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Soldering, Where Am I Going Wrong?

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Dai Fledermaus19/12/2014 16:03:08
1030 forum posts
52 photos

As a callow youth, I seem to remember having no problems soldering fuel tanks together from galvanised tin plate for some of my control line models, but at the moment I can't seem to keep my soldering iron clean enough for more than a minute or two to solder some undercarriage legs together.

I've bought and tried various paste type flux, but the copper tip of my 70watt iron soon goes black, so I have to stop, let it cool and clean it up again to a bright copper finish only for the same thing to happen again. Time consuming and very frustrating.

The only flux I haven't tried is Bakers Fluid, only because I can't buy it locally. Could this be the answer?

Andy Green19/12/2014 16:17:58
2279 forum posts
67 photos
2 articles

You don't want a copper finish, the solder will eat copper, that what the tin coating is for. No need to let it cool, use a damp tea towel, and just wipe on that, with the iron at working temp.


TigerOC19/12/2014 16:37:10
309 forum posts
13 photos

Confirm what Andy said. You need to break the tip in so that the tip and area above has a nice shiny silver sheen and keep it like that using a damp cloth or damp natural sponge. If it gets dirty flood the tip with cored solder and bang it off and then wipe.


Edited By TigerOC on 19/12/2014 16:37:50

Braddock, VC19/12/2014 16:52:12
1633 forum posts
82 photos

U/C legs and soldering thereof can be one of life's greatest trials; sacrificial insulation is what you need.

Cyno together two bits of wood, hard balsa is good, with a rightangle between them. Face the inside with several folds of kitchen foil or cut up a beer/coke can or similar, just ensure that the shiny side is toward the outside.

Place over the wire to be joined ( I cyno mine to the leg, one less thing to worry about) and let your iron heat up whilst you were making this, needs a good 10 mins to stabilise. File the tip shiny beforehand then using multicore run some over and wipe off as suggested (damp paper towels is what I use).

Then solder - you shouldn't need to move your insulating thingy, just ensure that the uncovered back is uppermost so all the heat rises to the wire. Feed your solder in from the top.

Fixed it for me oh and I use the copper wire from 2.5 mm squ mains cable to bind the joint. The wire on my Wot4 took about 2 - 3 mins before it was hot enough to fuse the solder and I use a 100 Watt iron.

Plummet19/12/2014 17:01:58
1394 forum posts
41 photos

Just a thought. Are you using an old soldering iron and new solder?

The new elfin safety solder is lead free and needs a higher temperature, and is a pig to use. You can, however, still buy the old stuff at some places.


monty219/12/2014 17:23:06
102 forum posts

Perhaps you should look at the Galvanising, That is probably the issue, try using some sandpaper or emery cloth to remove the galvanising. that is always a pain for paint or other coverings.


Edited for language

Edited By Biggles' Elder Brother - Moderator on 19/12/2014 18:01:04

Dai Fledermaus19/12/2014 17:24:02
1030 forum posts
52 photos
Posted by Plummet on 19/12/2014 17:01:58:

Just a thought. Are you using an old soldering iron and new solder?

The new elfin safety solder is lead free and needs a higher temperature, and is a pig to use. You can, however, still buy the old stuff at some places.


That's interesting. The solder I'm using is solid wire and it is lead free, the flux is a water soluble type both from B&Q. The iron is perhaps 8 years old. I can tin the tip of the iron O.K. but it doesn't stay that way for long and brushing on some flux or dipping the iron in the flux doesn't seem to make much difference. I haven't tried the damp cloth method, but I will.

I seem to remember using a flux which was a liquid, perhaps it was acid based rather than a paste and dipping the tip of the iron in that cleaned off all the crud.

Vecchio Austriaco19/12/2014 17:30:24
1498 forum posts
707 photos

lead free solder - This may probably the issue Fledermaus! I stocked up with several different soldering wires 5 years ago. Cannot be bothered to throw away all my soldering equipment.


kc19/12/2014 17:56:33
6032 forum posts
168 photos sell old fashioned tin lead solder which melts at 183C to 188C ( lead free melts at 207C to 217C they say)

Biggles' Elder Brother - Moderator19/12/2014 18:10:31
15748 forum posts
1460 photos

Leaded solder is definitely easier. The claim you occasionally hear that it's very difficult to get, or even that it can't be bought now, is nonsense. It's not allowed for commercial operations but perfectly legal and available for hobby use - but you have to go to an appropriate supplier - not B&Q!

I worry about all this stuff about filing tips! I've never filed a solder tip yet, and never needed to and in fact I think that filing most modern tips would be very bad for them. I use a damp natural sponge pad that is set into my soldering iron stand combined with a very occasional dip into the flux and the iron remains tinned.

One thing that is slightly non-standard is that I use 9% phosphoric acid as a flux. This is an excellent flux, cleans wonderfully. The only downside is you do have to carefully rinse any joints under running water afterwards to make sure that all traces of the acid are removed. Nothing is for free!


