So this is the tool that's used to make the steam tips. For those who are unfamiliar the brass is mounted in the chuck on the left. It's then spun at high speeds and metal tools are used to cut it.
A steam tip is a small socket with a hole in the end. The size of the hole dictates how much steam will come out. A big hole means a lot of steam can come out, but this can be bad. If you're planning to steam a small amount of a milk a large hole will heat the milk up too fast. This hole is for a small amount of milk and is 2.5mm in diameter
First the part is faced and cut down to a 12mm diameter
A 45 degree cut is made in the tip to add a chamfer to the part.
A small hole is made so the tip can be hollowed out.
An 8.5mm Dia hole is drilled into the part at slowish speed
The depth of cut needs to be right up until the point where there's a chamfer.
The steam hole is slowly drilled through the part
The tip is then tapped in the lathe. I use a hand tap and just rotate the lathe by hand. Different machines will need different threads. The Wega commerical machine I did needed a M10x1.25 thread, whereas the Rancilio Silvia needs a M10x1.0 thread
I added a knurl so the part can be taken off easily. Brass will change size as it heats and cools. This can make it tricky to unscrew if it's hot, so a knurl helps here.
The part is then parted off from the tail stock
The surface is very rough at first so the part is turn around and finished with a facing cut
The original steam tip was flat on the end but I added a counter sink so the steam has some space to expand when hitting the milk. I find this allows for finer control for the barista.
So there's a slight difference between these two tips in the length of the chamfer, all things considered though it came out okay.
This tip is installed on the machine and the Royal Yacht Club of Victoria. It allows a barista much finer control over steaming milk. A set can be made so different sizes can be trialed at will.