Resistance Soldering

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David B
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Re: Resistance Soldering

Postby David B » Fri Jun 07, 2019 2:19 pm

It's been a while since I posted about the RSU though the unit has not been idle in the meantime. I was talking to someone at Railex about the technique and they were very sceptical about it's use with white metal. I have just been putting the axle boxes and springs on to Jeremy's fish belly bogie (see his thread here) and thought I would post how it is possible (and neater) to use the RSU for this purpose.

First, I tinned the spring ends (which, note well, are handed) and the axleboxes with 100o solder. I know some people use 145o but we are working close to the corner which has also been soldered with 145o. Cleaning the surface first is necessary for better bonding.
Bogie RSU_2071.jpg


The bogie was similarly cleaned where the soldering was to be done. I used a new scalpel blade and you can see the powdery surface which has been removed.
Bogie-RSU_2073.jpg


The voltage was reduced for the soldering to 1.5v (from my usual 2 volts). This makes the process a bit slower and safer. I have marked where I put the probe - away from the end to reduce the possibility of unsoldering the corner. Make sure you do not touch the white metal with the probe. I held the end of the spring with ceramic tweezers and as the heat spread through the nickel silver to melt the 100o solder, a flash of silver (molten solder) is the signal to take your foot off the switch - the heat has travelled far enough and the corner remains solid. When attaching the axle box, I put the probe to the side of the 'W' iron. Again, as soon as a flash of silver was seen, foot off. The second side of the axlebox is quicker because the metal is already warm.
Bogie-RSU_2074.jpg


Finally, job done. and no cleaning up to be done providing you have not overdone the tinning, where you need very little solder. The missing corner of the right hand axle box is a dodgy casting, not my melting it with the RSU.
Bogie-RSU_2075.jpg


This might take a little longer than using a conventional iron, but the result is neater. I have presumed everyone knows about flux which is why it only now gets a mention.

A further point is that it is not necessary to solder the whole length of the spring - soldering the ends is quite sufficient. This principle applies to many other pieces yet I often see people smothering everything in solder. Solder is there to attach something and quite often, that something only needs a couple of points of attachment. Leaving the rest makes a neater job and less work cleaning up.

John Palmer
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Re: Resistance Soldering

Postby John Palmer » Fri Jun 07, 2019 3:09 pm

Of particular interest because I am approaching the point where I have to attach the combined axlebox and spring castings to four very elderly etched SR bogies.

This is a very neat piece of work, David, but the prospect of tinning those castings is one that fills me with dread - how did you go about that part of the job? Presumably not with the RSU?

Am I right in thinking that your axleboxes have ended up a bit low? There seems to be a quite substantial gap between the top of the box and the bottom of the spring buckle.

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David B
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Re: Resistance Soldering

Postby David B » Fri Jun 07, 2019 3:25 pm

You may well be right about the height of the axle boxes. Is the spring usually in contact with the box? I have never thought about this. If so, then it is a simple job to adjust them with the RSU - heat sufficiently to melt the solder and slide the axlebox up a tad (or 'substantial' amount). The springs are right. I mentioned that they are handed. The end hanger has a 'shelf' on the bottom which butts against the underside of the frame.

Tinning is done with a conventional iron. I use my trusty Antex temperature controlled iron and conical bit set on no more than 200oC. Very little solder is needed and I have never (never say 'never'??) yet melted a casting set at that temperature.

With a combined spring and axlebox, try soldering just the axlebox. I think you may find this sufficient.

John Palmer
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Re: Resistance Soldering

Postby John Palmer » Fri Jun 07, 2019 3:40 pm

David B wrote:With a combined spring and axlebox, try soldering just the axlebox. I think you may find this sufficient.

That was rather the way my thoughts were going. I assume that tinning of the white metal component is essential in order to get a satisfactory joint. Fortunately I have a temp. controlled Hakko iron in my armoury, so I may give this a try.

Yes, the central spring buckle needs to be be in contact with the top of the axlebox, as this is the way in which the weight of the vehicle is ultimately transmitted to the wheelsets. Fig. 136A in Russell's Pictorial Record of GW Coaches Part II illustrates this quite well on a fishbelly bogie.

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David B
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Re: Resistance Soldering

Postby David B » Fri Jun 07, 2019 3:49 pm

Thank you, John. The axleboxes are about to slide.

