The 2019 tests
I had a major problem with the stainless steam wand: it started to rust on the inside. I thought that I bought 1.4301 but actually I have no idea what type of steel it is. But as the steel is magnetic and the company who sold it was sure it is "Niro", it might just be 1.4003 - which is a ferritic chrome steel. I also found out that it machines much easier than real 1.4301, thus is not as hard, which would be the case for the nickel steel 1.4301.
Okay, so a new nozzle was the plan.
Over the time I found out that the long nozzle bore is not ideal. If something gets into the hole, you do not get it out easily. Therefore I decided that the next nozzle should have a minimal thickness in the front.
But what about the hole diamater? Judging from some threads in the german Kaffee-Netz, only the total hole area is responsible for the quality of the foam. A too large area drains the boiler too quickly, while a too small area takes much longer and the milk will get more wet. Tidaka has a very nice nozzle in their shop which has two 0.8mm holes.
Here are also some threads I found (in German though):
To test the influence of the hole area, I turned a small nozzle with four holes, each 0.8mm. This results in a total surface area of about 2mm². But four holes is too much for the Gaggia - even with a PID. The milk gets hot too fast and is not easy to control. For a larger pitcher this is OK, but as I use the 250ml most of the time, I decided to give three holes a try.
And what can I say, three holes seems to be very good!
Soon-ish I'll try to recreate the nozzle with only three holes but in proper stainless. Or buy the one from Tidaka, as it looks really good :D
All you Gaggia Classic owners know the trick: Buy the Rancillio Silvia steam wand and put it on your machine.
Unfortunately, the new system with the ball joint does not fit the Gaggia, therefore you need to use the old one. (As I heared lately, there are conversion kits, which require to replace the copper tubing with some PTFE tube.) There are two type of them. One uses an external thread on the pipe, the other uses an internal thread. Both have the same problem: The thread will not seal, therefore there is always water coming out of the thread instead of the nozzle.
And there is another problem: If you are not careful, you damage the pipe while fixating the nozzle! It happend to me on both types of the wand...
On the external thread pipe, the nozzle broke, on the internal thread pipe the pipe broke...
So, it was time to create a new, better system!
In my opinion, both systems have a huge disadvantage: They have too many corners which are not so easy to clean. Also they are quite short, therefore milk will always come into the gap between nozzle and pipe. And this is almost impossible to keep clean!
So, I thought about a better solution: The nozzle itself should be mostly round and much longer than the old one. Idealy, it should stick out of the milk, thus there is no gap where milk can get into.
A first sketch in FreeCAD was created:
Next, I bought some 8mm stainless steel rod (1.4301) and created the nozzle out of it. Then I cut the pipe and added a new thread on it. The thread is a metric fine, M6x0.75, as the wall thickness of the pipe is just 1mm. I used the same thread as it was on the pipe before.
Of course there are some things you need to take care of. I noticed that the nozzle would start to corrode after a few usages on the inside. Someone told me, that you should not mix tools for mild steel with the ones for your stainless, as particles will migrate into the material and corrode there. Therefore I ground the inside of the nozzle as good as I could.
The outside was ground using 2000 grit sanding paper, which leaves a nice mirror finish!
Here is the finished result:
The thread is sealed using teflon tape, and you maybe have noticed that I did not put flats on the nozzle. It turned out that you can securely mount the nozzle even if you apply the torque just with your hands! Therefore I decided not to create the flats, which would result in extra edges that are harder to clean.