Silver-soldering loco construction

Discussion in 'Techniques' started by Giles, 26 July 2015.

  1. Giles

    Giles Western Thunderer

    On my last couple of builds, I have remembered my youth, and gone back to silver-soldering wherever possible, instead of the more usual soft soldering. The easy availability of silver-solder pastes (in syringes) and small torches makes this so much easier and more viable. To be frank, I find it very much easier to get a clean, good job this way than I do witth sft soldering now.

    The silver solder pastes tend to hold the job in position during heating, and, if used sensibly, deposite very little extra solder on the job - which spreads in a very thin layer, and usually requires no cleaning off. I have a jar of 'pickle' and an ultrasonic cleaner, and thats about it.

    At the moment, I'm two-thirds of the way through an 0-14 Kerr Stuart Wrenn - which makes for a very small loco, and only the boiler barrel is soft soldered. Even the backhead and all its fittings are silver-soldered. The industrial Garratt I built recently had all its valve gear Silver-soldered.

    it is a surprisingly easy process, and can be very delicate indeed. From our point of view it also enables the further soldering of items ( both silver soldered and then soft soldered) without the whole thing falling apart.


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  2. Giles

    Giles Western Thunderer

    The Garratt has silver soldered valve gear (nickel-silver laminations) and silver soldered cylinder end-cover/slidebar assemblies

    P A D, AdeMoore, Len Cattley and 17 others like this.
  3. mickoo

    mickoo Western Thunderer

    That's a nice looking beastie :thumbs: and welcome to the mad house :thumbs:
  4. adrian

    adrian Flying Squad

    Very nicely done. I do like silver-soldering but I have only used it for building up small detailing parts, that way when I soft solder it to the loco there's no danger of it falling to bits. To take it to the extent you have is impressive - I baulked at silver soldering plate work, worried that I might distort the thin sheet with the heat.
  5. 40126

    40126 Western Thunderer

    Welcome Giles :thumbs:

    Steve :cool:
  6. simon.bolton

    simon.bolton Active Member

    Hi Giles, lovely work! What solder paste do you use? And would you mind explaining the process in a little more detail?

  7. Giles

    Giles Western Thunderer

    Hi Simon,

    I use the 'easy' pastes shown in this link below - the temperature range is 680 to about 730 degrees C. I don't bother with the harder ones, as we have the option of going down to soft solders. Solder Paste 30g Easy, Syringe&queryFromSuggest=true

    The process is lovely and easy - applicable to brass, nickel-silver, copper, steel and many other metals.
    As always, clean the metal (I usually use fine wet-and-dry, or a fibreglass pencil), and then apply a small amount of paste to the joint (or both pieces, if sweating two pieces together), making sure that the paste is 'smeared' on. The paste contains both the silver solder and the flux, so it is vital that the metal to be soldered has a smear of the paste over it, otherwise it will oxidise, and the solder won't flow.

    I have a couple of soldering blocks, which are heat reflecting bricks (about £5 each). Make sure your work piece is set up nicely on somthing fire-proof like this, and using a small torch, heat the joint up with the tip of the blue cone of the flame. Watch carefully, and you'll see the flux dry, and change, and then just before the brass gets to dull red, you'll see the silver-solder flash to liquid and flow. You can move the flame around to encourage the solder to follow.
    Note, you've got to complete the heating in one go. If you half-heat it, stop, allowing it to cool and then have another go, it won't work, and you'll need to clean it off and reapply more solder to clean metal and do it again..

    You'll get a quick strong job, with very little excess solder. It's also extremely good for small details (think jewellers here...)

    I did a (terrible) video in an effort to be helpful and informative

    - Video Tube for YouTube - iPhone/iPad
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  8. Dikitriki

    Dikitriki Flying Squad

    Excellent video, Giles. Thank you for taking the time to prepare it.

    It would never have occured to me in a million years that valve gear could be silver soldered. I'm not saying I will use it on valve gear, but I can see whole new possibilities in fabricating sub-units, and you have certainly demystified the process:thumbs:

  9. Giles

    Giles Western Thunderer

    Bless you Richard - it's a fun, easy and increadibly useful process.

    I have just a moment ago silver soldered a Class 37 step - an etch from Pete Harvey using exactly the process described - and this is it, with absolutely no cleaning up whatsoever.

    Stirling O and AdeMoore like this.
  10. adrian

    adrian Flying Squad

    Agreed - it is easy to do and another useful technique for the toolbox. Although I still use the "old-fashioned" method of little pallets of silver solder rather than solder paste. It does mean you have to be careful to ensure a close joint but it's great to see the solder flash through the joint and as you say no cleaning up afterwards. Well no solder to remove - I still clean the component by dropping it in an acid bath for an hour or so.

