# Resistance Soldering question



## PatriceL (Oct 5, 2019)

Hi. My name is Patrice Lemée and I am a metal sculptor.

I need help with resistance soldering and this seemed like a good place to ask. It’s hard to find people using this and I think you guys do. It’s not about trains so I hope it is still ok to ask. Let me know if it’s not.

I have purchased a soldering unit from American Beauty. Very happy with it so far but I am having a small problem. Well I hope it’s small.  I am trying to solder a small piece to a much larger piece as you can see in this picture. 










The thing is I need to put a lot of heat into the larger piece for the solder to properly flow to it. The result is a perfect solder joint but the carbon electrodes leave marks. Since I am doing this on a near finished sculpture and in hard to reach places I need to minimize this scarring of the surface. Not sure how to do that or if it’s even possible. These are carbon electrodes and they glow red hot from heat, more damage from the electrode e that glows more and also a little powdery residue on it afterwards.

Not sure if I explain myself well or if anyone here has an idea of how to do this better but I am taking a chance and would be very grateful for any help. Or of course if anyone knows of a better place to find info on this that would be great.

Here is my latest sculpture and the small feet are what I am working toward soldering.










Thanks for you help.


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## gunrunnerjohn (Nov 10, 2010)

Can't you put the electrodes on the piece under it to minimize the visibility of the marks?


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## wvgca (Jan 21, 2013)

it may be necessary to use a 'sacrificial' piece under the electrode, to reduce the scorch marks , or a larger electrode that will increase the area of contact, and reduce the number of amps per square inch


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## flyboy2610 (Jan 20, 2010)

I can't help with the resistance soldering question, but I want to say that's a nice piece of work!


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## PatriceL (Oct 5, 2019)

John, I can't do that but I may have to live with the marks and incorporate them in the design if I can't get rid of them completely.

WCGCA, that is an interesting idea but I have no idea how I would implement it since it usually is on a curved surface and a bit cramped. But I'll look into it some more for sure.

Flyboy, you are very kind, thanks.

And a big thanks for the help guys, I'll post more if I get better results.


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## gunrunnerjohn (Nov 10, 2010)

Remember, the one electrode can be connected anywhere on the piece, it's the current that does the heating.


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## PatriceL (Oct 5, 2019)

John I use a pliers stile handpiece, not a probe with a lead connected to the piece.


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## gunrunnerjohn (Nov 10, 2010)

It's quite possible that soldering on a finished piece simply isn't in the cards. I do wonder about the glowing electrodes, perhaps the excessive heat at the spot is the problem. Resistance soldering is supposed to heat the workpiece, not the tool. I've only used one resistance soldering rig, it was hand made. However, we had no red hot electrodes.

Have you considered low temperature solder for the critical pieces? Another option might be brazing or soldering with a torch, you don't get contact scoring with that method.


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## PatriceL (Oct 5, 2019)

I'll make it work John, even if like I said it means a little scoring that in the end I might be the only one that notices it. The drawback of being a tad perfectionist (ok maybe more than a tad  )

The red glowing is really just because I am dumping a lot of heat it doesn't happen until late in the process. Pulsing it might help too, got to try that some more.

I did not mention it but brazing would mean OA or Oxy-Propane and I can't have that because of insurance since my shop is attached to the house. That's why I am pursuing electricity based solutions. The solder I use is a low temp one for silver solder that is. About 435F if I remember right, not sure they make lower than that in silver which I like because it stays bright. (This one is named Stay-Brite after all )

Thanks again for your help.


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## gunrunnerjohn (Nov 10, 2010)

That's pretty good for silver solder. Dumb question. Why not use a large soldering gun like the Weller D650, it's a 300W model and will do significant soldering on large pieces. Resistance soldering may not be ideal for the work you're doing. You won't have any discoloration due to excessive temperatures at the contact point.


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## wvgca (Jan 21, 2013)

The electrodes shouldn't get hot to the point of glowing .... at least on mine they don't ??


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## PatriceL (Oct 5, 2019)

I do have one of those John and will give it a try. Now sure though that the 300W will be enough for that large a heat sink but it's worth a try, thanks.


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## PatriceL (Oct 5, 2019)

WVGCA, good to know, let me try a few lower settings to see. Thanks.


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## gunrunnerjohn (Nov 10, 2010)

I think you'll find that a 300W soldering gun will put out a lot of heat.


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## wvgca (Jan 21, 2013)

for a little more heat on the 300 watt iron, replace the tip with a piece of ordinary house wall wiring, in 14 or 12 gauge ... they make excellent tips, and the cost is very low .. solid copper wire ..


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## PatriceL (Oct 5, 2019)

WVGCA, I tried a lower setting and get some glowing almost instantly. I am troubleshooting that with the company I bought the machine from. Not sure what is happening.

John, I was wrong the Weller I have is the 140W model. I still tried it and definitely doesn't put out enough heat. I'll will try and make the resistance machine work before I buy that 300W to try. Gotta justify that 2500$ price tag.


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## gunrunnerjohn (Nov 10, 2010)

$2500??? Where did you come up with that price???

Weller D650 Industrial Soldering Gun, $56.99.

You could also consider the Wall Lenk LG400C 400W/150W Heavy Duty Watt Soldering Gun, $78.00.


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## PatriceL (Oct 5, 2019)

Oh no John I meant for my resistance soldering machine. It's from American Beauty. Got 2 handpieces with a few extra tips. Add shipping, taxes and duties.


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## gunrunnerjohn (Nov 10, 2010)

I can't help you with an existing purchase, but it's dirt cheap to explore the alternatives, especially based on spending $2500 on a solution that isn't working for you!


