Hi, there!

Finally I've got the additional spring to Mini Gaggia. I've done some calculation and talked to the spring shop, so the final product is 96mm long, has 27mm external diameter, 20mm internal diameter, 3.5mm wire, 11.5 total coils made of AISI 302 SS:



And installed:



They tested it and the spring rate is 1,125 kgf/mm. So it should add around 2 bar (38 kgf) when the piston seal the chamber (considering 18.8 mm² of area), as the spring installed has 82mm and when sealing the chamber has around 62mm. Most important is the coffee - I've done some tests with the Gaggia Achille filter basket and using the same 18g and finely ground coffee the spring did a similar job on Mini Gaggia that my arms on Achille (I hardly can reach 8 bar, measured with a gauge on the porta-filter).

The lever is heavier now, for sure, but a normal size man or woman can pull it. I'm using the porta-filter to counter balance. Maybe a 8-10cm addition to the lever could help a little bit, but with less balance - perhaps it would require the other hand to hold the machine base or back.

The machine support and screws don't seem to care about the extra force.

Note to anyone that would remove the piston (unscrew it): hold the spring at the current length with cable-ties (a lot). I've used 3.5mm wide cable-ties, maybe 4-5 around each coil, to hold the spring at a enough length so I could screw the piston back to the shaft.

I have 12 more springs, I think 6 or 7 of them are going to Europe to a fellow HB member that could send the spring to other Mini Gaggia owners. If anybody is willing to take 5-6 at North America, I could send them. The cost of each spring is 7.5 USD.

Márcio.

Machine done! Plastic body painted in red (I have an extra, the original cream is intact), double spring, stainless steel panels polished, silicon sealing the boiler, a very small hole at the side of the machine to set the bimetallic thermostat:



Well, crappy picture... I'll make a video from the extraction with the double spring tomorrow.

Márcio.

Here are the movies. First one, 15g (Virtuoso Preciso, macro 9, micro F). Second one, 14g, two micros up (H). The first grind setting was giving me a ristretto shot on Oscar, using 16g, same coffee (9 days post roast).





I would make a third shot, using the first grind with 15g to help the lever a little bit but the Preciso died - the inner burr is jammed to espresso grind, I'll have to take a look...

Márcio.

Wonderful!

More videos. I was not paying attention to basket preparation at all, so the extractions are bad. Just to see some Mini Gaggia porn:

Water spray:



Three shots. First bad, second not so bad, and the third at another angle...







And just for a poor comparison, on Achille using the same filter basket from Mini Gaggia. For me, to reach 8 bar on the Achille is hard. The camera was partially on the base of the machine so the trembling is me struggling to pull the shot.



This Mini Gaggia filter basket is for double (it can take 16g) but is very tapered. Seems harder to use than the traditional ones, for instance the Achille's double basket.

BTW, the 3 shots from the Mini was very nice, I wonder if I take more care or use a better (or easier) basket!

I've done some Scace reading (but my digital thermometer is not a Fluke), comparing the temp of boiler water, measured with a digital probe (it says 1°C accuracy), and I get, in general, 0.7°C-0.9°C less at the filter basket, but a very flat profile. If I let the water reach 97°C for some seconds, then wait for a target temperature, then the difference is very small, less than 0.5°C.

The only conclusion I could reach is that at the peak temperature of the water after the thermostat switches off (for instance I've set it so the water reaches a maximum 95°C) the difference is at least 1°C. After some seconds the metal and water are at balance and the shot will be very close to what you read at a water temp probe (considering it's calibrated, of course). Kind of obvious, I know...

Márcio.

Carneiro wrote:Machine done! Plastic body painted in red (I have an extra, the original cream is intact), double spring, stainless steel panels polished, silicon sealing the boiler, a very small hole at the side of the machine to set the bimetallic thermostat:

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Well, crappy picture... I'll make a video from the extraction with the double spring tomorrow.

Márcio.

I noticed that in your picture your outlet has ground on both sides so you can put the plug either way.. never saw that before!

No, that was the crappy standard in Brazil until now. The power outlets was like this, to use rounded or flat plugs, but now ground! Then people used to install ground at specific outlets for refrigerator and other high power appliances.

There is a 220V outlet at my kitchen with the American stantard, I've installed a power cord from a computer at the Mini Gaggia.

Now the stantard is a very similar one to the Swiss power outlet.

Márcio.

As Márcio already mentioned, six springs made their way to a fellow HB member in Europe. Said HB'er being yours truly. So, pm me, if you're interested and want a spring.

This weekend I found some time to work on the Mini Gaggia. And some time is all you need; adding the spring is almost a no-brainer, and takes half an hour - tops.
With the second spring in position, pulling down the lever obviously requires more force. I was a bit anxious about the frame flexing as a result, but noticed none while checking movement before putting the machine back in its shell.

I've no Scace pf or other gear to measure the pressure during a pull, but I'll take Márcio's word on that. What I can say is that the second spring has significantly improved mouthfeel and aftertaste of the Mini G's shots. The shots have gone up from ok-ish coffee to pretty decent espresso. I think that's certainly worth the effort.

I've posted some pix of the mod and a vid of one of the first shots. Will post more vids of better shots if/when I've time.

Cheers,

- hv

Thanks to Carneiro, a handful of the custom springs he had manufactured for his Mini rebuild have arrived here in the US.

I plan to start my own rebuild project shortly, but anyone interested in a spring should PM me and I would be glad to hook you up at cost plus shipping...