    The point you make about heating the job in one go is worth re-iterating. This is one of the things that makes it useful for adding new details in that it is possible to solder more detail without disturbing the previous joint.
    AdeMoore likes this.
  11. Giles

    Giles Western Thunderer

    Sticking out like a sore thumb at the moment are the completed steps -one of the most delicate silver soldering jobs I've done (the brass hangers are about 0.8mm x 0.5mm).
    The only point worth mentioning, is that when silver soldering things this fine, you can melt the brass into a blob if you're not careful, so the technique is to dance the flame on and off it, not allowing the brass to get too hot (if it gets to a bright red, then it will disappear....). I wouldn't do these steps as your very first SSoldering piece, but once one becomes practiced, it certainly becomes the preferred way of doing it - simply because previous joints don't fall apart when you make the next one.
    One the steps, no cleaning up was necessary at all, other than routine 'pickling'. I use Swimming Pool PH reducer (in water) as a very effective pickle.

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  12. simon.bolton

    simon.bolton Active Member

    Hi Giles: that's fantastic. I've been keen to have a go at silver soldering for ages and you've just provided all the information and inspiration I need! I'll have a go and let you know. Incidentally, do you not need any sort of barrier to prevent the solder flashing into unwanted joints or does it normally just stop as you show at the end of your splendid video?

    Many thanks.
  13. simond

    simond Western Thunderer

    Really very nice.

    I will have a go. Thanks for the link & the inspiration!
  14. Giles

    Giles Western Thunderer

    Hi Simon - under normal circumstances, the silver solder will only go where the flux is (has been). When I an doing articulated joints in the valve gear, I am careful only to use a very small amount of paste, and apply it from the outside, applying heat quickly so it doesn't get the chance or encouraged to flow anywhere I don't want it. Of course you can always 'dirty' any metal you don't want to solder, either by heat or chemicals, or use heat sinks.

    There's no substitute for a bit of practice on some scrap, either!

    Simon - it would be great to see people give it a go - let us know how you get on!
  15. simon.bolton

    simon.bolton Active Member

    Hi Giles, solder and bricks on order and revving up the blow torch!
    Giles likes this.
  16. Mr Grumpy

    Mr Grumpy Western Thunderer

    Hi Giles,
    Thanks for a very enjoyable and informative explanation of silver soldering. Loved the video, I would not have believed you could solder such minuscule parts without distortion or obliteration!!
    Like many others, I would not have considered this medium for building etched kits.
    In my previous working life, I regularly soldered pipe work with a blow torch. Somewhere I have an old meths torch which had an extremely fine flame cone and would have been ideal for this application. The intensity of the flame was increased by blowing in to a fine rubber tube to increase the primary air to the gas.
    Back to the present, I really am interested in taking this up, please could you give some info on the type of torch you use/recommend?
    Once my present project is complete, I will nip out and buy a nice MMP wagon to practice on!!
  17. adrian

    adrian Flying Squad

    This is one reason I try to make as much as possible with nickel-silver rather than brass as it has a higher melting point so less likely to end up with a blob.

    As you say plenty of practice on a few scraps will pay dividends.

    I've just remembered a long ago failed blog posting on RMWeb about silver soldering. I was trying to make some lamp irons which wouldn't fall apart when soft soldering to the loco

    It's just a couple of scrap pieces of nickel-silver so would be a very simple test piece for people to try.

    Finally as for pickling - I can't remember where I got it from now but I have a 2litre bottle of 96% commercial sulphuric acid. You probably wouldn't be allowed to buy it now - needless to say it is securely locked away and treated with utmost respect.
  18. Giles

    Giles Western Thunderer

    Last edited: 4 August 2015
  19. Giles

    Giles Western Thunderer

  20. mickoo

    mickoo Western Thunderer

    Giles, what sort of flame tip do you get with these items, quite a few guys here are using micro flames for soldering and I'm keen to try that on the next project, basically tired of cleaning up the work, most of which is the tinning off the soldering iron tip used to transfer the heat as opposed to solder from the joint.

    So, I'm ideally looking for one with a pencil tip to the flame as opposed to a broad flamer thrower effect you often get.

    Several guys here use the Iroda solder pro 120

    or the Nimrod 100

    but they are more expensive, cost isnt an issue if they do exactly what I want, but having used similar items at work the flame tip is often not clearly defined and pointed.

    PS the links worked fine for me :thumbs: