us what the limits are. The tighter the constraints, the more limited the design, and we have to be more creative to be able to meet them.

On this project, I set the following ones.
1- The product had to fit in the pocket of my jeans.
2- The product had to be made out with common, cheap and easily obtainable materials from any home improvement store or corner hardware store.
3- The product had to be made using simple tools that most makers would probably already have, or could easily borrow or buy cheaply.
4- The product had to be self-contained.
5- The budget was maximum 30 dollars.

These five simple constraints really guided the design and build of the espresso maker, sometimes in unexpected ways.

First of, what is Espresso?
Wikipedia defines it as:
Espresso is a concentrated beverage brewed by forcing a small amount of nearly boiling water under pressure through finely ground coffee.

So, lets start writing some more constraints: 

How much water and coffee?
Again, Wikipedia tells us that:
The size can be a single, double, or triple, which corresponds roughly to a 1, 2, and 3 US fluid ounce (approximately 30, 60 or 90ml) standard (normale) shot, and use a proportional amount of ground coffee, roughly 7–8, 14–16, and 21–24 grams; correspondingly sized filter baskets are used.

How much pressure?
Wikipedia says,
There is no universal standard defining the process of extracting espresso, but there are several published definitions which attempt to place constraints on the amount and type of ground coffee used, the temperature and pressure of the water, and the rate of extraction

A quick web search tells us that the maximum pressure is nine bars, but if we have less, we could still call our coffee “an espresso”.

I took a measuring cup and a scale and measured out water and coffee for 1, 2 and 3 shots, and due to design constraint number 1, this will have to be a single shot machine, since there was no way I could fit a larger machine in my pocket.

Now that I knew the dimensions that my machine was going to have, I went looking for “the competition”.

I googled “pocket sized espresso maker”, and found only two: The Handpresso and the Mypressi Twist.
The Handpresso uses a nicer relative of a bike pump to achieve the required pressure, while the Twist uses a gas cartridge to deliver the 9 bars of pressure. But both have one thing in common: they both require you to “add hot water”. This meant that there was an external heat source that got the water up to the “near boil”, as Wikipedia told us.
But, constraint number 4 tells us that it had to be self contained, so this puts my little machine in a different category.

This led to a problem…how to get the water to the correct temperature in a self-contained machine?

The only viable option was some kind of stove. A lot of online research further narrowed it down to an alcohol stove.

Now, a little bit about myself: I’m more than a bit clumsy, so the thought of alcohol burning close to me kind of freaked me out.

So I came out with design constraint number 6: It must be safe.
This constraint turned out to be the toughest one of them all.

The Espresso Machine is divided into 3 parts: The brew head, the boiler and the stove.

So, on to the build and more design choices!

Design:
Since constraint number 2 said that the parts had to come from a local home improvement store or hardware store, off I went to Home Depot.

I knew that what I needed was copper plumbing parts, because they’re cheap and copper is soft and easy to solder.

Once I got there, I just stared at what was in front of me and figured out how to make those pieces fit into what I needed, which was a kind of tiny Kelly Kettle.
I only bought the parts I needed for the boiler, because it would define the size and general shape of the machine, and to make sure that once built, it would still fit in my pocket.

I chose the 1in sized parts as the maximum sized ones, simply because they where the largest diameter tubes that fit comfortably in my pocket.

Some makers have commented on two possible problems they see with the build:
1) Lead in the solder
2) The use of copper and food.

The first is very easy to address: just use lead-free solder.

The second one, no so easy….the main concern is that the acidity in food will rust the copper, and the resulting salts are bad for your health.
This worried me enough to call a doctor (a family friend) and asked her to look at the Instructable and to give me her medical point of view.

She said that, in general, no to worry because:
a) Copper is not toxic and we need trace amounts in our diet. As a mater of fact, there is such a thing as copper deficiency.
b) Some copper alloys are in fact antimicrobial, which is why some hospitals have copper doorknobs.
c) As in all things, an excess of copper in your body is very bad for you
d) The brewing process is short, so the possibility of corrosion will be very small.
e) If corrosion does occur, the coffee grounds will probably trap it.
f) Tinning the brew head will eliminate any possible copper corrosion.

