|Drawing B1 - Formers, Materials
||1. Barrel and Ring
||The barrel has been machined to length by holding in
the bore and supporting the other end in a steady. My steady wasn't large
enough to use the rollers so I set some PTFE pads on the outboard ends of
the arms and then reversed them. With a drop of lubricating oil, they worked
fine. This isn't locked down yet but it shows the pad in place Although
it had been sawn reasonably square and didn't really need to be cleaned
up, I faced about 20 thou off the first end. However, for some unknown reason,
I ordered an overlong piece and decided to part the surplus off. The ring
will come in handy one day. I cheated, though, I only parted about three-quarters
of the way through then hacksawed the last bit before finishing the face
with the parting tool.
|| The barrel ring was made using the lump of bronze that
I had originally trepanned from the Britannia front ring. Once again, I
started by trepanning out the middle, going half-way through then reversing
the billet. Rather than just turning the outside into swarf, I cut a thin
ring from the outside as well. I don't have a use for it yet but oneday...
These are the three billets that were produced, the middle ring the one
that is needed. I hate wasting material of this value.
|| The outside diameter and one face were machined square
to each other, then the billet was loaded to soft jaws and practically all
the machining done in a single operation; two bores, the front spigot and
the o/d with it's radius. The radius tool is just in the picture. The offcut
from the tube was used as a gauge. That left nearly 1/8" to come off the
back and the spigot for the smokebox backplate to be machined. A register
was turned on the outside of the soft jaws and the work held in the front
bore. Then it was faced to length and the spigot turned to finished size.
Most of the machining was done at about 350 rpm and using the feedbox whenever
I could. This is the barrel with the smokebox ring fitted to the end. A
few countersunk brass screws will be used to hold it all together and these
will be concealed beneath the cleading.
|| I've now made a start on the rest of the
items needed to construct the boiler and the first things I made were some
formers for flanging the various end plates. I have made these from 20mm
MDF as I have used this before and found the material works a treat. The
front and back firebox plates are the same size and have a large radius
at the top corners. I drilled a 5/16" diameter hole at the origins of the
two circles and used these as pivot points on the rotary table. I also machined
a small radius to the outer edges using a router cutter so that I dont end
up with a sharp corner inside the flanges. Two other formers were made at
this time, one for the front tube plate and one for the backhead but I will
make the one for the throatplate once I see get the outer wrapper shaped.
The second hole in each former gets used as a means of stopping the work
rotating about the pivot by clamping to a tee-slot.
|| I decided to make the front tubeplate first
using a piece of 3mm copper. I roughly cut out the shape, then placed it
between the former and a solid backing plate and held it in a bench vice.
Then it was a case of some firm tapping followed by annealing at red heat
and plunging into cold water. The plunge isn't strictly neccessary as the
copper goes soft anyway but it flakes off any scale and speeds the job up.
It took two annealings to get this far. I was cutting off surplus waste
with a hacksaw as I went but it was getting more difficult to keep the shape
the further round it went so I used the lathe to trim it down when I was
about ninety percent of the way there.
|| Once I had the copper firmly on the former
all the way round, I then skimmed the O/D and faced the back. The only way
I could find to hold the tubeplate was with my 4-jaw SC chuck because the
3-jaw wouldn't go down far enough. I turned it to about 10 thou oversize,
then trimmed it to length using a left-hand tool. The barrel was then returned
to the lathe and mounted in the fixed steady so that I could bore it to
fit the tubeplate. It needed to be 1.1/2" deep to allow the plate to sit
at the correct depth. I only use those super-sharp polished carbide tips
for turning copper because ordinary tips tend to be useless with soft materials.
|| By having a small shoulder, it also means
I dont have to use any fixings to hold the tubeplate in place at soldering
time, gravity does the job for me. At the moment, it's a nice sliding fit
but it will probably become distorted during the various operations between
now and then so will needs tweaking at the time. Then it was time to put
the holes in and this was done on the mill using the DRO to locate them
all. I used an 8mm drill to start with, then followed with a series of slot
drills to get the holes to size. The 10mm tube holes needed the reamer run
through and the superheater tube holes were bored but the three remaining
holes were just left at whatever as the bushes will be turned to fit. Offcuts
of tube were used as gauges.
