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This page: Explanation of flanging boiler plates

  Part 1     Part 2     Part 3     Part 4   Extra part 4a

Step one
The former plate

What you need is a normal former to make the throat plate (i.e. made of 10
mm steel plate) in the shape of the throat plate. The same plate can also be used for
forming the back head, if your belpaire firebox is parallel, but it is smaller in size as the final throat plate .
How much smaller in size?
I usually reduce the size of the former plate, by reducing the size of the
final throat plate (as on the drawing) by twice the thickness of the
material used for the throat plate (in my case that was 3 mm copper plate,
so the width was reduced by 6 mm, the height by 3) The material that is only
folded over a straight line will stay 3 mm in thickness (minus a very small
reduction if you hammer to hard with a steel hammer, but without reduction
of thickness if you hammer with a Nylon hammer) The material in the rounded
corners will gain in thickness by hammering (by clenching the material), but
this extra thickness (only a few tenth of a millimetre) is afterwards
easily removed by the aid of a file (which also smoothen up the surface,
which makes a nice joint for silver soldering).

Step two
The copper material for making the throat plate

Start with the round flange that will take up the boiler. There fore I used
a copper plate that is big enough to cover up your former + the extra for
the flanges themselves (don't forget that, and take enough for that..... in
my case (10mm thick former plate) I used almost 20 mm extra material at both
sides of the former (this gives you more 'play' afterwards). Indicate on
this plate where the centre of the hole will be (the hole that will flanged
to take up the boiler barrel)

Step three
The extra parts of the former

Now you need two extra parts, that are quite easy to make and use, if you
can get hold of the material. First you need to fabricate (a job for the
lathe) a steel ring. Height of the ring only has to be 15 to 20 mm. Wall
thickness of the ring has to something about 8 to 12 mm or larger. (so it
will not deform during the process. I used a piece of thick walled steel
tube that I had in the scrap box)
This ring will have a inside diameter that is the sum of : the outside
diameter of you boiler barrel + twice the thickness of you plate material
used to make the throat plate of (i.e. 3mm). But because the material will
be stretched you'll have a reduction in material thickness...........so 3 mm
will not stay 3 mm but can become something like 2.8 or even 2.6 mm
(depending on how high (deep?) the flange must be.....I use a flange height
of 10mm which gave me a final thickness of 2.7 mm) But you can work very
accurate here, by making the inside diameter of the ring firstly the sum of
the outside diameter boiler barrel + two times 2.5 mm (if you use 3 mm thick
plate). I'll explain how to use the ring in a moment, but let me tell you
now, that later on you can exactly measure the material reduction, and if
not ok. (probably to small when 2.5 mm used as calculation figure) you later
on chuck the ring once more in your lathe and now enlarge the inside
diameter of the ring to the correct value found by measuring on the job.

A second part you need is a disk (steel, hardwood or any other reasonable
strong material....I had a piece of Tufnol) that is about 15 to 20 mm thick
and has an outside diameter that is the same (or a few millimetres bigger)
than your boiler barrel. To the correct dimension I come in a moment.

Step four
More tools
As an extra it would be handy if you had a steel disk that is about 2/3 of
the diameter of the boiler barrel and about 40 to 60 mm in height and a flat
strong surface (preferable a steel/hardwood plate of 10 mm or more) of a
size that is big enough to take up the complete copper plate.


Step five
Bolt and clamps
You now have almost all the parts you need to make you throat plate (which
should
n't take long to make, I did mine in one evening)
The only thing you need is a bolt, (nothing fancy, dimensions I'll give
later) and a couple of clamps.

Step six
First production step Cutting the hole.
Take your copper plate and mark out the position of the hole. Centre pop it
and scribe a circle that is the size of your outside boiler barrel minus
twice the height of the flanges and a bit extra reduction for safety (2 to 5
mm will be good) When your at it, also scribe a circle that had the outside
boiler diameter size.
Cut out this hole. I used the boring head on my milling machine and made a
hole of about 75 mm if I remember correctly for a 106 mm outside boiler
barrel diameter.

