Thomas, any updates? I'm enjoying this project and need another fix!

Ha! Yes indeed, a fair amount of work has happened over the past few months, but much of it isn't much to look at, as it were. Mostly, I've been finding suppliers and waiting for parts to come in. Metric copper tubing, once lost, now is found. Similarly, crush washers, thermocouples, metric pressure gauges, a giant G-1" tap, steam wands, hot water and steam taps and a whole host of other sundries. I've also been chipping away at the sheet metal design and waiting for a friend to sneak some brass samples into a gas-spectrometer at his work.

I'll post some pics in the next little while.

Happy to hear that progress is being made
Looking forward to more updates.

As promised, a couple of photos of the work done over the last little while.

First up, a tiny bit of plumbing, which is pretty much where I stopped on the build itself for want of a bunch of parts and time to work with them.





This was essentially a trial run to figure out the best way to bend the tubing and where to put the pressure gauge. I used North American 1/4" tube which is really close to the 6mm it is supposed to be but waaaaaaaaaaay cheaper because of the absence of the novelty factor. I welded a socket head cap screw onto the frame to act as a stud and then machined some a spacer to get the pressure gauge set back at the correct distance from the plane of the back splash. This is just a temporary measure until I sort out exactly which adapters and gauge will be used - then I'll design a bracket with the appropriate forward/aft offset and up/down & port/starboard tolerances.

I sourced a couple of tools for bending the copper tubing but in the end because some of the radii are super tight, I built a some custom tools that can be dropped into the bench vise.







I was pretty sure these tools would work really well for small diameter tube, but I wanted to try to make the main HX tube the same way to avoid having to hard braze the connections (silver solder ain't exactly cheap...).

Starting with some heavy-wall 3/4" copper tube. First we heat it up to cherry red to anneal the copper.



You can't see it in this picture, but once it cools, it's the color of eggplant, I swear.



Fill up the the pipe with sand to stop the walls from collapsing during the bend.



Install the big bender in the vise and tighten the vise.....





little...



by little....

Great pics! I love the custom tools.

The next step is to throw everything away and start over.

What I didn't notice while I was happily bending the tube is that the inside die, which is made of plywood, had split and allowed the tube to crumple. The outside of the bend looks great, but the inside was a mess. Likely, the tubing is work-hardening as it bends and needs to be re-annealed a couple more times. Also, the setup would be much stiffer if it were in a proper arbor press with metal dies. Given that the flow rate through this part is tiny, it wouldn't have made a difference but as this proved not to be a viable method for making a bunch of these, I went back to the original plan of hard brazing parts together.

I've done some sheet metal in the past, but not a great deal. I decided that it would be a good idea to try out something small to see what can be done in house and what needs to be outsourced. Cutting is cheap, but bending still requires lots of manual setup and is consequently expensive for small runs.

I don't know about you, but I make a mess when I pull a shot. I've seen a bunch of solutions to the problem (including a miniature vacuum cleaner!) but I thought I'd come up with one of my own.



I had access to a shop with a shear and box pan so I tried out a couple of tests in aluminum to work out the bending order and to verify the proportions. I glued on the tab to hang the brush as cutting it is out is pretty much impossible with hand tools.





Real parts in 20g stainless ready for polishing and bending:



This was a good exercise to test out the design tools and supply chain for the far more complex parts for the bodywork; almost all of which will have to be fabricated with grown-up tools that I don't have.

Have you done much trials on the performance of the horse shoe style HX compared to the straight tube HX?
I know more recent Aurora like mine and machines like the brugnetti C-1 have all moved to the latter.

That is a very interesting question. From a fabrication stand point I like the trombone or horseshoe as the parts are replaceable. I have one of each versions but I haven't done any quantitative measurement to compare them. If I had to choose on the basis of the quality of the shot I think the straight through might win - but only just barely. And this may well have to do with other factors - different boiler temp, grinder, line pressure etc.

Moving to a straight through design could be a cost cutting measure as there are fewer parts.

At some point, I will have to get some proper measuring equipment and do some testing.