Part list:

Pluming parts:


Screws and nuts:

For the brew head:
For the water intake hole:
For the stove:
Plastic parts:



Tool list:
Drill bits:


some small nails

Since the pictures I took sometimes don’t show very clearly what’s going on and also because a blueprint is worth 6 pages of directions, I drew one with the espresso machine cut in halve, and all the part measurements and hole sizes.

1. Drill the 4 holes into the 1 to ½in reducer
2. Ugly solder the ½ in pipe into the 1 to ½in reducer

Ugly solder?

Design constraint 3 says that only simple, cheap tools could be used. I considered that a blowtorch would not fit the bill because not everyone has one, and I would probably burn myself using one. Also, if one of the younger members wanted to make one of these as a Christmas present, I would have to find another way to solder everything together in a safer way. The only other tool that came to mind that fit the bill was a soldering iron. But nothing is free in life. It’s slow and the end product is really ugly.
I had to file the solder to make them look a bit nicer, but it was the only way to stay on the good side of the constraints.
So, I decided to call this “technique” ugly solder.

Note: Use only lead-free solder.

1. Take the ¼ in pipe and cut a V grove 1 in from one end.
2. Fold along the grove to form a 900 angle
3. Ugly solder the joint
4. With a hammer, flatten the long side of the tube.
5. Cut a small notch in the bottom of the flattened tube.

Design:

I had to flatten the tube in order for it to fit into the boiler. The notch at the bottom of the tube is just a precaution against the tube blocking during the build.

1. Like in the picture, make sure that everything fits together.
2. Ugly solder everything together (don’t forget the nut that’s parallel to the water tube)

Design:

With the boiler now finished, I had the dimensions of the stove. This was where the project would succeed or fail.

I found out that of the two kinds of small alcohol stove designs out there, the sealed ones where a bit safer. But still, if you tipped one over, you could still get alcohol lit all over the place.

And there was also the problem of the amount of fuel need. In all the designs I found you filled up the stove with fuel and used it until it ran out.

I build prototype #1 based on this concept. It was small, it ran for 20 seconds before using up its fuel and almost got me burned.

Now I knew that I needed to get more fuel into the stove, but that meant a bigger stove and that would break constraint 1. This told me that my stove had to be externally fed.
Online research only gave up 1 type of stove that fit the bill (www.minibulldesign.com/) but looking at those beautiful stoves, it was clear that they broke design constraints 2,3 and 6.

I had no option but to design a new kind of tiny, externally fed, intrinsically safe, alcohol stove.

It took me over a month of work, lots and lots of research and tinkering and refining ideas, but finally, lucky prototype number 13…..Waass aaliiiveee !!!

It ran 18 min, 36 seconds on a full charge of alcohol.
I actually had the intention of staging an “accident” where I would tip over the stove full of fuel in a controlled environment.
Luck would have it, that my clumsiness got there first: during a second run of the stove, after about a minute lit, I accidently hit it with my hand and tipped it over.  Since I was still using a piece of tape as the security cap and air flow control, all the alcohol got out and spilled over the table and on me. The stove turned off immediately after it tipped so the spilled fuel never got lit.
The design was a success!

The end design is really simple and obvious in the way good designs tend to be. The hard part was getting there.
The stove has three main parts:
1. Fuel tank with flow control
2. Vaporizer
3. Diffuser and heat exchanger.

The stove works on the principle of vaporizing only the amount of fuel to be immediately burned. This gives us two good things: it allows an external fuel source and since only a small amount of vapor is available to the flames, any interruption in fuel supply would automatically turn off the stove (constraint 6).

I made a lot of different types of flow controls (one using the valve out of a lighter) but in the end, a simple unplugged syringe with a bit of tape over the top with 1 pin sized hole in it gave me the one-drop per second that a stove this size needed. It was simple and cheap (even though they don’t sell any at Home Depot, you can get them at any pharmacy). The flow rate is so small, that the fuel tank tap only needs a tiny hole at the top to balance the pressure and keep the flow going. This also is a big win in the safety department, because the hole is in fact so small, that if you tip the fuel tank on its side, no fuel comes out.

