Introduction: How to Make a Lever Espresso Coffee Machine
The espresso machine was first patented in 1884 by Angelo Moriondo but, at the time, the main incentive for such an invention was simply to speed up the coffee brewing process. It wasn’t until the mid 1900s that the espresso became what we know of as espresso today.
Fundamentally, the espresso is characterised by the brewing method; hot, pressurised water pushed through finely ground coffee causes the soluble material within the ground coffee to dissolve in the water, forming the coffee that we drink. In principle, the process is simple. In practice, there are several variables that we need to simultaneously control: the main ones being water temperature, water pressure, water flow rate, brew time, type of bean, roast of bean, grind size and grind quantity. These variables can be characterised into two groups: relating to the water and relating to the coffee. The grinder is typically used to control the variables relating to the coffee, whereas the espresso machine itself controls the variables relating to the water.
In this instructable, I will take you through the design and manufacturing steps required to make a simple lever espresso machine to control the water flow rate and pressure through ground coffee and ultimately make delicious espressos.
- Handle (19 mm OD, 16 mm ID stainless steel tube)
- Con rod (16 mm diameter stainless steel 303)
- Con rod bushings (10 mm OD brass or bronze)
- Lever joint (3/4 inch or 20 mm square brass bar)
- Lever pins (8 mm diameter stainless steel 303)
- Pivot block (2 inch or 50 mm brass bar, or can be fabricated from two pieces)
- Piston (1 ¾ inch or 45 mm brass bar)
- Gudgeon pin (14 mm diameter stainless steel 303. Can be machined from 16, as used for the con rod)
- Gudgeon pin washer (14 mm diameter stainless steel 303. Can be machined from 16, as used for the con rod)
- Cylinder (2 ¾ inch or 70 mm diameter aluminium or brass bar)
- Cylinder liner (2 3/8 inch or 60 mm acetal (Delrin) bar)
- Valve piston (1 inch or 25 mm brass bar)
- Stand & base (approximately 30 mm thick hardwood such as mahogany or oak)
- Piston O-rings (42 mm OD by 3 mm thick)
- Valve O-ring (18 mm OD by 2.5 mm thick)
- Gudgeon pin circlip (stainless steel for 8 mm shaft)
- Tamper (step 18)
- Coffee grinder
- Knock box (optional)
- Drip tray (optional)
Step 1: Design
The main components of the machine are the cylinder, piston (with an inbuilt one-way valve) and lever. The lever provides the mechanical advantage required to generate the required pressure within the cylinder. Most commercial machines are calibrated to operate at 9 bar pressure, so this is the target pressure. The pressure can be easily calculated from the mechanical advantage provided by the lever and the piston area. The area of the piston is also determined by the volume of espresso desired, as is the piston stroke and therefore cylinder length. The piston stroke is a function of the minor lever length, which effects the mechanical advantage. All of this can be modelled with simple equations, as shown in the attached document. I have done my best to optimise the design based on my preferences but please do try out changing design aspects to meet your personal preferences.
Although I was trying to keep the design of the machine as simple as possible, I felt it was necessary to include a one-way valve in the piston. This allows water to flow through the piston when the lever is lifted but pressurise the water when the lever is pushed down. This enables the user to fill the cylinder with hot water without completely removing and reinserting the piston into the cylinder before the water goes cold: not something you want to be doing before your morning coffee! When the lever is lifted, a small piston inside the main piston moves upwards slightly which opens a pathway for water to run through the piston assembly. When the lever is pushed down, the small piston seals against the inside face of the main piston.
The prototype cylinder was initially made from one piece of aluminium. However, due to the thermal conductivity of the material, the water wouldn’t maintain its heat when brewing, unless the whole cylinder was heated beforehand. The final cylinder hence incorporated an acetal liner which insulated the hot water from the main body of the cylinder. (The thermal conductivity of acetal is approximately 700 times smaller than the thermal conductivity of aluminium.)
Several prototype designs were manufactured and are shown in the images - including disasters! A picture of my dad's version is also shown (last image). Rest assured that the final version has been making two espressos per day for the last few months with no explosions!
Step 2: Cylinder
This is the hardest component to manufacture, partly due to its size (it is likely towards the upper end of machining capability on many hobby lathes) and partly due to the portafilter attachment. It is also possible to make a screw-on portafilter instead of using a commercial one and screw cutting the cylinder to fit.
The cylinder is first bored to size. This dimension is not too critical because the plastic liner can be later machined to fit. The recess can be machined to a slightly larger diameter than the body of the portafilter. For the new La Pavoni portafilter, the recess can be machined to 60.5 mm in diameter (the body of the portafilter is 60.0 mm in diameter). Do bear in mind that the shower screen and gasket needs to be a snug fit into this recess; this may require a small taper or step down in diameter. The groove to accept the portafilter tangs can then be machined. The cylinder can be mounted to a rotary table in the milling machine to make the notches for the portafilter tangs to slot in to. Use a Dremel to grind a short lead-in to make slotting the portafilter into place easier. A gravograph engraver was used to engrave the lock symbol onto the cylinder. The engraving is not essential but is very useful to help align the portafilter so it is recommended to apply some sort of mark.
