# Soldering



## rebush (May 24, 2012)

Almost finished with my first engine a little Elmer's. The air intake is 1/8" brass tubing soldered into a brass bushing. I went to Youtube and all the videos were on wire, circuit board or copper roofing. I got it soldered but it took me about 2 hour to clean it up and make it look presentable. Are there any book that give good descriptions with pictures for the type of soldering needed on model engine building. I've got a pencil style iron and a regular propane torch. I'm thinking I'd have better results with a small butane torch for more pin point heat. Any help would be greatly appreciated. Roger


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## picclock (May 25, 2012)

Hi Rebush

Three things spring to mind. 

If its a compressed air engine the fixing could be done with clear epoxy which would look smart with no pain and no cleaning. Also has the added benefit of disassembly by heating the parts to 250C which will cause the epoxy to fail.

Are you silver soldering or soft soldering ? The heat required for soft solder is <300C whereas silver solder (brazing) is 700C plus. Either way a small propane torch will give a higher heat output than a butane one. 

Silver Soldering (brazing) is mostly used for joints that are subject to high mechanical stresses or elevated temperatures, as in boilers. The joint is allegedly as strong as the materials joined. For cleanup, jobs are immersed in a 'pickle' (typically a citric acid solution) for an hour or so, which removes flux and oxides. 

Soft soldering is not normally used for any work where mechanical stresses occur, as its main constituents are tin and or lead. Most uses are as an electrical conductor for circuit components or in plumbing joints, although these are now being superseded by oring sealed push fittings. The flux is often contained within the solder, and whilst this is OK for electronic work it will not be sufficient for mechanical joints. For Plumbing use flux must be applied separately. It can be easily obtained from plumbing suppliers or diy shops. 

Not sure if this gives you the info you need.

Best Regards

picclock


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## Sshire (May 25, 2012)

My first silver (hard) soldering attempts were quite a mess. Too much solder, too much flux, solder way beyond where I needed it.
I have since moved from wire solder to silver solder paste. I believe this is silver solder particles mixed with flux. It comes in a syringe with a fine "needle" with a flat end. This gives you the ability to put a small amount of solder precisely where you need it and not where you don't. Also, graphite prevents solder from sticking. So I usually draw a circle around the area with a soft pencil. This acts like a barrier to contain the solder.
After melting the solder, I mix some citric acid (I get it at a local spice store)and water in a small dish and drop in the parts for an hour or so. Minimal cleanup and very neat joints.

I ordered my paste from these folks
http://sra-solder.com/section.php/2/1

The small syringe of paste that I have looks as if it should last for a long time because so little is used for a joint.
Hope this helps
Best
Stan


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## krv3000 (May 25, 2012)

hi well their is books out their but its like every thing its practise with both types of soldering it all must be spotless with soft soldering yous plumes flux for hard fixings but not for electrical work yous proper flux for that and the other thing is heat in both cases you can have to much and too Little you can get soldring ions witch are temp-recher controlled by wot sis tip you put in the ion but the rool of thum the biger it is the more heet you will need


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## Blogwitch (May 25, 2012)

You will usually find that ready mixed silver solder paste is a 'lifed' product. Usually rather short, so only buy the smallest quantity available for the job, otherwise you will end up throwing most of it away after it goes out of date, and it makes a real mess of your job if you do use out of date stuff, the flux tends to fail rather dramatically.

I know this because I used to condemn kilos of the stuff, when I used to find the operators never used correct product date rotation. The silver solder paste we used to use came from Johnson Matthey, and it had a storage life (if kept in the usual cool dark place) of, as far as I can remember, one year.

So if you buy it off the shelf, look to see how much life it has left, or only buy it direct from the manufacturer.


John


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## Henry (May 25, 2012)

For almost any kind of solder clean as much as possible, use the minimal amount of solder (normally the newbies think that more mean stronger) most of the solder use the capillarity effect( the pieces need to fit but not too much) and the solder move to the flame or the hottest area in the work .
I am lucky and in my work I use a laser for solder you can solder more than 5 points in a millimeter with the pieces in you hand.


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## Ed T (May 25, 2012)

In order to make neat joints with either hard or soft solder it is important to control the amount of solder being used. As noted above, it doesn't take much to make a sound joint if the parts fit reasonably well but not so tight that the solder can't wick down between them. I have had success by cutting small pieces of solder around the same length as the diameter of the solder (called pallions in the jewelry soldering business) which I place on the joint after the flux is applied. The size of the joint dictates how many to use and I don't know of a formula that tells how much is enough, experience will teach you that. If it's not enough you just add another little piece 'til it looks right. This avoids getting way too much solder in/on the joint which may work OK, but is a pain to clean up. For soft solder, I like Harris Sta-Brite and its associated flux. Their website has a lot of info on hard solder as well so I'm not going into the various kinds here. With any soldering job, there are only a few key points:
  1) The parts must be clean
  2) The parts should fit together well. Most solder is a poor filler.
  3) Use the right flux and enough of it.
  4) Get it hot enough for the solder to flow freely, but not so hot that you are burning off all the flux. 
I have found that a propane torch is adequate for hard soldering small parts, but only just. Soldering on a fire brick helps a lot if your torch is on the cool side. As with most things practice helps a lot. If I have a tricky joint to make I often mock up the tricky part and run a test. This is to avoid ruining the real parts with a botched solder job.


