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Old 21-09-2005, 02:46 PM   #1
DX-SFX
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Default Confusion over solder

Some people seem a little confused over different types of solder. There are two basic types. Soft solder and hard solder. Hard soldering is more allied to brazing and the term is not heard very much.

Soft solder is almost invariably at the low end of the temperature scale, typically around the 180-190 degree C mark. The two types that will be encountered the most are the common tin/lead alloys used for electrical work and the newer almost pure tin versions designed for modern plumbing. Either can be used for building an Eagle and are easily available at most DIY stores. Both are easy to use (a lot easier with a good flux) and can be heated with simple gas torches also easily sourced from DIY stores. I'd recommend a fine flame tip to go with the torch mind you.

The most common form of hard soldering the average person is likely to encounter is "silver solder". This is seriously strong stuff but requires a much higher temperature, typically between 630 to 700+ degrees C depending on the alloy. It's imperative to use the recommended flux as at these temperatures, the surface of the metal oxidises very quickly (it's just below the point where brass starts to glow red). It has it's uses when joints have to be bullet proof such as making the clamps that hold the CM in place but otherwise I can't recommend it for putting a frame together due to the distortion the extremes of temperature introduce into the structure. I did it once but never again.

Silver solder is so named because it contains a small proportion of silver so as you can imagine, it costs quite a bit more. It's also best to avoid the silver solder wire that comes pre-coated with a hard flux. It tends to flake off and is not as versatile. It's far better to mix up some of the appropriate flux powder into a paste and apply it to the joint in advance of applying any silver solder. AG1 and AG2 are the preferred silver solders to use although there are some cadmium free alternatives for those who worry about such things.

However 98% of the joints on an Eagle will be soft soldered. To get excellent strong soft soldered joints, a couple of things are worth bearing in mind. Firstly, make sure the metal is as clean as possible. Asking the flux and solder to penetrate a crust of crud is not going to help. Secondly, use a good flux. I've bleated on about this but once tried, you'll never go back. Ignore the "Multicore" solders with flux in them. This flux is too gentle as it's designed to not obliterate delicate and spotlessly clean electronic components (although the actual solder in itself is fine). Get yourself a tub of the flux plumbers use to sweat the joints of copper water pipes. A good brand in the UK is Powerflow Flux which comes in a yellow plastic tub. It can be used on tin/lead solders or pure tin plumber's solder. It's formed of various powdered flux salts in a paste and can be applied with a cheap small modellers paint brush. What flux does when it's heated is eat it's way through any oxidation on the surface allowing the solder to alloy itself with the underlying metal. Because it's basically acidic, it's essential to remove it with cigarette lighter fluid or cellulose thinners once the joint is made otherwise a few weeks down the line, you'll start to get little pale green blooms on your frame. Ignore any directions that say it can stay on the joint. That's nonsense. Besides, any sticky flux left on the joints will quickly clog anything we use to dress the joints subsequently like rat tail files. There is an alternative flux that usually comes in a tin and looks a bit like toffee coloured car grease. In my experience this is not as effective or tenacious as the cream coloured Powerflow type and although usable, I definitely prefer the latter. There is a third type often referred to as "Bakers Fluid" and this is very good except that it looks like water and beads like water so it can be awkward to put and keep in the place you want it.

To control the amount of solder each joint takes, I precut short lengths of solder and place them on the prefluxed joint. Gentle heating with the gas torch will see the solder go molten (it suddenly goes more chromey in appearance) and it should flash around the joint in a second or two. If the solder beads up but doesn't flash, it's because the joint isn't hot enough but as soon as the joint reaches temperature, the solder should suddenly flow. There's no reason you can't feed the solder in by hand but using small precut lengths makes it easier to gauge how much solder has gone in, nearly always results in a neater joint and most importantly, gives you a free hand to manipulate things.

Another common question is "won't adding more pieces merely make what I've already done fall apart?"

Yes, if you keep the heat source on the joint, however that's a good thing if you want to make corrections. In practice though it takes more heat to melt a joint than it took to form it. That's because the solder has alloyed with the brass and it's now a tin/lead/brass (copper and zinc) alloy. The chromey appearance I mentioned earlier is also our friend. You can see how much a joint has re-melted by the appearance of the solder and indeed it's very easy to gauge just how far the heat is travelling. You soon pick up a feel for it and I can only urge that a little bit of experimentation to show how easy it can be.