Three holes can be drilled and tapped M6 in the side. Ideally, they should be blind, but it is not essential.
Step 3: Cylinder Liner
The cylinder liner needs to be made from a thermal insulator – Acetal (AKA Delrin) is an excellent material for this and is lovely to machine. The internal finish needs to be as good as possible and the bore needs to be parallel apart from a small internal chamfer at the top to guide the piston in when fitting. The liner should be a tight fit in the cylinder. The thickness of the flange is critical because it determines how tight the portafilter is and therefore ensures a good seal between the portafilter and cylinder. This will involve fitting the shower screen and gasket (most likely multiple times) to test the fit. The flange thickness can be made oversize, fitted to the cylinder and then machined while attached to the cylinder. If machined too far, the liner can be removed, and a shim can be fitted behind the flange before reinserting it into the cylinder. If using the La Pavoni gasket, an internal radius should be machined to match the gasket. The shower screen should be a tight fit to prevent it falling out during use.
From here on, the cylinder and cylinder liner subassembly will be referred to as the cylinder.
Step 4: Piston
The piston can be made from brass or stainless steel. The O-ring grooves should be left oversize and tested for fit in the cylinder before machining to final size. The upper groove is less critical so should be machined first. The internal hole should be bored to 25.00 mm and should have a good surface finish. The bottom of the internal cavity should be flat and also have a good surface finish because the valve piston will need to seal on this face. The hole in the bottom isn’t critical but was drilled to 8 mm diameter. This hole will allow water to flow through the piston when the handle is lifted. The internal chamfer at the top of the piston is for aesthetic purposes and to reduce the thermal mass of the piston – it is not required for con-rod clearance. Small external chamfers or fillets on the top and bottom reduces the risk of the piston scratching the inside of the cylinder when it is being fitted and removed. With no O-rings fitted, a 0.2 mm diametrical clearance between the piston and cylinder is advised so no rubbing occurs during use; this clearance also accounts for thermal expansion. The aim is for just the O-rings to contact the inside surface of the cylinder.
A mandrel was machined from square aluminium bar to fit snugly into the internal hole in the piston. The end of the mandrel was drilled and tapped M8 so the piston could be bolted securely to it. The mandrel and piston were mounted horizontally in the milling machine so the slots and flats could be milled. If the mandrel was machined concentrically, it can be flipped by 180 degrees to mill the opposite side without needing to set the piston back up again.
Step 5: Valve Piston
The valve piston is the small piston that slides inside the main piston. When the handle is pushed down, the bottom of the valve piston seals against the inside face of the main piston, allowing the water to be pressurised. When the handle is lifted, the valve piston moves upwards, which allows water to flow through the hole in the bottom of the main piston, around the smaller diameter part of the valve piston and then through the valve piston con-rod slot. A movement of just a few millimetres is enough for this to be effective.
The valve piston should be machined to a diameter of 24.90-24.95 mm while still attached to the bar. The groove should be machined while the workpiece is still attached to the bar stock. The hole for the gudgeon pin needs to be drilled and reamed accurately perpendicular to the slot. Only then can it be sawn or parted off and carefully held in a 4 jaw chuck for the finishing operations on the other end – the groove can be cut and the end machined to a smaller diameter to allow water to flow through. The groove in the bottom of the valve piston holds an O-ring to help the valve piston seal. A small angle on the inside of the groove helps hold the O-ring in place (see diagram).
Step 6: Con-rod
The con-rod is made from stainless steel and can be shaped according to your preference. The con-rod could be left at 16 mm diameter; however, material removal is advised to increase the available volume and to reduce the amount of metal that needs heating during brewing. The holes require bushings made from brass or bronze to prevent galling with the pivot pin and the gudgeon pin. The flats are simply milled in a milling machine or using the vertical slide on the lathe cross slide and then cleaned up with a file.
Step 7: Gudgeon Pin
This is a straight-forward machining task. The circlip groove should be machined according to the circlip dimensions. The pin should be carefully turned to the correct dimension.
Step 8: Gudgeon Pin Washer
This is an optional component: it is simply a washer that sits between the circlip and piston. Ideally, a custom washer is machined, and the back face is polished to reduce friction but a standard M8 washer will work, provided it is made from stainless steel.
Step 9: Lever Joint
This component allows the handle to be attached and connects the con-rod to the back board. The slot for the con rod can be milled as a straight-walled through hole but it does look neater if made blind. The hole contacts the con-rod at the extreme angles (±45°) so acts as a stop to prevent the piston popping out the top of the cylinder or pushing the shower screen out the bottom. Therefore, the hole needs to be the correct dimension and the angled sides allow a large contact area with the cod-rod at these limits. The con-rod pivot should be drilled and reamed 8 mm on one side and tapped M8 on the other. The other pivot should be drilled and reamed 8 mm. The curved recesses on each side around the main pivot hole can be turned on the lathe by mounting the block to a faceplate.
