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Setting up my RSU.




Last year at ExpoEM North I treated myself to a London Road Models Resistance Soldering Unit. Yesterday I decided that it was about time that I set it up.

Opening the box reveals a big grey unit, a couple of leads, some carbon rod and a set of instructions. The big grey, rather heavy, unit has two leads coming out of the back, one with a mains plug on it and the other with a footswitch on the end. The two other leads plug into two of the four sockets on the front of the unit, different combinations giving different voltages. One of the leads, the red one, has a probe on the end and the other black lead is left bare for you to attach to your baseplate as you see fit. The carbon rod is to be shaped as desired and fitted into the probe, I chose to sharpen it in a pencil sharpener to produce a point. Here's the kit;




Not included is a baseplate which is left up to the purchaser to provide to suit their needs. The instructions suggest either mild steel plate or brass sheet. I used .064" brass from Eileens screwed to a piece of MDF with a bolt screwed into one corner for the black lead to attach to, the lead having an eyelet crimped onto it for that purpose (the black lead can be soldered in place instead);




How does it work? Well it uses 'the heat generated by passing a relatively large alternating current between two surfaces to be joined' to melt the solder and make the joint. The parts to be joined have to be pre-tinned (although solder paste can be used) using a conventional iron. The work is placed on the baseplate and the probe used to hold the part to be soldered in place, or placed adjacent to it, and the footswitch depressed to turn the unit on and provide the current. When the flux boils and the solder flows the footswitch can be released, leaving the probe on the job until after the solder has solidified. Taking away the probe before releasing the footswitch can result in arcing leaving unsightly marks on the workpiece. The power can be varied between 1 and 4.5v, although the highest setting will be far too powerfull for most 4mm work I feel.

Here's some scrap that I've been playing with, Ive been using some aluminimum kitchen foil between the work and the baseplate as sugested in the instructions to save the baseplate from getting covered in flux;




I'm quite pleased with it so far, the real test of course will be using it on a kit. I've bought this for adding detail and overlays to etched kits, not as a replacement for my trusty Antex or for assembling frames etc. The advantage for detail work will be having the heat localised, which means that nearby joints shouldn't come unsoldered, and that the probe can be used to hold the part to be added in place. Which has to be better than holding, for example, a bonnet catch in place with a cocktail stick whilst bringing an iron to it...



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Once you get used to it you will be surprised how much you use it!


Good luck and happy soldering.rolleyes.gif



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First time I have seen one of the LRM units. I must say there are not as many options as with the Ganderton RSU that I have - but I expect it will do as good a job.


I will caution about sharpening to a point the carbon tip. I just did mine again today (just like a well used pencil it blunts itself) but the finer the point the more current is localised at the tip and you really do need to "plug" it down a setting (or two) - I forgot and vapourised the part I was adding :(


Brass plate is not the best option either. You will soon see why after a while when you start soldering parts to it as well as each other !! Steel plate is very difficult to solder to and although seems less conductive it functions well. The other really big disadvantage is that brass does not 'take' magnets. Magnets and RSUs go together along with card insulators really well and work so much better than wood blocks. You can insulate parts (away from that massive heat sink) on the card and then use a magnet to provide a bridge of conductivity back to the plate. It means that a lower setting can be used.


Best used with solder cream - I now use that for most work - you require so little that cleaning up afterwards is so much easier.


Getting into the habit of turning off before removing the tip is a bit of a challenge, also you have to try to think of the shaft of the iron as being surrounded by white metal - touch any part on the work piece other than the carbon tip and sparks will fly !


Too high a setting and you are into arc welding - mine will happily knock a hole straight through brass sheet.

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Hi 'Halfwit' (?) -


Kentons in teaching mode again - and well-worth listening-to. I did a similar blog entry some time ago - and having been corrected by Kenton on several points (particularly using insulating material - I actually use asbestosised paper- under the working point) I've found it a very useful tool.


Another suggestion is to bolt a piece of angle to the work-plate. Useful for frame assembly etc. Again, not my idea - I saw it demonstrated at ExpoEM South a couple of years ago.





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As I had mine switched on and was attempting what would be near impossible (ok, just difficult) with a normal soldering iron ...



A 0.6mm x 3mm length of wire soldered flat end-on onto an etched gear lever (no hole etched for the wire as the gear lever is only 0.4mm.


The gear lever held in place on the plate with a magnet a tiny dot of solder paste, file the end of the wire flat and dip in flux, holding the wire with fine tweezers place end-on in solder cream dot, apply carbon electrode to wire on a low setting wait for phizz and switch off. All done - not for those of nervous disposition :lol:


It is another one of those fairly expensive tools that when you finally get round to purchasing - and using ;) - you wonder how you managed without it.

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I'll go along with everything Kenton said. When I've demonstrated/let others have a go at using my PSU at the SWAG do at Taunton over that last couple of years people have been amazed at how simple it really is (although I could never pin Andy Y down to have a go!).


No need to tin using a conventional iron unless you are sweating something on. Also, solder paste is expensive and difficult to find when using a step soldering technique with differing melting points. Ordinary solder, cut into short (ie a couple of mil or less, only enough to make the joint) lengths, placed in position on the cleaned and fluxed joint and held down by the carbon probe so that the current passes through the solder into the metal will do just as well and I find is is much more controllable.


Can't be at Taunton this year - I'm going to get withdrawal symptoms.



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I have soldered a second wire to my baseplate, ending in a crocodile clip. I rarely use the baseplate any more.



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Thanks for all the comments. I'll persevere with my brass plate for the time being, hopefully using alluminimum kitchen foil between the work and the baseplate will prevent me from soldering the work to the baseplate... :blink:


There is still a lot of playing with the unit to be done, trying different solders for example, however I can allready see lots of uses for it.



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I would certainly agree with Kenton that steel is a better baseplate than brass. A chance conversation with Barrie Fitch at Expo South led to him doing me the great kindness of making a baseplate for me, complete with angle iron. A selection of magnets from the ever helpful Squires completes the setup and gives me the equivalent of a few more hands!


IMHO you have done the hardest thing with your RSU and that is deciding to buy one. I am still exploring just what mine [also from London Road] will do, coming from the standpoint that it should be used for most tasks except where a conventional iron is the only sensible option.



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Chris, the more that I think about it the more I feel that a steel baseplate would be better.

What thickness of steel do people use, or is it a case of whatever you can get? I was once in a position where getting hold of steel was easy, now a change of location and career means that I'll probably have to pay for some...



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Sorry for digging up an ancient post, What size is your baseplate? Just going off a rough scaling from the screen, I'm guestimating around 12" x5"?

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