jdowning - 5-3-2008 at 12:45 PM
A recent electrical power surge "fried" an ultra violet sterilising unit that we having been using for household water treatment (our water supply is
from a private well). To refurbish the unit would have cost more than a new steriliser so a new unit was installed and the old unit was added to my
scrap collection of 'useful' materials.
The body of the steriliser is made from thin walled stainless steel tubing 2 1/2 inches (64 mm) in diameter. I thought that this might be the basis
of a new bending iron - made from scrap materials.
The heating element for the bending iron is to be an old 150 watt heavy duty soldering iron that I picked up at a local garage sale for a few
dollars.
If there is a need for temperature control a used 600 watt light dimmer should serve - fitted into the rather nice aluminium casing that held the
ballast and electronics of the old steriliser unit. This may not be necessary, however.
jdowning - 5-3-2008 at 01:47 PM
The body of the bending iron was made by cutting a length measuring 8 inches (203 mm) from one end of the steriliser unit (another bending iron could
be made from the other end).
Two slots were cut and filed at the open end - measuring 1.7 mm and 2.5 mm in width. These slots are for bending the purfling or filet strips glued
between the rib joints of a bowl - the slots provide additional support (and heating area) for the strips during bending. A piece of tube measuring
about 30 mm in length, with a quarter section removed, was sprung into the interior of the bending iron to provide a backing surface for the slots.
jdowning - 5-3-2008 at 02:01 PM
The wooden handle was removed from the soldering iron (it was just a tight push fit on the shank of the iron) and the electrical cord disconnected.
This was in poor condition and was two wire without a ground so will be replaced with a three wire grounded cord for safety.
The heating element is supported centrally withing the bending iron tube with a clip - formed from a 25 mm wide strip of thin stainless steel - sprung
into place.
For safety, the electrical connections are contained within a blue plastic junction box taken from the original steriliser unit. This is mounted on a
wooden disc that is a tight press fit on the shank of the soldering iron - like the original handle of the iron.
Spacer tubes fitted over the shank of the iron ensure the correct longitudinal location of the heating unit within the bending iron.
jdowning - 5-3-2008 at 02:22 PM
A stand for the assembled bending iron was made from standard screwed iron plumbing fittings available from any hardware store. This is attached to
the original water supply connection of the steriliser unit (very convenient!). The bending iron may be screwed to a bench or fixed to a block of wood
and temporarily clamped to a bench.
All that now remains is to wire up the unit and test it.
While it is doubtful if anyone has a steriliser unit or soldering iron exactly like this from which to make a similar conversion, this is just to
present a few ideas about the possibilities of making a bending iron from scrap materials.
It should be pointed out that a fancy bending iron is not absolutely necessary for hot bending the thin ribs of an oud or lute bowl - an open flame of
a spirit lamp (alcohol burner), a radiant electric fire or hot air electric paint stripper can all be used as heat sources (with care) to bend ribs.
jdowning - 5-4-2008 at 11:56 AM
After completing the wiring some quick tests were made dry bending some yew 1 mm thick and purfling measuring 2mm wide by 2mm deep. I was particularly
interested in how the purfling would bend using the slots in the bending iron to control the work. Both tests were successful with tight curves of 80
mm diameter being easily made.
The iron was quite slow to warm up to temperature but eventually reached an equilibrium state just sufficient to lightly scorch the wood. Raising the
heating element within the bending iron tube would likely speed up the heating of the upper surface. Temperature control should be unnecessary.
OudandTabla - 5-4-2008 at 07:43 PM
Nice reuse of materials. It looks like a pretty functional unit. Was the scorching occurring with the unit turned all the way up, or did oyu mean the
equilibrium of some lower temp?
DaveH - 5-5-2008 at 08:58 AM
Interesting. I was getting a bit concerned seeing the two pin plug in the photo until I read that you'd replaced it. I think earthing this thing is
probably a good move. 
jdowning - 5-5-2008 at 02:14 PM
Josh - the scorching occurred with the unit fully heated up to an equilibrium state (it took quite a while to reach this condition). With this design
there will be a temperature gradient along the length of the bending iron heated surface - hottest immediately above the heating element, cooling off
towards the extremities of the heated tube. It is a matter of choosing the best location on the iron surface to do the job, based on experience -
avoids getting into a complication of electrical temperature control.
Also, temperature can be physically controlled by raising or lowering the heating element position within the bending iron tube.
I test the temperature by touching the surface with a wet finger tip and look for instant conversion of water to steam - sounds like a micro explosion
or 'splat'. A 'sissle' is not hot enough. I then usually wipe the wood with a damp cloth prior to bending as this helps the bending process and avoids
any scorching - although some scorching is not detrimental. I never soak the wood prior to bending.
DaveH - the two wire electrical cord is 1950's standard and as the heat insulation of the wire looked suspiciously like asbestos fibre it had to go.
Grounding (or earthing in the UK) is essential. The original soldering iron relied upon the wooden handle for electrical insulation (early double
insulation standard!) - but not good, even with the North American voltage standard of 120 volts - even worse with British 220 volt standard. So,
better safe than sorry when dealing with electrical systems.
OudandTabla - 5-5-2008 at 07:17 PM
Great, thanks for the information. I am looking to build myself a 'new and improved' heat pipe, so this is excellent food for thought. I really
appreciate the ideas and pictures.