||More of the boiler parts have now been made including
the firebox endplates and the backhead. These have all been melded around
their respective formers and the workshop became quite hot with all the
annealing that was needed. In case anyone has never annealed a piece of
copper and was wondering how hot to get it, it's this hot! Because the formers
won't be needed again, they were used to support the work while the edges
of the flanges were machined to size. The copper is still very soft at this
time and will bend away from the cutter quite easily. I used a 1/4" diameter
end mill to trim the edges, going round in a clockwise direction (climb-milling)
to give the material maximum support.
||The former was also used as support when I milled the
endplates to length. The firebox tubeplate was drilled in similar fashion
to the front tube plate, the rear tubeplate has had the firehole bored to
size and the backhead has been fashiond around another MDF former. The tubes
were expanded at the back end by about ten thou, then skimmed back to just
under 10mm so that there is a tiny shoulder for the tubes to rest on when
silver-soldering. Nothing is needed at the front because the front tubeplate
will rest on the lip in the barrel.
|| Some 6BA bronze screws were made and these have been
used to fix the wrapper to the end plates. I don't like rivets for this
because they don't holed the work firmly enough. Also completed was the
holes in the barrel for the forward clacks and the large steam-dome hole.
The front tubeplate was used against the chuck jaws as a depth-stop and
an MDF former bolted to a faceplate acted as the support for the other end.
After drilling and reaming the two clack holes at plus and minus 90 degrees,
the rotary table was set to zero and the big hole roughed out with a hole-saw
before boring to size. Once this was complete, with the rotary table still
set at zero degrees, a scriber was mounted in a drill chuck and dragged
along the full length of the barrel. I didn't do this on the Britannia boiler
and had alignment issues because of it.
||The outer wrapper had a centreline scribed
at the half-way point and was simply folded around the barrel, followed
by bending back to form the waist and creating a nice fit around the backhead.
Then it was on to the throatplate. This was the most difficult part to make
because of the reversed double flanges and I cut the raw material a good
one inch bigger all round than the suggested starting size. I also cut a
packing piece for the front of the wrapper, clamped the backhead to the
bench and temporarily assembled things to get a feel for the finished shape
and size. The offcut of tube was used to mark where the barrel reaches to.
||Learning from my experience with the Britannia boiler,
I decided to get the side flanges fully-formed first and a piece of MDF
was made into a former. I could have cut down the backhead former and used
that but it was just as easy to make a new one. No pictures here, it was
just simple folded-over sides. The former for the barrel flange was a little
more complicated and a piece of oak kitchen worktop was used to make this,
squared-up all round and milling out the middle to support the side flanges.
The top was shaped using a 110mm hole saw. The first former was cut down
to act as an internal support but allow the flange to be formed and the
throatplate was placed in the former and the flaring at the top beaten into
place. Some of the waste area was marked for removal and was cut out with
the Abrafile before I started to form the barrel flange.
||I found early on that the sides of the former would need
support and a large clamp was used with the rest just held in a bench vice.
I don't have any special hammers for copper-forming and a one-foot length
of 1.1/2" diameter stainless steel was used instead because of the concave
form. Between the many annealings, I kept returning to the mill to remove
excess material because the further I went, the harder it got to keep the
shape. This is the point that I decided to call a halt to the bashing and
bring all the flange widths to size although the picture was taken after
thinning the top wings.
||So this is a trial assembly to see how well things fit
and it's not too bad. The circular shape wasn't perfect, however so I decided
to skim a little off the inside using a flycutter. I don't have any left-hand
tools for the boring head so set up a right-hand one and ran the mill in
reverse. This promply unscrewed the head from the mandrel so I had drill
and tap a hole in the side to accomodate a locking grub screw. After that,
I milled the diameter to a near-perfect fit. Once again, the former acted
as a support for the soft copper and the opportunity was taken to scribe
a centre-line through the workpiece.
||A pair of fixing holes were drilled in the barrel flange
and this was then rested on the barrel using a large vee-block to get everything
in line and upright. The holes were transferred through to the barrel and
a pair of 6BA holes tapped to take some bronze screws at soldering time.