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David B
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Re: Resistance Soldering

Postby David B » Fri Jun 07, 2019 4:11 pm

Corrected. The boxes have gone as far as they will go because of the pinpoint bearing referred to in another thread.
Bogie-RSU_2077.jpg

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PeteT
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Re: Resistance Soldering

Postby PeteT » Fri Jun 07, 2019 5:48 pm

David,

Thanks for sharing! Very timely too, as I have a batch of 3 16T minerals (with Rumney underpinnings) which have just reached the axlebox stage, so I'll give this a go.

Likewise, there are things close at hand to avoid as after assembling the brake lever guards I have fitted them with 145 (I guess I could have tried 188 to give a bit more headroom). I'll try the technique on the two corners without these first!

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David B
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Re: Resistance Soldering

Postby David B » Fri Jun 07, 2019 6:12 pm

If you have not used the RSU with white metal, begin on a low(est) voltage setting. Nothing might happen, in which case go up a notch until you get the result you want. Do not plough in on a medium or high setting or your modelling could end up with tears and a blob of molten white metal.

Do not let the probe touch the white metal - it will melt it.

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PeteT
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Re: Resistance Soldering

Postby PeteT » Sat Jun 08, 2019 9:06 am

Thanks- I got the probe touching bit from your in depth description (and photos tell 1000 words) - but yes I take your point on starting at the lowest voltage and working up.

Two questions spring (no pun intended) to mind - firstly, in my application is this the best approach? What I have done before is flood with 100 degree solder from the blue circled area in the below photo, which gets a good amount of coverage (and as you say, this isnt a structural part so doesnt need a full seam all the way around the edge, which I have done and spent time cleaning up before!). My only nervousness is with making sure it sits down exactly where required once the solder melts - though I appreciate this would only really be an issue if too much pre tinning was applied.

20190608_093541.jpg
20190608_093541.jpg (121.8 KiB) Viewed 2025 times


Secondly, and apologies in advance (we sometimes go too far down the scientific vagaries here, rather than accepting that something works and going with it!) - but by my understanding of the general concept of RSUs is that you contact each side of the job, and that joint becomes the highest resistance and so locally heats the desired area. In this application, is it working on the basis that the NS/brass is more resistive than the cabling from the RSU, so even though not a spot of high resistance will be the area of resistance and so heat up? but would the two contact points between the probes/clips and the NS/brass not be higher anyway, and so just heat those two points more than the surrounding sheet? So effectively the heat will be created at the point the tip of the carbon rod touches, but the metal sheet then conducts that heat way more efficiently/quickly than the carbon rod?

Almost time to head to Warminster - see some of you there!

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David B
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Re: Resistance Soldering

Postby David B » Sat Jun 08, 2019 5:00 pm

I was at Warminster as well - sorry we did not meet. I did enjoy the show which was a really good get together with some delightful layouts.

Answering your questions.

First: I agree that putting the 100o solder with a conventional iron where you have indicated does work well. I have often done this myself. I keep saying this, that the RSU is not a replacement for a conventional iron, the latter sometimes doing a better job. In the end, it is what works best for you. On the bogie above, getting in behind was not an option and there was no opening anyway to use a conventional iron.

Second: Yes, you are right. This is the idea behind 'true' resistance soldering. However, the tip of the probe is also a point of high resistance so it can be difficult to know which, the tip or the solder, is generating the heat when the two are in proximity (most probably both). The ability of the probe tip to generate heat means that it can be used just to heat metal and in turn melt solder, as I did above to fix the white metal castings. This may not be the 'pure' way to use resistance soldering, but it works. In the end, it is about getting heat in to a joint to melt the solder and cement together two pieces of metal. Does it really matter how this is achieved except by a method that gives us the best (and sometimes easiest) results?

The RSU has advantages over a conventional iron in some situations and sometimes it is the reverse. Resistance soldering is a very useful tool which enables us to make better models, but it is not a magic bullet.

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Paul Townsend
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Re: Resistance Soldering

Postby Paul Townsend » Sat Jun 08, 2019 5:41 pm

David B wrote:I was at Warminster as well - sorry we did not meet.


Oh yes you did !
Too much excellent cake has rotted your memory ;)

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PeteT
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Re: Resistance Soldering

Postby PeteT » Sun Jun 09, 2019 1:53 pm

Paul Townsend wrote:
David B wrote:I was at Warminster as well - sorry we did not meet.


Oh yes you did !
Too much excellent cake has rotted your memory ;)


Indeed, & unlike Gordon I knew better than to let my cake out of my sight!

I've just done 1 wagon with a conventional iron, and will try the 2nd with the RSU. I agree it is horses for courses, both in different tools for different jobs but also when those jobs are carried out by different people. I'll experiment & see what works for me.

