There appears to be some confusion about RSU's and how to use them. The following notes are based on my experiences in using one for a number of years. The ideas for the base plate and magnets are based upon methods expounded by the late, lamented, Bernard Weller.
A good many years ago I was at Telford and saw the London Road Models RSU demonstrated by the man himself (this was before it went to Fourtrack). I was sold on it and ordered one on the spot. I now rarely use a conventional soldering iron, usually for laminated etched rods held in the vice, but there are ways to avoid that too by turning the vice into the negative terminal.
How does it work? The box is simply a transformer with several output windings that produce - in this case - voltages 1, 1.5, 2, 3 & 4.5. However, it does so at very high amperages, in the order of 40 amps for the highest settings. The power is controlled by a foot switch.
The negative terminal is attached to a base plate on which the items to be soldered sit and the positive to a carbon probe. When the probe is placed upon the work piece, it produces a high temperature almost instantaneously but very localised. Used with a foot switch it is easily possible to hold the items to joined down on the plate with the probe and apply heat using the foot switch. If one has solder cream between the parts it melts very rapidly and joins the parts. As soon as the solder has flashed silver, switch off the power, still holding the probe. With good quality solder cream, the joint will 'go off' in seconds and the joint will be strong.
It is not difficult to produce joints that have almost no solder showing,
making cleaning up an easy task.Cleanliness
is very important and it is critical that no power is lost in the chain from
the unit to the work piece, so electrical joints must be tight. Here
you can see that the plugs that go into the unit are cleaned to a bright
shine. It is important too to keep the springs opened out to ensure a
tight fit in the socket.Back to top
The negative plate for my RSU is a steel plate fixed to a piece of MDF. A bolt is passed through so that the heavy brass tag with the negative lead firmly soldered to it can be bolted tightly to the steel plate. Notice that all metal is bright but before clamping together, I smear a thin coat of Vaseline on the terminal.
The tag is then bolted down as tightly as possible. The lead is soldered into a pre-drilled hole in the brass tag.
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I
strip the copper from a length of carbon rod, sharpen it in a pencil
sharpener and use a fibre glass brush on the remaining copper.
The rod is pushed well down the holder and the brass ferrule forced down hard so that there is no wobble in the probe at all.
I am going to edge solder two pieces of brass at right angles with a seam joint. To do this I need magnets to hold the work, a small engineer's square, 179° solder cream, 179° wire solder with 2% silver and flux.
The parts to joined are cleaned, including the back of the piece that will lie on the plate. It is important to ensure that there is as little resistance as possible in the path so that the probe will heat up properly. Back to top
The magnets hold the base down and the support upright, which is also kept vertical by the engineer's square. To this we add a few blobs of solder cream.
The magnets can be bought (for about £8 in 2010, minimum order 4) from http://www.magnetsales.co.uk/deep.htm and I highly recommend them as strongm convenient and safe (to big for kids to swallow and they don't look like sweets).
The cream is relatively expensive but one uses very little. I have
been quite generous here because I want the solder to run through the joint
later too.Back to top
Here the probe is in action and set at 3 volts. The tip must touch
both pieces of the work and the heat is kept on only long enough for the
solder to adhere to both pieces. Once this is done - it takes seconds
- let it cool, remove the magnets and check for square. Now I set it
up again on the plate to finish the seam joint.
Once the work is securely set up again, I run a generous dollop of flux
along the whole of the joint area.
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Now the solder blobs are re-melted and they will run into the length of the
joint. I simply run the probe gently along, not too fast. One
can go over it several times if necessary.You can see now how the solder has run along the joint and the back of the joint is clean and neat. For some joints this will be enough but often it will need to have a strengthening fillet added.
To
add a fillet I simply use the wire solder and run the probe along it and
into the joint. The silver in the solder ensures that it runs well and,
as with the solder cream, it 'goes-off' within seconds of the heat being
switched off.I hope that helps you get more from your RSU.
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