GWMark Posted February 26, 2014 Share Posted February 26, 2014 I recently bought a London Road Models RSU and today got the probe set for it. So my job tonight was to prepare the carbon rod for the probe and put a return plate together. However I have a question about the probe and carbon rod, when I inserted the carbon rod to measure how much I needed to cut off I was surprised by how easily it slide in. So I experimented with the collet to see how firmly the rod was held in. No matter what I tried the rod would come out very easily. This surprised me as I expected it to be firmly held in place so that it would make a good contact. Is this normal or do I have a problem? I read in the instructions that the rod should be cleaned with fine grade emery cloth or the like, but the will fine the rod even more and making it less firmly held I would assume. If anybody has one of these units I would be grateful to hear if this is anything to be concerned about or if I am missing anything. Thanks in advance Mark Link to post Share on other sites More sharing options...
RMweb Premium macgeordie Posted February 26, 2014 RMweb Premium Share Posted February 26, 2014 I've been using one of these units for a while and the carbon rods I have (bought from Eileens Emporium) have a very thin covering of copper film, similar to kitchen foil and they fit the collet well. There are different diameters available so it is possible you have the wrong one. I would suggest the simplest solution is to wrap a bit of aluminium kitchen foil around the rod you have so it is a tighter fit in the collett. With regards to a return plate, I never bothered making one for mine, I just use a strong crocodile clip and I have never had any bother with it at all. If you are modelling in one of the larger scales it probably is worth the effort, but as I model in 4mm I didn't think it was worth bothering, it's just something else you have to find a storage place for. Ian Link to post Share on other sites More sharing options...
JeffP Posted February 27, 2014 Share Posted February 27, 2014 Yes, you need a decent connection at the rod, or you will get localised heating there. The aluminium foil idea above sounds good to me. Link to post Share on other sites More sharing options...
Paul Cram Posted February 27, 2014 Share Posted February 27, 2014 If you turn the brass securing collar round and screw on that way it should tighten. Link to post Share on other sites More sharing options...
Jol Wilkinson Posted February 27, 2014 Share Posted February 27, 2014 I've been using one of these units for a while and the carbon rods I have (bought from Eileens Emporium) have a very thin covering of copper film, similar to kitchen foil and they fit the collet well. There are different diameters available so it is possible you have the wrong one. I would suggest the simplest solution is to wrap a bit of aluminium kitchen foil around the rod you have so it is a tighter fit in the collett. With regards to a return plate, I never bothered making one for mine, I just use a strong crocodile clip and I have never had any bother with it at all. If you are modelling in one of the larger scales it probably is worth the effort, but as I model in 4mm I didn't think it was worth bothering, it's just something else you have to find a storage place for. Ian Using a croc clip was the suggested method when RSUs first appeared on the scene in the UK. However experience has shown that it isn't the best way, as the pointed teeth are actually points of high resistance. I use and recommend a steel baseplate. Otherwise arrange some positive connection with a good contact area such as bolting the return lead to the model with an eyelet terminal. Less resistance throughout the circuit means more "power" at the probe end. Jol Link to post Share on other sites More sharing options...
RMweb Premium Siberian Snooper Posted February 27, 2014 RMweb Premium Share Posted February 27, 2014 The 6mm dia carbon rod is what you need for the probe. For the earth I have an earth plate and I also use one of those aluminium hair clips sold by hairdressing suppliers about £9 for 70 or 80, a lot cheaper than half a dozen for a fiver from some model suppliers. They are also good for clamping things together and you can bend them to suit. Happy Zapping SS Link to post Share on other sites More sharing options...
halfwit Posted February 27, 2014 Share Posted February 27, 2014 As has been said above, the collet has a tapered brass locking collar which when pushed down the collet should hold the rod firmly in place. I also have a LRM unit (seen here) and have never experienced problems with the probe (or with any other part of it. Good quality kit). I use a coil type soldering iron stand to keep the probe in when not in use. Helps keep it cool and stops it rolling around the bench. Currently in use on a pair of Roxey Mouldings ICI wagons. Link to post Share on other sites More sharing options...
