Do you know if the condition is due to the quality of the solder or simply standard for soldered connections? I'm curious how long new soldered connections last on current machines.

Regards,
T.

I wonder how you decide the shape and material used for the new springs... is it completely random, made by feeling/experience or calculations (considering the piston area and Pascal's law) ? Since this really drives the quality of the final result in the cup and considering the huge effort you put on this restoration, I'm surprised to read something like "It will be interesting to see what pressure they produce as this was a total guesstimate". How will you tweak this parameter if it's completely out of spec ?

dsc wrote:Do you know if the condition is due to the quality of the solder or simply standard for soldered connections? I'm curious how long new soldered connections last on current machines.

Regards,
T.

In a few places the lead has peeled away, it's still pretty strong though. On the whole it is still tightly bonded to the brass and copper so it will have to be melted away. I will investigate further why it has debonded though, maybe limescale??

pootoogoo wrote:I wonder how you decide the shape and material used for the new springs... is it completely random, made by feeling/experience or calculations (considering the piston area and Pascal's law) ? Since this really drives the quality of the final result in the cup and considering the huge effort you put on this restoration, I'm surprised to read something like "It will be interesting to see what pressure they produce as this was a total guesstimate". How will you tweak this parameter if it's completely out of spec ?

Yes good point, it's more an educated guess. The spring diameter is pre-determined by the OD of the piston (45mm to 49mm depending upon which machine you are working on), all lever springs use pretty much the same gauge wire (approx 7mm), and the same height 140-150mm (the new levers are a bit longer though), and they all have roughly the same number of coils 9-11. The only unknown will be the overall height which can be calculated by measuring the pitch, or the gap between coils of the existing spring. I take the largest gap I can find on the spring (since they have been squashed over the years) assume that was how it was when it was new and then use that as the pitch for all coils in the new spring. And voila you end up with your height measurement. It's a tried and tested method.

The only major mistake you can make with springs is with the number of coils. If you have the right length but too many coils and the spring will not compress as the coils touch. Also if you have the right number of coils but too long in length it will also bottom out before the lever is fully down.

The springs are fairly basic technology, the old levers brew at the group anywhere from 5-8 bar. I've never found a new official spring to produce more than 8 at the group. If you hit anywhere between 5 and 8 you have a good old fashioned lever machine, it's more about the flow and saturation of the coffee. The 9 bars comes from pump machines and should be applied to those machines.

So I don't think there is a "spec" for these machines, there is a range. And you would have to make a huge mistake (say 3mm wire instead of 7mm) for it to be out of the expected range.

Paul_Pratt wrote: I've never found a new official spring to produce more than 8 at the group. If you hit anywhere between 5 and 8 you have a good old fashioned lever machine, it's more about the flow and saturation of the coffee. The 9 bars comes from pump machines and should be applied to those machines.

Thanks for this, Paul. That's a useful data point from someone who specs springs for many classic commercial levers. The Bezzera Strega hybrid design now makes even more sense (using a pump capable of higher pressure and mostly for pre-infusion).

Then I'll have it silver soldered to make it watertight. More next week.

Look forward to seeing this. It's a large piece.

I have not done anything for weeks now, but I did spend an hour this afternoon investigating the lead solder on the boiler. I can confirm that it has lifted in places due to limescale creeping under the joints. Obviously in order to have the boiler soldered back up properly I will have to have to get rid of the limescale.

I don't think citric will touch it. I have not used HCL for years so I will try and find some.

Great work as usual!

You might be able to find HCl in the hardware store under 'brick' cleaner. Hope this helps.

Cheers

Common name is muriatic acid and pool chemical supply or most ACE Hardware stores have it on the shelf. Do not store inside of a dwelling or other building as the HCL gas will slowly permeate the container and cause iron/steel to rust and chrome plate to fog.

I store mine on the shady side of an shed outside under a larger plastic bucket and it keeps real well with no issues.

Americans really don't understand the Hong Kong environment Paul works in. The only traditional "big box" store I can think of is Ikea, all the rest are tiny shophouses. I'd bet there are 20 places selling HCl within walking distance of Paul's factory.

Hydrochloric acid is commonly used by Italian machine manufacturers for service and restoration work, but the guys using it are dressed in big, hard plastic aprons, shoulder length rubber gloves and full face transparent "welding" masks. I wouldn't attempt it without similar protection.

Alan

Alan Frew wrote:Americans really don't understand the Hong Kong environment Paul works in. The only traditional "big box" store I can think of is Ikea, all the rest are tiny shophouses. I'd bet there are 20 places selling HCl within walking distance of Paul's factory.

It's changing fast, mostly office space these days.

Hydrochloric acid is commonly used by Italian machine manufacturers for service and restoration work, but the guys using it are dressed in big, hard plastic aprons, shoulder length rubber gloves and full face transparent "welding" masks. I wouldn't attempt it without similar protection.

Alan

Yes that's why I stopped using it before. Really nasty stuff. I'll think on it some more, too busy at the moment to do any work on it anyway.