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## rebush (May 25, 2012)

Sshire: Which product did you order. I would think you'd want a free flowing with strong flux that can be heated with a torch. I have a propane torch with a nozzle to heat parts on the motorcycles for interference fits. Should I be looking for a more pinpoint tip to better locate the heat?

Bogs: As long as I keep track of the expiration dates on the paste do you think I'd have better luck. What I'm currently using is a paste flux and the solder spool said it was for metal working. 

Thanks to everyone who responded I did make sure all the parts were clean. Now it's just down to practice. Everyones getting some mismatched strange shaped soldered earrings for Christmas this year. Roger


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## lemelman (May 26, 2012)

Bogstandard  said:
			
		

> You will usually find that ready mixed silver solder paste is a 'lifed' product. Usually rather short, so only buy the smallest quantity available for the job, otherwise you will end up throwing most of it away after it goes out of date, and it makes a real mess of your job if you do use out of date stuff, the flux tends to fail rather dramatically.
> 
> I know this because I used to condemn kilos of the stuff, when I used to find the operators never used correct product date rotation. The silver solder paste we used to use came from Johnson Matthey, and it had a storage life (if kept in the usual cool dark place) of, as far as I can remember, one year.
> 
> ...


I'm a goldsmith with about 50 years of experience and use hallmarking quality gold and silver solder for almost everything I make. The silver solder is basically the same as engineering quality silver solder, except that it contains more silver; gold solder is the same, except it uses gold instead of silver.

For some applications I use solder paste, and after a while it goes so hard in the syringe that it can no longer be extruded. Gold solder, in particular, is far too valuable to throw away so I simply refresh it by scraping it out of the syringe and mixing it with a few drops of pure turpentine until it has the correct consistency again. Back in the syringe it works as before - and has a nice smell (if you like turpentine). Turps substitute doesn't work; it has to be pure turpentine.
It lasts for years like this.


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## Sshire (May 26, 2012)

Bogs
Thanks for the shelf life tip. I'm wondering if the turpentine tip wil "resurrect" the characteristics of the material or just allow it to be used, still with a shelf life of a year.

I got the cadmium-free, semi-restrictive paste from SRA.

A good how-to is here
http://modelsteam.myfreeforum.org/archive/using-solder-paste__o_t__t_35526.html

Best
Stan


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## Blogwitch (May 26, 2012)

Roger,

By the sounds of it, you are using soft solder, not a hard silver solder.

This is where us Brits get very confused over your terminology.

We call what you call silver solder, soft solder, used for plumbing and joints that don't require much strength. Soft soldering is usually frowned upon by the model engineering community, purely because of it's distinct lack of strength, we would only really use that if we had to caulk something, say a brass or copper fuel tank, or fixing multiple parts together so that they can be machined as one unit, then split apart again, say for making split bearings.

Our silver solder is, I think, what you would call silver braze. This is used where very strong joints are required on copper based alloys and steels.

In the US, I think everyone and his dog must make solders and fluxes, and so confusion reigns when you start to talk with brand names, as each seems to have it's own 'world beating' properties. 

We normally only refer to it as hard (silver solder) or soft (plumbers solder) soldering, so the same confusion isn't present. 
All we need to do for hard soldering is choose the melt range and flux, which over here, the most popular flux seems to be Tenacity 5, which seems to cope with everything from copper to stainless steel. There are lots of other brands, but they all basically work the same way. For soft soldering, almost anything that will do the job without being expensive, I tend to use non leaded solder and it's relevant flux.


John


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## lemelman (May 28, 2012)

That's a valid point Roger. 
In my opinion there are two basic methods of joining metals with molten (filler) metal: soldering and welding. 
Welding uses a filler with the same melting point as the metal to be joined; its usually the same metal. Soldering uses a filler with a lower melting than the metal to be joined.
Soldering can be divided into 2 main groups: soft and hard; mainly characterised by the melting point. Soft solder used to be mainly lead, had a melting point lower than about 250C, and could be applied with a soldering iron. Nowadays, lead is replaced by other metals. 
Hard solder has a melting point above 250C - usually higher than 500C, and is impossible to apply with a soldering iron. 
The original hard solder was brass, and the process was known as _brazing_; it was typically used for joining ferrous metals. The melting point of brass is very high compared to the melting points of non-ferrous metals, which makes brazing them rather difficult, so a new filler was developed based on _silver_; this was called _silver solder_.
Nowadays in UK many people, myself included, reserve the term _brazing_ for when using brass as the filler, and think that the American term _silver brazing_ is a contradiction in terms. 

Gary


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## lemelman (May 28, 2012)

Sshire  said:
			
		

> Thanks for the shelf life tip. I'm wondering if the turpentine tip wil "resurrect" the characteristics of the material or just allow it to be used, still with a shelf life of a year.


In my experience, the turpentine doesn't affect the essential characteristics at all; the solder melts as before, and the built-in flux still does its job. The only differences I've noticed are that the paste smells of turpentine (strange that), and briefly catches fire when the flame is applied. I don't use the paste form very often, and I'm still using some resurrected stuff that's at least 5 years old. I'm even using stuff that's been resurrected more than once!

Gary


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