Boiler part 3 - brew reservoir weldup

Everything seems slower in August. The weather is good, the city has a relaxed atmosphere and somehow, sitting indoors in front of the computer is less attractive than it is in February. I do have some progress to report however. First, the brew reservoir is pretty close to completion. I tack welded on a couple of pretty hefty lugs that will carry the whole load of the boiler when it is attached to the frame. Then I brazed the G1/4" fitting in place. The fitting, by the way, was cut and tapped on the lathe from lead-free Ecobrass hex stock - which, though a little more difficult to machine than leaded brass, turns out to be pretty good. I have done quite a bit of soldering in the past but never any silver brazing - so I was exited to see how this would work. The white gunk in the before shot is flux which prevents atmospheric oxygen reaching the metals in the joint and oxidizing them as they are heated. Using an oxy-acetylene torch, the base part is heated evenly until the assembly reaches the melting point of the brazing metal (~1145 to 1650°F (618 to 899°C) depending on the brazing alloy). Just like with soldering, once the right temperature is reached, the liquified braze is drawn into the joint by capillary action. The hard part is actually to not overheat the joint - the oxy torch is a powerful beast - that and the cleanup afterwards which is a royal pita. This part just needs the final structural welds on the lugs and then it can be welded to the boiler tube.

Boiler part 2 - boiler tube

So, on to the boiler tube!

This is a piece of 6" schedule 40 316 stainless pipe. It looks quite innocent and happy on the lathe in the picture. Cutting it, however, was not so easy! It is held at one end nicely by the six-jaw chuck from the inside. The other end, however, is completely unsupported. As it isn't even sort of round, it can't be clamped externally, so the only way to hold it is with an elaborate internal expanding plug - which would take a day or so to make. As this is a part which will likely be laser cut when I need more of them, I didn't want to go there. So, with the lathe on dead-slow and taking extremely light cuts (0.001" per revolution) with a carbide parting tool I cut it unsupported. As the setup is not even sort of rigid, the tool tends to chatter a bit, which has the effect of resonating and ringing the tube like a bell. REALLY LOUD! Even with heavy ear protection, I could feel my back teeth buzzing. Still, it did a good job and the end result is a very clean edge about as perpendicular to the walls as you can get.