Thank you FotonDrv. Indeed, we shall see whether or not I can pull this off! Technically, I am certain that it is viable. Economically, its a different story. It is one thing to build a single machine from off-the-shelf parts. Its entirely another to have castings and parts made. Economies of scale become significant. A great deal depends on things that are out of my direct control - the foundry being the earliest example.

bidoowee wrote:Hi dominico

Lol - While the Bernoulli equation can be used to calculate the aerodynamic lift of an airfoil it has more important applications in the study of the fluid dynamics of coffee! This is especially true at Nasa, which makes a lot of sense if you think about it as I bet they drink a lot of coffee.

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I agree that the flow restriction caused by the puck will have some effect on the pressure, however, because the fluid velocity is so low, I suspect that the dynamic pressure component in the system is very small compared to the static part. Thus changes that affect the flow velocity (tamp, grind etc) are likely to have a negligible impact.

The trapped air pocket is an interesting thought. Do you not think that the air in the chamber would be expelled through the puck by the pressure from the service line ?

Here is a post from a few months ago where I built a portafilter pressure gauge with needle valve to simulate puck resistance.
Pressure Profiling Techniques for Spring Levers
The max pressure does change depending on what you set the flow rate to be, albeit as you say by a rather small amount if you keep the setting within the generally desired espresso flow zone.

The main issue with the air pocket is that it causes the "catch point" of the piston when you release the lever to be lower, thus a lower max pressure with a bigger air pocket. This is easily observable with the pressure gauge. The higher the lever catch angle the lower the overall pressure.

bidoowee wrote: As for changing the pressure profile by lending the spring a hand (rendering your lever "semi-manual") - there you have me. I don't know that much about manual lever machines, are there many out there with a pressure gauge for monitoring the pull?

The two I know of which sport brew chamber pressure gauges are (which aren't technically "levers" but are piston espresso machines at least) are the Rossa and the EspressoForge.

Anyway, all I'm really trying to say is that it might be a popular feature.

bidoowee wrote:From the pressure gauge and detailing of the trim around the warming tray, it looks like one of the Europa versions. Do you have any pictures of the inside?

I've thought a bit about adding cartridge heaters to the group, but I haven't come to any conclusions yet. Not only would it bring the group up to temperature more quickly, it would also allow finer control of group set point itself with a PID loop. The question for me is where to put them?

Agreed with you completely on the approach to cartridge heater - I want them tucked away too. On a stock Brugnetti Aurora's group head, indeed there's very little space for addition of cartidge heater. I was thinking more along the line that - since you're in the process of 'shaping' the group head, might as well add more meat to the group so you can drill a slot or two later on.

I am not sure if it's a Europa version or how many version are there. There isn't a official naming on my machine other than 'Aurora'. I have some pictures in the thread I posted in 'New' lever in the house!! - Brugnetti Aurora Single Group

This picture posted by Vicroamer on another coffee forum shows the internal and hydraulic well - it is similar to my Aurora. Looks simple enough to replicate. Yup, you're right - just element and pstat for electric/electronic - oh, and the pilot lamp too.

Here is a post from a few months ago where I built a portafilter pressure gauge

dominico - Indeed, I should have said piston, not lever. Is there a link to go with that? I'm intrigued. The Rossa and the EspressoForge are both super. Given that it is simple to add a threaded hole through the side of the neck and either cap it or plumb in a pressure gauge, I will certainly do this to the functional prototype of the group body when I receive it from the foundry.

samuel - Thanks for those links that is useful information. Yours is a horseshoe HX with the hand-made flanged boiler. I'm pretty sure that those are the Termazona models. With regards to the cartridge heater, yes, it would be possible to add more meat, but I'm am not keen on radically altering the aesthetic of the group. One possible placement would be at the back of the cylindrical section on both sides of the junction of the neck. Sort of like a pair of vertical torpedo tubes... In any case, I am inclined to do some testing first to see how the machine performs with significantly finer control of the boiler.

Cool project! I've always liked the look of that machine and they don't seem to come up for sale very often either.

bidoowee wrote:dominico - Indeed, I should have said piston, not lever. Is there a link to go with that? I'm intrigued.

I edited the post right after posting it to include the link but you must have seen it before my edit.
I'll post it again: Pressure Profiling Techniques for Spring Levers

Speaking of the foundry: here it is! The square block at the top is the riser which provides a reservoir of molten metal that is drawn into the casting as it solidifies and shrinks. There seems to be a few slight dents in the cast, likely the wax pattern was dinged before it was put into the investment. They should come out in the polishing, though are couple are pretty deep. Now it is off to for machining.



This leads me to a discussion of the material. This is a functional prototype made from a brass alloy similar to C69400, which is not an ideal material for a couple of reasons. The first is that the lead content likely exceeds allowable levels (0.3% in the US). The second is that C69400 has no additives to prevent (or rather retard) dezincification, the process whereby the zinc is stripped from the metal leaving a weak and brittle copper sponge which can ultimately lead to failure of a part at pressure. Dezincification resistance is especially important for espresso machines because of the operating temperature, the acidity of coffee and often, due to the use of water softeners, the mild salinity of the water itself.

From the excellent copper.org website:

Sand-cast faucets and other plumbing components have traditionally been made from leaded red, semi-red and yellow brasses. The most common plumbing brass, C84400 (also known as 81 Metal or 81-3-7-9) contains nominally 7% lead. The most popular red brass, C83600 (85 Metal, 85-5-5-5), contains nominally 5% lead. Permanent mold and pressure die castings of plumbing components are also commonly made of the leaded yellow brass alloy C85800, which contains nominally 1.5% lead.

Lead is added to brass to improve machinability. It acts as a lubricant and causes the chips to break into small pieces while it is being cut. Worse still, because of the way the lead crystals form as the liquid metal solidifies in the mold, the concentration of lead is highest at the inside surface - i.e. where it comes into contact with the water. The unfortunate conclusion is that it is highly likely that both my machines (and indeed all vintage espresso machines), help me meet my recommended daily dose of lead in the morning. This was just the way things were was until California passed its law in 2006. Since then, considerable effort has been made to find alternatives to leaded brass.

Try insulate the grouper with fabric and clad those fabric , something like this http://www.cwginsulation.com.au/images/ ... re-294.jpg ?

The prototype of the group body is done. Although there are a few minor surface blemishes, the overall finish looks to be on par or better than the two vintage groups that I have. Certainly, the lines are a little crisper. A closer inspection of the photos indicates that there may be an issue or two to address with the secondary machining processes. I've requested a few more photos and some QC measurements. There part may have to go back for a little more machining before it is shipped.

bidoowee wrote: I don't know that much about manual lever machines, are there many out there with a pressure gauge for monitoring the pull?

I don't think there are many, but it's interesting to see that some impòrtant manufacturers sell some artifacts to do that task, as this Carimali 700113CA filter holder with gauge...

http://www.espresso-solutions.co.uk/page/carimali/03/