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 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.
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.
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....
Next 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...).
The boiler plate had to be redesigned because I couldn't find a heating element similar to the original design. The element I chose has a male 1" G-thread, which requires a matching female thread to be cut into the boiler plate. I didn't really want to attempt this in the stainless part I had cut so I bought a 316 stainless bushing adapter and cut it down to fit the hole in the plate. The adapter was brazed into place (rather than welded) to keep the distortion of the plate down.
The inside...
and the out.
A month has flown by but there has been some progress on a number of fronts.
First up, the frame. This $150 (Canadian!) bender from Princess Auto (Harbor Freight's distant cousin) is actually capable of working to a surprisingly high tolerance. It is one of those this-looks-simple-so-why-can't-I-figure-it-out tools. After reading, re-reading, re-re-reading and then finally throwing away the manual I looked on YouTube to find similarly baffled owners. Once you do figure it out though, it will produce parts with two bends in this 1/8th cold-rolled stock to within 1/16th of the desired dimensions.
Vertical posts tack-welded and clamped to the two parts of the base of the frame.
Setting the cross bars that carry the boiler in place and the corner braces to which the feet will also be attached.
Test fit of the boiler (which still has its square pressure-test plate on until I finish the actual boiler plate).
Concluding the day's posts: I needed to make a couple of 1" BSPP (G-thread) x 3/4" copper sweat adaptors that will form the ends of the heat exchanger tube and make the seal with the boiler plate. These are necessarily custom parts as this they adapt from European to North American standards. However, I think that is it reasonable to consider the HX tube as a non-serviceable i.e. a custom part.
Lead-free hex stock after threading, chamfering and cut-off operations.
View from the other side showing the 90 degree included-angle internal chamfer that will seat and seal with the hemispherical "bi-cone" fitting.
The part is flipped and bored to receive the 3/4 copper pipe.
Test fit of the pipe.