Finally, for the solder to penetrate the joint, there has to be a gap to penetrate into. Parts that are clamped too tightly together won't let the solder penetrate. I mention that purely as a point of interest. In practice I doubt if any of us can produce the parts with the accuracy that a precision engineer could so this is not generally a problem. It is worth mentioning that making the parts a "good" fit will make a difference. The strongest soft soldered joints are made where there's a gap of one or two thou. Even quite large gaps can be filled neatly by the natural filleting action of the solder so there's no need to panic if things go slightly askew.

Just a quick word about solder paste. This is granulated solder premixed into a flux that can be applied by brush to a joint. I know several people who swear by it and I'd never say don't experiment with it but I'm not convinced it's as strong. I've tried a couple of brands and both seem to cook rather too easily in a flame but that might just be me. There's no reason at all why it shouldn't be as good but personally I'm far more confident of a strong joint with the separate flux and solder. As always, it's best to experiment a bit and use a method you feel most comfortable with.

(Edited for multiple typo's)
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Old 21-09-2005, 03:01 PM   #2
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Chris,

Short of starting from scratch, do you have any recommendations for quickly cleaning up soldered joints (i.e. AB Models 44" Eagle) that have obviously had far too much solder applied.

Don't fancy ruining all my files by manually filing all the crud away around the joints...though having said that there are a couple of pieces that I will need to re-position...
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Old 21-09-2005, 03:07 PM   #3
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Is this a white metal frame with a very low temperature solder?

You can buy that braided steel stuff that Scalectrix used for their electrical track picks up (those two bits under the font of the car). If you put a little flux on it and heat the joint up, it draws off the solder like a kitchen towel. I'd be very wary with a white metal frame though. It melts at the same temperature as ordinary tin lead solder and you might end up with a blob of molten Eagle frame. That's why a very low temperature solder is used for white metal. Carr's do a range of specialist solders including white metal solder but I didn't mention them as they don't really apply to brass soldering. Out of interest, they even do one that melts at 90 C. You can make joke tea spoons that melt in the cup.
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Old 21-09-2005, 03:25 PM   #4
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No this is a brass (I think) backbone frame believe it or not, but put together in a very sloppy manner.

Don't know the thicknesses of the material, but it looks OK. I just don't have the workshop facilities to make a frame from scratch or I would have done it some time ago.

Thanks for the recommendation on the scalextrix parts though - it might well work...

I do have a flame torch, and some solder - got to get some flux.

I'll bring the frame along on Saturday so you can have a laugh...

The side cages are however white metal and very heavy...but the casting is not too bad and fairly easy to clean up.
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Old 21-09-2005, 03:31 PM   #5
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If it's brass, that makes things a lot easier. Maplins keep that steel braid but I've used strips of brass to do the same job. Basically anything that wicks away the excess solder will do. If all else fails, just make sure there's no sticky flux residue left and you should be able to clean up the joints with a file. Bring it this weekend and I'll have a look if you like.

EDIT: I'm calling that braid "steel" but in fact I think it's nickel plated copper.
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Old 07-11-2012, 03:31 PM   #6
troy0571
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Hi i im rebuilding my mattel eagles main bay landing gear and ran out of brass i was useing now the new brass isn't soldering do you know whats hapining ?,there little parts ive cut out of brass , the first one went ok couse i used up what i had of my old brass. you can find my work on this thread Space 1999 Eagle Transporter Forum > Main Mission > Launch Pad
Mattel Eagle: Restoration and Upgrade
i ended up haveing to use insta weld .do you think the insta weld shoud be good enough?these landing gears are just for looks and dont actualy work not like the mains which came out good.

Last edited by troy0571; 07-11-2012 at 03:36 PM.
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Old 07-11-2012, 08:37 PM   #7
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Quote:
Originally Posted by DX-SFX View Post
If it's brass, that makes things a lot easier. Maplins keep that steel braid but I've used strips of brass to do the same job. Basically anything that wicks away the excess solder will do. If all else fails, just make sure there's no sticky flux residue left and you should be able to clean up the joints with a file. Bring it this weekend and I'll have a look if you like.

EDIT: I'm calling that braid "steel" but in fact I think it's nickel plated copper.
What you're describing sounds like something called "solder wick" in the US. It can be found in US Radio Shack stores with all of the other soldering equipment and supplies. It's really great stuff for removing excess solder.
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