2008 - 2009.

John R. Bentley 2009.

Model Watertube Boiler

-  A miniature industrial D-type boiler  -

Starting the silver brazing on the boiler:
In North America, when conducted above 1100 F°, hard silver soldering is called silver brazing.  The old loose term, "brazing" is now called braze welding.  Meanwhile welding refers to melting the parent metal and using a nearly identical filler without the use of capillarity.  According to their website, this is the word of the American Welding Society - and apparently has been for years.
Up to Feb 22, 2009:
I picked up an extra roll of copper tube for the job
 (that brings my supply for the job to 50 feet - about 16 metres)
I have been slowly reaming all the boiler tube holes in the drums for the required entry angles.  It is a lot of work, making tubes, then mocking-up portions of the boiler against a drawing - just to determine these angles.  The incessant hand reaming doesn't do much for my shoulder and back muscles either.
Holding and turning the chuck by hand to get precisely the effect I need

Final reaming to size:
holes for the two safety valve bushes ( not bushings! )
(that reaming is being conducted in my new drill press)
OK - here it starts:  Tubing the Boiler
Three lengths of tubes
(there are still 28 boiler tubes yet missing from this picture)
Here is my latest (and first) bending tool
Split grooves surround the tube
Test-fitting four tubes in the boiler's convection bank
Red marks are from a grease pencil - not blood
The three empty rows plus back side of existing row make up the convection bank
(the D-shaped water-walled furnace will be constructed beyond the existing row)
Another view
The dots on the tube spell:  (MADE) "IN CHINA"
Just a B&W photo to show the eventual layout
Here's the cover (roof/walls) unit - standing on end
The D-shaped furnace area is visible here.  Insulation will eventually surround the entire inner unit.
Of course up until this point the tubes had only been tried in position.
I started brazing yesterday afternoon.  It was a bit of a comedy after the first row tubes was brazed-in to one of the drums. Apparently I had made some sort of miscalculation on the diagram and they were too short to span between the drums while allowing the overall size of the assembly to be correct.   hmmm.....this could be old age.  Anyhow, I re-melted the brazing alloy and pulled out all the tubes.  I pickled, cleaned, re-reamed the holes and installed newly-made tubes.  Fortunately it was only one bank of eight tubes - it could have been a whole lot worse!
Still hot - and blackened!
This was the second set of tubes brazed into these very same holes yesterday...
In future I vow never to draw a diagram again on critical jobs
(I will measure everything - in position - instead)
After the pickle
those joints turned out well
The silver brazing alloy has penetrated the joints well
We'll just see how all this turns out after all the brazing is finished!
I have to place a large baffle behind this row.  Due to that same defective diagram, I also must further ream two rows of holes in the lower drum again to suit the newly-increased angle created between drums by the slight change in length of the curved-end tubes.   But I'm having fun :-)
Dirtywork to come -

NEXT: Part 4  
the Great Tube-Brazing Episode.