G-YRUS19/12/2014 18:23:14
75 forum posts
1 photos

I solder nearly every day, admittedly copper tube but I use my work flux on piano wire etc and have no issues no matter what the so called experts say in the magazines. Use one of the self cleaning fluxes readily obtainable from usual outlets and wipe off with a damp cloth on completion. Concur on above and keep your iron tip clean with a damp cloth but tinned with solder don't sand it of.

The above assumes your not soldering electrical components as these are not good fluxes.

Temperature control is important and most faults are due to a low temperature so an adequate size iron to the size of job is a must, trying to heat something to slowly burns the flux as does to hot. Now I would say I am an expert and I use a flame on all my wire etc but do have various nozzles and 40 plus years of practice.

I also have a really good quality iron with various tips and temperature adjustment.

Lead free solder requires a slightly different technique as its melting point is higher and is more brittle when cold. Its just practice looking for the metal and flux colour as you heat it and feeding the solder at the right time. I guess the useable temperature range is smaller but I don't really need to think about it when working.

Lead based solder is still available and I cut down mine to size required.

Soldering came up in another thread and MAPP gas was mentioned. Reserve this for silver soldering as it is really for refrigeration work and burns much hotter than propane but can be useful outside in the winter.

Dai Fledermaus20/12/2014 10:12:48
1030 forum posts
52 photos

Thanks for your thoughts on this fellers

Kevin 21620/12/2014 10:48:49
204 forum posts

I also had difficulty getting the solder to stick. I now clean the wire with a dry scouring pad, pre-tinned copper wire (available from CPC) and silver solder (from Maplins), and a 100W iron. So far the results have been good.

FlyinBrian20/12/2014 13:09:44
522 forum posts
Posted by 216er on 20/12/2014 10:48:49:

I also had difficulty getting the solder to stick. I now clean the wire with a dry scouring pad, pre-tinned copper wire (available from CPC) and silver solder (from Maplins), and a 100W iron. So far the results have been good.

I don't think you mean "silver solder" as that requires much more heat than an iron can provide.

Plummet20/12/2014 13:27:55
1394 forum posts
41 photos
Posted by FlyinBrian on 20/12/2014 13:09:44:
I don't think you mean "silver solder" as that requires much more heat than an iron can provide.

Well... I think that there is a terminological problem here.

If my memory is not playing too many tricks I think that there is a form of low temperature silver solder, the purpose being to provide a very low resistance (electrical resistance - ohms and all that) joint.

The other sort of silver solder is more like a brazing rod, and you need a lot more heat - in that the metal glows - to use it.

Type 2 is, I believe, a lot stronger than type 1 which is only intended for electrical and not structural purposes.

Confusing isn't it.


Dai Fledermaus16/01/2015 13:53:01
1030 forum posts
52 photos

Problem solved!

It wasn't my iron. It wasn't the solder I was using. It wasn't my technique. I simply used a different flux to the paste types I was using previously, ie Baker's Soldering Fluid No3 and ..........................


Danny Fenton16/01/2015 14:43:09
9106 forum posts
3945 photos

I am not sure that is solidly soldered. I would expect the solder to have flowed over the piano wire, your picture seems to show solder as only flowing on the thinner binding wire...

This pic is from Andy Greens thread and shows what I would expect to see.

Just a thought and of course I might be misinterpreting your photograph



G-YRUS16/01/2015 15:03:32
75 forum posts
1 photos

I would second Danny it looks like the solder has not taken to the piano wire just the wrap.

Engine Doctor16/01/2015 15:11:47
2300 forum posts
27 photos

I agree with Danny Fenton , that joint is not properly soldered. one good knock and it will all come loose It looks from the pic that the piano wire needs proper cleaning and tinning (coating with a thin layer of solder)prior to assembly . Clean wire only with glass paper and not emery or wet and dry paper. They can often impregnate the surface with carbon that will reject solder . Once tinned bind joint with clean copper wire , apply some Bakers Fluid flux and solder all together . The solder should as said flow onto the wire as well as the copper. Solder will flow easily onto copper as it has an affinity to it . A Trick I was taught at school in metal work class for tinning steel or piano wire or any ferrous metal is to clean the metal thoroughly then dip it into a solution of Copper Sulphate . This leaves a very thin coat of copper particles on the steel that will attract the solder making soldering easier . The picture also looks like not enough heat is being use. What size iron are you using ? You will need a decent sized iron the higher wattage the better . Suggest a 100W . The old fashioned heat up up type that you heated on the cooker work well but again you need a decent sized tip to store enough heat for the job. If you have a small blow lamp then it could be soldered with that by heating just at the edge of the joint after preparing it and allowing the heat to travel through the joint allowing the solder to flow with it .

Dai Fledermaus16/01/2015 15:26:20
1030 forum posts
52 photos


Looks can be misleading. The two legs were soldered together first, the joint cleaned really well, then wrapped in copper wire and soldered again, the fact that you can't see that in the photo doesn't mean that it's a weak joint and "that a good knock and it will come loose"

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