If you want (and I can bet someone will) you can very easily scale the stove to a size big enough to use as a camp stove (there’s an idea for a future Instructable).

1. Cut and drill all the parts following the blueprint.
2. In a scrap piece of wood, drill a ¼ in hole , ½ in deep (sawing jig).
3. Place the ¼ in tube into the sawing jig and cut the 4 groves (2 at the same side, the front and back)
4. Assemble and ugly solder the fuel tube and the syringe holder
5. Place fuel tube into boiler, and ugly solder stove bottom.
6. Ugly solder the stove top
7. Once the vapor tube is in place, put the diffusion tube on top and screw in place
8. Only if needed, file the screw and nut at the bottom of the stove.

1. With patience, file the syringe needle until it breaks at the desired length. Don’t use pliers; you’ll just pinch it closed.
2. Place the syringe into its holder; it’s a tight fit.
3. Place the cap on top.

Design.

I ground 7 grams of coffee to see how much volume it took up. Then I looked over the parts that I had that could be made into the brew head. Since the boiler is really small, I decided to use another 1 to ½ in reducer as the main body of the brew head, so that I could get an espresso cup under and between it and the boiler. The reason I needed to do this was because of the small size of the machine. If I couldn’t fit the cup in there, I would have to place the espresso maker on a higher level than the cup, and that would have to be an add-on, braking constraint 4 and possibly 1.
Fortunately, everything fit great.
The last problem to overcome came from finding a way to make the metal filters that espresso makers use.
Since drilling very small holes in metal with a hand drill is rather hard, and very likely to snap the drill (and a small drill press would brake constraint 3), I had to come up with a simpler method.
A few experiments later I had the technique nailed down.


Note: Some people have expressed a bit of concern about the use of copper and food. Since the brew head is the only part of the machine that touches food (essential, life giving food :D ) you may consider:
A) Tinning the interior of the brew head and filters
B) Using a different type of metal for the brew head and filters

1. Cut and drill all the parts following the blueprint.
2. Cut open a coupler using a hacksaw and flatten the copper.
3. Hammer down the copper until it’s roughly the thickness of a needle.
4. Cut it to the size of the interior of the 1 in cap.
5. Cut another circle to the exterior size of a ½ in cap

1. Using a hammer and a nail over a scrap piece of wood make a “dimple” in the copper disk
2. Continue until you have a bunch of dimples.
3. Using sandpaper, ground out all the dimples.
4. On the dimples that left no holes behind, repeat.

1. Ugly solder the small copper filter to the 1 to ½ in reducer.
2. Ugly solder the ½ in cap to the 1 to ½ in reducer
3. Cut the water tube coming out of the boiler so that it’s flush with the 1in cap.
4. Ugly solder in place
5. Cut a ¼ in piece out of a 1 in hose gasket
6. Place in brew head top
7. Place 1 in copper filter
8. Place 1 in hose gasket to hold the filter in place.

1. Drill a 1/8 in hole through both copper filters once in place (just to make sure they’re aligned.)
2. Assemble the brew head together with the 6-32 3in screw and wingnut.

Design:
The problem came up of how to hold the brew head to the boiler body without the later popping out due to water pressure.
One thing I tried was to make the brew head out of a pair of copper hose connectors. The problem was that they were too big, it made the brew head as long as the boiler and screwing them together really tight was no easy because of the restricted grip on the piece. I then came up with the idea of using a simple screw and wingnut to hold everything together. Easy to build, easy to use and cheaper than the first alternative .

Once you’re done, wash everything and fill the espresso maker with water using the hole with the soldered nut. Place a screw in the nut with a small gasket (I used one that’s used inside some hot water faucets.)

Fill the fuel tank with alcohol and pressure place the ½ in cap.
Wait some 15 seconds for some alcohol to fill the stove.
Hold the espresso maker by the brew head and lift it. Use a lighter to heat the stove from the bottom until it ignites (takes some 10 sec.)

Place it on a flat surface and wait for the water to fill half a cup (1 oz) – takes about 3 minutes.

Wait until it cools down and repeat the process, but this time with coffee in the brew head.

Enjoy!!