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## wvgca (Jan 21, 2013)

the Weller, if it's the same as the one i got, is 100 watt low, and 140 watt high ...
the household wiring thing works great .. it -may- be enough , easy to try it out ??


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## gunrunnerjohn (Nov 10, 2010)

I have the 100/140, it does well. However, for heavier pieces, I suspect the 300W model would be sufficient. If not, I also posted a 450W model. All of these are less than $100, so it's pretty cheap to have the tool. Even if it doesn't work for every situation, one of those will likely do most of the soldering you do. I've soldered a lot of brass, including some pretty hefty pieces, with the old Weller 100/140W gun.

None of these will leave burn marks on the material, the object of the exercise. Truthfully, resistance soldering isn't really for finished pieces, one presumes you're going to finish the piece after soldering as a rule.


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## PatriceL (Oct 5, 2019)

wvgca, I did try your trick with solid copper wire in my 140W and if did not have enough heat sadly. That's why I went with the induction machine, heat is delivered very quickly, anything slower and the heat is just sucked away by the large part. It's about maybe 1" round stock in this case solid stainless steel. Don't even know if the 300W would do it, maybe the 450? I'll still continue to give it a try with the induction. I know it's a very versatile machine and won't be wasted but maybe I am just asking too much of it. We'll see. Thanks again guys for your continuing help.

Oh and I forgot John, I am not looking for no finishing afterward at all, just trying to minimize it as much as possible because of how hard it is to do and do well.


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## gunrunnerjohn (Nov 10, 2010)

You're trying to solder stainless steel? Are you using the correct flux? I still say for less than $100 that I'd try the 450W iron. I didn't think the 140W was going to do it.


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## PatriceL (Oct 5, 2019)

Yes John, bronze to stainless steel in this case. I do have a solder that I know works great, it's just a matter of getting the steel to temp where I want it to.


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## gunrunnerjohn (Nov 10, 2010)

I'd be pretty surprised if 450 watts can't heat 1" round stock sufficient to solder.


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## PatriceL (Oct 5, 2019)

John the only thing I am worried about is that it says 400w but 150w continuous. So if it drops after the initial heat (like most do I think) i might not get that 400 for very long.


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## wvgca (Jan 21, 2013)

I didn't realize that you needed for one inch solid stainless steel rod ... no , 140 watt probably wouldn't be enough, even with the household wire trick ...
I have soldered quarter inch solid stainless wire with the Weller 140, and it did that well.. my sister needed one made up for a garden arbor in the shape of a web, sortof, lol .. maybe three feet by eight feet, donor material was gotten from an exhibition display made by a friend of hers, Alison Norlen of Saskatoon ... exhibition displays are normally set up for an exhibition and if not sold, are then taken down sometimes just for the parts within ..
She works mostly with stainless steel wire .. so I do have -some- knowledge of working with it ..very limited though .. she uses a small MIG welder for the heavier stuff ..


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## gunrunnerjohn (Nov 10, 2010)

PatriceL said:


> John the only thing I am worried about is that it says 400w but 150w continuous. So if it drops after the initial heat (like most do I think) i might not get that 400 for very long.


I believe the 400W cycles in and out to maintain the temperature. From a review on Best Soldering Stations.



> On Amazon, it has a very good rating. This tool had not any significant issues only what few customers complained is wattage problem, it can drop from 400 to 150, but I think it is because of improper using. Most of the customers say only good for it and you can check it out in Amazon reviews.
> 
> You should not look for another soldering gun. This one works perfectly and it is comfy.
> It is easy to use and you will not find a more practical gun.
> ...


I'll stop trying to convince you, it seems you've made up your mind.


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## PatriceL (Oct 5, 2019)

gunrunnerjohn said:


> I'll stop trying to convince you, it seems you've made up your mind.


Never my friend, just curious. Just bought the 260W one cause it was sold locally. Off to give it a try now, results later.


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## wvgca (Jan 21, 2013)

PatriceL said:


> Never my friend, just curious. Just bought the 260W one cause it was sold locally. Off to give it a try now, results later.



okay, you've had an hour .. 
how did the 260 watt do ??


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## Don F (Dec 5, 2015)

Is preheating the lager piece in an oven possible. This would allow for a lower temp needed to solder, and could possibly allow the use of the larger soldering gun that was suggested. Preheating is a common technique used for several metal joining processes. Also, the dis colorization from the soldering can be used as part of the project in certain circumstances. Years ago, there was a discussion on the OGR Forum about resistance soldering that was quite informative. there are several different types as well. Have you considered the new lead free solders? They can be just as effective as silver solder, but at a lower temp. I built a model of a steel bridge using steel components, and had very good success using lead solder. I did use a torch, but resistance soldering was recommended by several members of the OGR Forum, and a friend offered to lend me his. I had already finished the project at that point.


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## PatriceL (Oct 5, 2019)

wvgca: Nothing it did not work at all. Not any better than the 140W so little that it makes me think that 400W will not be enough. The machine I am using is 1800W and I need close to the top setting to generate enough heat. Of well it was worth a try. (Maybe it has to do with the tip, maybe I need to experiment there with different shapes to transfer the heat to the piece better.

Don, I would love to find that discussion, I'll see if I can. Preheating is not very practical as it will discolor other parts or other materials on a piece that I will also have to clean afterward. The resistance machine is starting to work better, and the marks I think I can diminish with time and practice and tweaking the settings. Or as you say make them part of the design. Softer solders would be nice but it will take time to find some since there seem to be a million of them. I would like something that stays bright even after years and if possible something that is as non toxic as I can find even if I do have a good fume extractor setup. The quest continues.

Thanks again for your help gentlemen.


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