2008 - 2009.

John R. Bentley 2009.

Forced Air Burner Assembly

-  For the Model Watertube Boiler  -

The burner and boiler face with piping and accessories yet to be added

To recap, the bare boiler pressure vessel, casing and stack were completed before the beginning of Summer.  This Autumn I started on the burner and windbox assembly.  A Cleaver Brooks BR burner type from the late 1970's is being used as a rough guide, but it will not be an exact scale replica of any particular one of their three BR versions.
Don't expect anything too clean and neat to be shown in these pics - raw fabricating is still the rough work:-)
The BR was one of three types that were available in the period I have chosen for my model.  I have the company's simplified drawings with dimensions.  I plan to follow these as to proportions, but I'll reserve the privilege to only use them as an approximate guide, since my fuel is different and some excessively small details are not appropriate to a boiler that is to be used as a shop test unit.

Here is a view of a Cleaver Brooks packaged boiler burner from a 43-year-old brochure

I will make this burner in two parts that will push together - the top fan unit and the lower burner/plenum/control box assembly.  Not shown in this picture is a fold-down operator's platform at the level of the bottom of the legs in front of the fuel train.

- note:  the above image was taken from old Cleaver Brooks brochure and is included here under a fair use policy only to demonstrate the direction I am following in this hobby project. I will not do battle with anyone representing the company on this matter and will willingly give further credit or remove the image upon their request.

Paper cutouts were my starting point

The very first brazed joint of the building season!
It's the bottom corner of the air plenum (just above the left leg)
It is being brazed over the edge of the anvil on my vise
Air plenum
with backplate installed
Ready for brazing in the frontplate (left)
Note the backplate is two overlapping pieces.  This is to help reduce air leaks since the bottom half will slide out for lighting and servicing.
Marking out the fan housing on steel plate
Bending the edge
This is stiff steel - needless to say I didn't bend it around that plate, but used a heavy piece of pipe.
The windbox in waiting:
Some basic pieces for the blower and air plenum
The unbrazed mockup
Silver brazed fan guard
(back view)
Front view
Backplate brazed-in and chain-drilled for removal of the fan opening
Back view of the front plate and spacer
Cracks left for brazing
Rough brazed - nearly finished
- except for large rectangular flange around the bottom
(The color you are starting to see is copper plating from the brazing pickle)
Making the flange
Cutting out on the bandsaw
Chain drilling fan housing frontplate
(note the flange is installed)
 About to start making the four large openings in the windbox assembly
                                                                                  I love old black and whites
This will be the front hole of the burner, visible on the completed boiler
(it will be covered by a flat circular plate with a small fuel tube entering the centre)
More chain-drilling
Hacking out the hole for the blower
(a larger flat plate will cover it with the motor protruding from the centre)
Using a Sherline boring head in the Taig mill to smooth out that mess
Boring completed
(some copper plating from the pickle is still remaining)
The prototype burner has three electrical control boxes mounted on the front
I am including them just in case I need space for any hidden connections
The frame is tacked with silver solder
I haven't progressed with these electrical cabinets too far to date -
the front doors are cut but not yet mounted
The three main fabricated components for the BR Burner
(there is a two-legged assembly yet to be attached to the bottom
and possibly as well - a folding front platform, a signature Cleaver Brooks option)
The burner tube under construction
I turned it from solid 12L14 steel

(it is stepped to match various layers on the windbox)