Another centreline was scribed on the underside of the barrel, diametrically
opposite the top one. This enabled accurate alignment of the throatplate.
Another fixing was made to hold the wrapper to the barrel and the assembly
held together with clamps. I can now mark out a few more fixings knowing
everything is square and correctly aligned. I won't make any fixings for
the backhead yet, though, because things like the firehole ring and the
foundation ring will determine the final position of that.
||5. Outer Wrapper
||Before going any further, I wanted to make sure that the
firebox fitted as it should in the outer wrapper. With it resting on a piece
of 1/4" square material, it seemed to fit as it should. The backhead was
held loosely by the spring of the wrapper. Satisfied with that, I then set
about cutting the wrapper and backhead to length. The throatplate is already
to the size on the drawing and is square to the barrel so this was used
to mark across to the other components. The wrapper was given a good, long
soak in the pickle to clean it up for soldering and the three top bushes
||With the wraper now to length, I was able to mark out
and fit the two blowdown bushes each side at the bottom as well as the safety
valve and manifold bushes on top. The top faces and the thread were painted
with correction fluid , the outsides coated with flux and the holes in the
wrapper fluxed as well. This last may seem unneccessary but I have had failures
in the past for ommiting this step. I think it's about wetting the surface
to break surface-tension. On the underside, the bushes protruded about 1/16"
and solder rings were placed over these. I'm using 40% silver solder for
all my bushes, which will all be fitted first, and 55% silver solder for
everything else. More flux was added on top of the solder rings. A hearth
was build from Celcon/Thermalite-style building blocks and the wrapper placed
as shown. The bushes are kept in place by resting on the thin piece of block
and the side blocks keep the wrapper upright but also enclosed to preserve
heat. If the workpiece was out in the openm it would spend much of the time
radiating the heat away again, wasting it. Lifting the wrapper in this manner
allows me to apply heat from below to draw the solder through.
||After a single heat-up, followed by gentle cooling and
a spell in the pickle, I have a perfect set of joints with nice fillets
on both sides. They may not be the prettiest and I've used more solder than
needed on the manifold bush, a full ring of 1.0mm solder rather than a partial
ring that I used on the other two. This shows the importance of good preparation,
it's too easy to get complacent and then have to remake one or more joints.
The two blowdown bushes were done one at a time and this is how it all looks
with the backhead clamped in it's approximate position. .
||6. Dome Ring
||Looking for a piece of suitable material, a friend produced
this nice lump of cored bronze that's just right for the job. I decided
to turn the outside form first and also make the dome ring from the same
material. The o/d is finished at 2.1/2" dia and the spigot at 2.1/4" to
fit the bored hole in the barrel. Parting off was a little interesting,
using a 1/16" parting blade sticking a loooong way out of the holder. Sawing
off would have wasted too much material and this stuff ain't cheap! The
dome bush was reversed in the chuck, given a light skim across the face
and then bored out to 2" diameter, leaving a 1/8" thick ring at the bottom
with a 1.1/4" diameter hole through it.
||Moving to the mill, I cleared away some of the base to
leave a pair of mounting lugs for the regulator mechanism. I also drilled
and tapped a dozen 4BA holes holes in the bush and a matching set of clearance
holes in the ring. I need a short length of 2" dia copper tube to silver-solder
into the ring to form the inner steam dome. A pair of 4BA clearance holes
were also drilled in the lugs. Don Young doesn't give any details about
the regulator - use standard LBSC fittings, whatever they may be - so I'm
going to use a "regulator in a tube" method. Although the assembly should
be completely below the dome bush, I have relieved the front and back sections.