Step seven
Beating the boiler flange. first stage
Anneal the copper plate. Take the steel ring and put it on your work bench.
Put the copper plate on top and try to align the hole with steel ring (i.e.
place the hole concentric above the ring..........no great accuracy is
needed, just take a good look)

Now gently start beating the plate inwards the ring with a steel hammer.
During this progress the plate and ring will shift a little bit, but by
in-between adjusting the position not much will go wrong. Do this for the
complete circumference, but do not try to beat the flange in one go. This is
wrong. First stage (before annealing again) you only will be able to beat
the flange in for about
20 or even 30 degrees.
After annealing you can maybe go as far as 45 degrees. This is far enough.
Do not go any further. Try to position the ring and hole as you go, but a
little shift, or unroundness of the hole isn't important yet.

Step eight
Beating the boiler flange. second and last stage
Anneal the copper again.
Take the surface plate. Put it on your workbench. Put the annealed copper
plate on it, with the flanged part facing up-wards. Put the ring over the
partly formed flange and try to locate it a good as you can (by vision only
should be sufficient). Now use the clamps to fix the ring on the copper and
that in its turn on the surface plate on your bench.
(I used a 10 mm steel plate, which I clamped on the table of my milling
machine, holding the ring, copper plate and surface plate (that was needed
so I would damage my table) in one go, firmly in position for the last step
of forming the flange.)
Once this set up is made, take the steel disk, put it inside the hole on the
surface plate and start shifting it around. Use it like a hammer by sliding
it on the surface plate and hitting the copper flange. This will now come up
right (work on the whole circumference, not just on one spot) and will
eventually touch the inside of the ring. (maybe another annealing step is
needed)
Because the steel disk is in contact with the surface plate, while swung
around, the edges of the flange will turn out 'square up' (so a nice flange
for taking up the boiler on the outside)

Step nine
Checking
You now should have a copper (flat) plate with a flanged hole in it. This
should take up the boiler barrel. If not (to small), measure the inside
diameter of the copper flange, and open out the diameter of the steel ring
accordingly (for instance, boiler barrel 106, but your flange turned out to
be 105.6. Turn the steel ring than 0.4 mm bigger than it was) Position the
whole lot once more and clamp it on your bench (after annealing) and give it
another treatment with the steel disk.
When done, cut the flange height to the desired dimension (i.e. 10 mm) with
a file or as I did with an angle grinder.

Step ten
Take the disk (of step three)
Chuck it in your lathe, drill a hole in the centre to take up the bolt (I
did use a M6 bolt) and turn a stepped 'reversed' flange to it.(so remove
material form the original diameter of a length.........don't know how to
describe this in English but I hope you understand what I mean). This
stepped flange will have a diameter that is the same as the outside of the
boiler barrel ( so it will fit nicely in the flange) and is just as 'long'
as the height of the copper flange + the thickness of your plate. (in my case
this step was round 106 x 10+3 long mm. The disk was round 112 x 20 thick,
with this 106 x 13 turned out............you understand??) (112? that's 106
+ twice material thickness.......read on and you'll see)

Step eleven
(almost there) Locate hole.
Locate on the made former plate (as described in step one) the centre of the
boiler barrel. Drill and tap a hole there to take up your bolt.

Step twelve
Put the copper plate (with flanged hole) on the former. Place the disk
inside the hole and bolt it to the former. Now you see why this stepped
flange on the disk is important. It will locate and hold the copper plate in
position and pressed down on the former during the next stage.
Now put the steel ring over the flange once more. Because the disk outside
diameter is 112 you'll find that the steel ring will slip over the disk
nicely.

Step thirteen
After annealing you can now start working on the outside flange in the usual
way (I presume you formed boiler plates before...... if not.......follow the
words and music of LBSC in his book of the Mona.......Great locomotive by
the way..... drive mine regularly)

Step fourteen.
During the beating process, the flange that is already
formed tries to move away. In this case however care is taken for that by
'locking it up' between the disk and ring. By bolting the disk to the
former, you're sure that every thing will be nicely lined up and stay in
position during the final flanging process. (of course extra annealing is
necessary as usual)


Hope this describes the process and is of any use. The photo's show
the throat plate and the formers and disks used.

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Part 1     Part 2     Part 3     Part 4

 


Flanging the throat plate  on this page


 GWR 14xx class loco on 5" gauge  and gauge 1  Royal Scot  class loco at our anual Model Engineer Exhibiton at Raamsdonkveer  14 March 2004