This will be the connecting tube between the burner assembly
and the firehole in the front of the boiler casing.  It will carry gaseous fuel and air through the addition of venturis and mixing tubes.
Boring the passage
Back view of the burner tube
(the super thin part at top enters the boiler's firehole)
(that pic is a bit fuzzy - I took it while having lunch in a restaurant and the light was limited)
Here's the tube screwed to the back of the lower portion of the windbox
(note that the burner's bottom leg assembly is seen here on the right side)
Drilling the blower front cover plate
(in the Taig mill)
Completed blower front plate with motor attached
(the brass pinion will be removed and the wires re-routed outside)
Trial of unfinished blower motor on the upper portion of the windbox
Size reference: comparing to a loupe
(the motor housing is still not yet completed in this shot)
Adding detail to motor end cover
North American electric motors with front flange (C-face) mounting often include the bottom mount as well.  The horizontal mount is a great convenience when placing a large and heavy motor on a bench for servicing. The thought of a 200 lb motor rolling onto a concrete floor is not pleasant :-)
Starting to make the motor's bottom cradle and mounting foot
Bored to fit around the motor housing
Milling the bottom flat
Test fit on the shell
Bottom plate - to later become the mounting feet 
(high-temperature silver brazed to avoid coming apart during subsequent brazing)
Motor housing slowly coming together!
A mock-up of how it will look
Starting to make the motor electrical connection box
(off-centre turning by using square stock in a 3-jaw chuck - I use this trick often)
A rectangular loop of soft iron wire has been formed and mounted diagonally
Fluxed and ready for brazing
Setting up for silver brazing the box on the right to the motor
Whacking in pins to suggest motor bolt hole locations
(I really don't know the word for those things... lugs? bosses? ...)
On many motors with there is a strengthening rib cast-in
across the diameter of the rear end bell
(I have banged in two plates which will be subsequently milled down)
(a lot to finish yet)
A quarter-inch endmill does the trick
Trying the wiring through the electrical box on the side
(the motor is a very common 4-6v Mabuchi model used in optical disk drive drawer mechanisms (DVDs) and they are widely available.  I have three new units)
A quick coat of high-temperature paint to check out the appearance
In the scheme of things, visually this is a small and insignificant part of the boiler
(I didn't take the detail beyond more than an approximation of a typical 1970's motor)
The front face threaded mounting holes are visible here
In position on the blower
A rough mock-up of the entire burner lying flat
If the operator's standing platform is added to this model, it will extend out from below the bottom of the "legs" which are well above the floor.  A piece of armoured cable will extend from the bottom of the electrical box on the motor's right side, straight down to the U-shaped control boxes below.  Of course there will be considerable fuel piping in the lower area for the vaporizer and burner as well as the return connection to the tank.  There might be piezoelectric ignition or I may just use a match.
Here is the view a person would see if approaching a full size version of the boiler
This is to be a working unit and not really a model, so heavy steel materials were used to fabricate a durable unit at the expense of anything like perfect scale or detail.  I simply wanted something that looks like a boiler plant for testing or demonstrating runs of my smaller engines.  I can't fix a proper time frame, since my range of models spans different eras, so I felt an old-fashioned-looking, modern boiler might be preferred to a modern-looking, old-fashioned boiler.  If I want it to look modern I will paint it Cleaver Brooks' light metallic blue and if I want it old, I can paint it flat black and leave some shiny brass fittings. 
Testing out methods of making armoured cable
Earlier that day this was an aluminum knitting needle...
Drilling it out for the wire to pass through
This is only a trial piece - I'll make a better one :-)
Here is the approximate position it will take
A junction box at the loose end will hold it secure.  Then a moving contact on the lower removable part of the burner assembly will make the connection when the burner is pushed into position.
I felt it was time to start making moving parts for the blower - a change is as good as a rest they say....     I am including a few more pictures:
I knew that someday my boiler burner blower would need one, so I made a start a couple of days ago:
Lopping off a block of 6061 Aluminum
Turning a chucking piece on the end
Starting to form the impeller eye
1/4" ball endmill
The beginning cuts for the first blade
Three blade segments roughed out
The initial cuts complete
Round Two
(these short cuts are parallel to the other sides of the blades)
Nearly complete - yet to be accurately sized
Propping up the Dollar !
A sense of the scale
It fits in the opening but it is still somewhat too deep
The blades have an angle to the radii to "cut" the air as it enters the eye
(note how they don't point directly toward the shaft stem)
Rotation: clockwise
At this point I began trimming the impeller to size
Then an oversight led to a horrible event -
You will notice that I forgot to engage the tailstock centre into the shaft hole on the impeller!  Part way along, the tool dug in, swivelled the toolpost into the job and that little fan went into orbit, rocketing over my right shoulder at the square of the speed of light.
I wasn't wearing my face mask, I was alone in the house - but I was very fortunate.  However a day-and-a-half's work on the wheel was put into jeopardy.   I should have used the Taig lathe for this job, but it was clean at the time and I didn't want to get it dirty.
Of course that old fan never quite looked the same again!
(Repeating for emphasis)
A monument to my sloppiness
I had a long think and decided to try to repair the device before throwing in the towel and starting from scratch.  (I am trying to save the rest of that 6061 Aluminum bar for some future IC engine)  So back it went, into the lathe to be turned down to size, after straightening the blades with a screwdriver.
This time I used the centre!
The outcome is a usable impeller
It still seems to spin well on its shaft, so I think the initial balance is OK
Next thing is the intake housing and a start on the steam turbine housing, which will drive this impeller.
The egg-shaped intake housing plate
(the back side)
The impeller blades fit between the two raised rings
Impeller sitting in position on the inner side of the intake plate
It will look like this, but an air scoop will cover the eye
Air scoop roughed out
Air scoop brazed in position on the intake plate
(a plate and the turbine casing will cover the "U" except for a rectangular air intake at the top)
Overall shot of the back of the burner
Starting the steam turbine housing from stainless steel
I think high polish will be beneficial - considering the speed of the turbine
The lathe's rotating centre is useful for parting off stainless steel
A parting shot
(we've all used that line before)
The upper portion will look essentially like this
 (when the round turbine housing is brazed to the air scoop)
Probably I will silver braze three or more lugs to the outside of the turbine housing
(to allow screwing on a back cover plate)

This view from above shows the rectangular air inlet

The back of the turbine housing is still not yet completed. A debris screen will cover the inlet opening, keeping flies etc. from entering the duct and clogging the burner. 

At this point in construction I really needed a change, so in the beginning of 2010 I started machining the castings for a Stuart Compound Launch engine which is covered elsewhere on this site. That job used most of a year and with other things happening work on this boiler didn't resume until the construction of the stainless steel fuel tank in late 2013.