GWMark Posted February 28, 2014 Author Share Posted February 28, 2014 Thanks everybody. The foil trick did the job. I did a few test joints last night and plan to have a fuller play with it tonight. I have a steel sheet as a return plate, local metal working shop let me have it for a donation to the tea fund. Looking forward to having a good go with it, I have an old brass kit of a wagon that I picked up cheap, with all the overlay it has it looks like a good candidate to try and not a big problem if I really mess up. Thanks again Mark Link to post Share on other sites More sharing options...
Kenton Posted February 28, 2014 Share Posted February 28, 2014 It is a wonderful bit of kit that you will come to love and start to shun the old soldering iron (though it still has its place) Min is a Grasskop one (possibly the last) rather than the LRM one though the design is very similar. Get yourself some strong magnets and learn how to use card to insulate work electrically. It is amazing how low a setting can be used to vapourise brass when only a small area is in contact. Remember a steel plate is a massive heat conductor, the temptation is to simply turn up the power but you will find that you get through probes at a heck of a rate. I often use the crocodile connector for the earth as by placing that in a suitably hidden place on a kit again there is nowhere else for the current to flow but the join at the probe end. But the clip must be kept clean - as always rule 1 of soldering. I have also used aluminium foil to tighten the probe in the collet. Though most of them have been a tight enough fit. Don't forget to keep the point of the probe sharp using a pencil sharpener. Link to post Share on other sites More sharing options...
GWMark Posted March 1, 2014 Author Share Posted March 1, 2014 I broke out an old kit I picked up cheap on a second hand stall to have a go with the RSU tonight. The result, I'm completely sold. With very little practice I got the sort of results that would have been impossible with a conventional iron. I could not resist taking a photo, sorry about the poor quality... The nice clean joints and the lack of the need to do any cleaning up post making the joint are just great. The kit itself is an old Spratt & Winkle kit of an LSWR 8 ton cattle wagon. I would have gone further, but I need to find a picture of the original to get a better idea of the positioning of the rivet strip overlays for the hinges etc. Still a lot to learn about using the RSU, but from what I have seen so far I think this is a purchase (or actually a present from my wife) I will not regret. Mark Link to post Share on other sites More sharing options...
chrisf Posted March 1, 2014 Share Posted March 1, 2014 Using a base plate and a selection of magnets to hold the work frees up more hands than the good lord gave us! I was fortunate to have one made for me. It consists of a piece of MDF to which is fixed a relatively thin piece of steel. To it are bolted two lengths of steel 90 degree angle. Squires sell magnets - I use three different sizes. Chris Link to post Share on other sites More sharing options...
JeffP Posted March 2, 2014 Share Posted March 2, 2014 At Kettering yesterday my son, a welder by trade and now studying Mech Eng at Loughborough, saw a set of RSU probes on the Squires stand and wanted to know what they were for. He reckons they look like solid carbon rods he's used to burn out/lift welds. He also reckons those might come in 6m or thereabouts....... We are going to check today. Link to post Share on other sites More sharing options...
Killybegs Posted March 4, 2014 Share Posted March 4, 2014 Having a crocodile clip does give a flexibility. You can hold two very small parts together in a pair of pliers and attach the crocodile clip to the pliers. Alternatively you can clip it onto your vice - see pics below: Link to post Share on other sites More sharing options...
JeffP Posted March 4, 2014 Share Posted March 4, 2014 At Kettering yesterday my son, a welder by trade and now studying Mech Eng at Loughborough, saw a set of RSU probes on the Squires stand and wanted to know what they were for. He reckons they look like solid carbon rods he's used to burn out/lift welds. He also reckons those might come in 6m or thereabouts....... We are going to check today. Found out you can get a box of 50, 6.4mm rods for reasonable......certainly less than £0.50 a rod. They are called arc gouging rods, or air-arc gouging rods, and come in various sizes. Link to post Share on other sites More sharing options...
Kenton Posted March 4, 2014 Share Posted March 4, 2014 arc gouging rodsSounds like a fair description of what happens when the RSU is set too high and the probe is lightly touched on the brass. I have knocked holes in sheet brass and vapourised brass wire by careless action. As for catching the metal of the probe on the kit as you insert the probe into a corner of a box - sparks fly! Link to post Share on other sites More sharing options...
JeffP Posted March 4, 2014 Share Posted March 4, 2014 My Mark says you can gouge out a complete weld with enough amps and a thick enough rod, say 30mm, so I'm not surprised. Link to post Share on other sites More sharing options...
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