Step 10: Handle
There is a lot of potential design freedom with the handle. It could be a rod which screws into the lever joint, it could be made from wood, or it could be a tube that slots onto a boss machined onto the lever joint (my chosen method).
Step 11: Pivot Block
The pivot block attaches the lever joint to the back board. The part can be shaped as desired. The main thing to be aware of is to ensure the hole is exactly perpendicular to the slot. The hole is plain 8 mm diameter on one side and tapped M8 on the other, much like the con-rod pivot hole in the lever joint. This part could be machined from solid or fabricated from two parts.
Step 12: Pivot Pins
The pivot pins are most easily made by cutting an M8 thread onto the end of a length of 8 mm stainless steel, held in a collet. The thread is best formed by screw cutting in the lathe, but a die may also be used. After cutting and facing to length, the slot can be formed with a hacksaw, a knife file or a slitting saw. Clickspring has a video demonstrating how to align the screw slots https://www.youtube.com/watch?v=QxJZdQk-MBg
Step 13: Back Block
This part is required to fit the cylinder to the stand. It can be machined from metal, wood or nylon. If metal is used, it is best to match the material used for the cylinder to avoid galvanic corrosion of either the cylinder or the block.
One side is flat and the other is radiused to fit against the cylinder. The radius is best machined by mounting it on a vertical slide which is attached to the lathe cross slide. A boring bar can be mounted between centres and the cutter adjusted so it cuts a scoop of the same radius as the outside of the cylinder.
Step 14: Stand
The stand should be designed based on personal preference and available materials. I chose a dark hardwood for mine, but it could also be made from metal. If using wood, the backboard should be at least 30 mm thick to ensure adequate stiffness. The back board needs to be strongly joined to the base – a dovetail joint is highly recommended. A recess for the pivot block can be made with a router or on the milling machine.
You may choose to machine a recess in the base to take a drip tray – I just use a shallow tray that sits on the surface.
Once the cylinder mounting holes have been drilled and the back block has been glued to the back board, a few coats of varnish can be applied to finish. Rubber feet can be fitted to the bottom to stop the machine from moving on the worksurface when in use.
Step 15: Cylinder Securing Nuts
Due to the short lengths of thread in the side of the cylinder, it is best to make sure the studding is screwed in all the way into the cylinder. Therefore, to fix the cylinder in place, a nut is required on the other end of the studding (i.e. long bolts are not suitable because thread engagement in the cylinder won't be maximised). The easiest way to do this is with penny washers and nuts, as shown in the CAD model and the first picture. The best way to do it is to machine special blind nuts with a screwdriver slot (much like the ones used for hand saw handles), as shown in images 2 and 3.
Step 16: Assembly
The final assembly should be straight-forward; however, be prepared to make some small adjustments to some components to enable the system to work smoothly.
Before assembly, give the components a thorough clean. A smearing of machine oil or grease can be applied to the two pivot pins but use a food-safe lubrication for the gudgeon pin and piston O-rings: olive oil, lard or butter are all good options. I suspect that the lubrication on these components gets washed off after a few uses, so this is mainly to aid assembly. If there is a slight misalignment in the linkage mechanism on assembly, it might feel stiff. Ideally, the valve piston should move freely in the main piston; if it doesn’t, try skimming down the outside of the valve piston. When fitting the pivot block, take extra care to make sure the slot is vertical – the same goes for the cylinder. When the handle is lifted all the way, the top of the piston should align with the top of the cylinder. A small amount of side-to-side play on the handle is expected. Make sure the piston body isn’t rubbing on the inside of the cylinder when the handle is moved up and down – you should be able to hear a scraping noise if it is. If it is scraping, mount the piston back on the mandrel and remove a small amount off the diameter.
Step 17: Tamper
A tamper can of course be bought but if you have gotten this far in the project, you will be able to make one. This is a simple turning job and can be machined from bar stock or from thick plate. A piece of studding screwed into the tamper base works well for attaching the handle. Ideally, the handle should be made from the same wood used for the stand. The tamping face can be any desired shape but the most popular choices are either flat or slightly convex.
Step 18: Make and Enjoy Your First Espresso!
The process of making an espresso with this machine is very similar to any other lever espresso machine. You will need a good quality grinder so you can properly dial-in your grind size. Always make sure you preheat the machine and your cup by filling with boiling water at least once. If you are using a portafilter with a spout, that will also need preheating (not necessary if using a bottomless portafilter). Aim for a 30 second extraction time with 15-20 kg of force on the handle (see calcs from the design stage). Make sure you lift the handle to release the pressure before removing the portafilter. Enjoy!
I would like to acknowledge Hazel Mitchell and my father, Alastair Godfrey for his considerable help with the design and manufacture of the machine.
First Prize in the
Coffee Speed Challenge