The two lugs will provide a fixing point for some sort of cradle.
||It's impossible to make the gauge glass arrangement look
anything like the prototype and still function properly and the backhead
of the model only bears a passing resemblance to the full-sized "Calbourne",
anyway. The upper bush is the one that causes the problems and DY drew up
a flimsy bracket with a couple of bits of tube soldered together that looks
awful. My effort doesn't look any better but is a fair bit stronger. To
allow for replacement of the complete gauge glass assembly I made a bush
from hexagon bronze, drilled and tapped 1/4" x 40 tpi the same as the fixed
lower bush, and soldered a short length of 1/4" diameter thick-walled copper
tube to it with 40% (high temp) silver solder. The backhead was clamped
to an angle plate and a matching hole made with a 3/16" diameter slot drill.
Then the upper bush assembly was set in the hole using a spacing gauge to
set both height and orientation.
||I've chosen hexagon material because I will be able to
support the bush with a spanner when I tighten up the top fitting. The lower
bush has also been soldered in with 40% solder, as will be the fitting-to-backhead
joint. That way, I should have no problems when it comes to closing the
boiler. Although it looks a bit silly at the moment, once the cab front
is in place, it will blend into the background. The drawing shows the position
of the upper bush suspended in mid-air.
||This is the completed assembly set into the boiler. A
small notch has been cut to allow the backhead to sit in the correct position
but there is still plenty of flange available for soldering at final assembly.
Following advice, I've also cut the inside part back flush with the inside
of the backhead.
||8. Steam Dome
||I've redesigned the dome to suit my particular regulator
arrangement. My steam collector tube will be a bit shorter and I won't need
a gasket. A coverplate was made from a piece of the bronze and a piece of
brass tube was parted off for the upper section. The first job was to turn
the O/D to 2.500" diameter and machine a shallow spigot to locate the brass
tube for soldering. The rest of the turning was done in soft jaws, much
easier to hold the workpiece with these. First, they were machined to grip
on the O/D with clearance for the spigot. For anyone unfamiliar with soft
jaws, here they are being machined. One of the chuck key holes is identified
with a mark and I only ever use that particular one when machining the jaws
or loading the work. It compensates for any looseness in the scroll.
||I didn't fancy trepanning out the whole billet on the
first op but it was worth saving the ring on this next one. These toolposts
are pretty flimsy affairs at this size so the G-clamp protects it against
a dig-in which might break the tool holder lock. That came away fairly easily
and I expect there will be a use for the ring somewhen in the future.
||The front was turned to a bare 2" diameter to fit the
dome bush, then a 3.5mm wide undercut was formed to take an "O" ring. If
it snags, the centre will stop the work climbing out of the chuck and breaking
the tool. After the picture was taken, the centre section was cored out
to leave the coverplate 1/4" thick for the filler plug. This gives a little
extra height for the steam collector tube. The holes for the mounting screws
were drilled on the mill, as was the M14 x 1mm tapped hole. I have offset
this to the front so that water doesn't pour down the steam collector which
sits at the back. This is the plate resting on the dome bush.
||The filler plug was made from 5/8" diameter phosphor bronze
using a button die for the thread. The flats were milled by holding the
workpiece in a hexagon collet block and rotating round in the milling vice,
finishing at 12mm AF. The "O" ring collar was made from a piece of 1" dia
brass, bored to fit the 5/8" dia PB and further bored to 3/4" diameter by
80 thou deep. The setup shows the clamp doing two jobs, holding the thread
and acting as a depth-stop for the collar. Before silver-soldering the parts
together, the thread of the plug and the reccess in the collar were both
covered in correction fluid because it would be extremely difficult to clean
up if the solder should run away. After that, the brass tube was soft-soldered
to the top of the coverplate to act as the filler reservoir. These are the
parts cleaned up and fitted with "O" rings, ready to assemble.
||One of the guidance principles of the HSE is about restricting
access by untrained personnel and many things require the use of a tool
to access, adjust or remove, the thinking being that if you are able to
use the tool, you probably know what you're doing. This bung requires the
use of a tool to remove it, satisfying that requirement. It shouldn't be
difficult to find a tool at the club. Here it is, mounted on the dome ring
and looking very similar to the earlier version. The larger reservoir should
make filling the boiler even easier. The thinner mounting ring is also better,
allowing the screws to go in an extra thread or two.
||9. Next Item...