As you say David, even if in this instance I stick to the normal iron approach there will be times when other factors rule this put, such as on your bogie.

Michael Waldron
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Re: Resistance Soldering

Postby Michael Waldron » Mon Jun 10, 2019 7:52 am

I hope this will be forgiven as a bit of diversion, but are any of you users the proud possessor of a heart pacemaker?

I have rebuilt my late father’s car battery charger into an RSU, quite successfully, but have since then had to have a pacemaker fitted, and have been warned by the technicians to avoid magnetic fields.
When I asked someone at the hospital a while back about the warning about using microwave ovens, he said, “Only dangerous if you’re going to get into it!”.......! Haven’t managed that / needed cooking / been that cold as yet!

Seriously, though, does anyone have a definitive answer, or do I just need to erect a lead shield round it?

Mike
Last edited by Michael Waldron on Tue Jun 11, 2019 6:10 am, edited 1 time in total.

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David B
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Re: Resistance Soldering

Postby David B » Mon Jun 10, 2019 8:50 am

I do not have a definitive answer, Michael, though I know one should not leave credit cards or watches near the unit. I have not heard of any other concerns. My RSU is a couple of feet away from me so I would have thought that sufficient. My cards still work!

Then there are the magnets one uses on the work plate (if you have one).

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Noel
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Re: Resistance Soldering

Postby Noel » Mon Jun 10, 2019 11:11 am

Michael Waldron wrote:Seriously, though, does anyone have a definitive answer, or do I just need to erect a lead shield round it?


I would think that the only sensible answer to this is to obtain a magnetometer to measure the field strength your RSU generates, and ask the technicians what value the manufacturers of the pacemaker advise would produce a risk of malfunction if exceeded [which is likely to be on the cautious side]. Given the number of variables involved, anything else would be guesswork.
Regards
Noel

Michael Waldron
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Re: Resistance Soldering

Postby Michael Waldron » Sun Jun 16, 2019 7:13 am

They’re seriously expensive, even on eBay!

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Jol Wilkinson
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Re: Resistance Soldering

Postby Jol Wilkinson » Sun Jun 16, 2019 7:54 am

Michael,

the RSU's on Ebay at present are all from the USA and mostly of the expensive American Beauty brand.

For those who prefer to do their own thing and save money, there are various websites and forums describing how to make RSUs from car battery chargers, microwave ovens, etc.

Otherwise there are two UK manufacturers of proven, ready to use, units,

Jol

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Paul Townsend
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Re: Resistance Soldering

Postby Paul Townsend » Sun Jun 16, 2019 8:27 am

Jol Wilkinson wrote:Michael,

the RSU's on Ebay at present are all from the USA and mostly of the expensive American Beauty brand.

For those who prefer to do their own thing and save money, there are various websites and forums describing how to make RSUs from car battery chargers, microwave ovens, etc.

Otherwise there are two UK manufacturers of proven, ready to use, units,

Jol

The AB range is large and expensive because it is aimed at the industrial market and designed for longevity when used continuously 24/7.
INMHO there is one item in the range of relevance to us...Tweezer probes, still expensive but hard to make

Michael Waldron
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Re: Resistance Soldering

Postby Michael Waldron » Sun Jun 16, 2019 10:40 am

Sorry Gents - misunderstanding - I meant Magnetometers to check for magnetic field re pacemaker diversion!!
Apologies, no hijack intended.
Please proceed - starter signal raised!

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LesGros
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Re: Resistance Soldering

Postby LesGros » Sun Jun 16, 2019 10:43 am

Paul Townsend wrote:
... INMHO there is one item in the range of relevance to us...Tweezer probes, still expensive but hard to make

I have one of these, it is perfect for controlling small and delicate components. It does not replace the other soldering tools, but certainly makes fiddly jobs easier to do.
LesG

The man who never made a mistake
never made anything useful

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David B
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Re: Resistance Soldering

Postby David B » Thu Jul 11, 2019 9:32 am

Fixing the window frames in to the end of the steam railmotor. I have tinned most of the way round these and all along the side nearest the fold (yet to be made) , as Jeremy has done on his build.

Because the frames are thin and delicate, I reduced the voltage to 1.5v which slowed the process a little. All I have done to finish is pass some fine Micro Mesh over the top, otherwise there has been no cleaning up to do.

Bolections_c3594crw.jpg

Bolections_c3595crw.jpg

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David B
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Re: Resistance Soldering

Postby David B » Mon Jul 22, 2019 9:15 am

I have had sitting in my 'maturing' box, a packet of two etches and four white metal posts which make up GWR yard gates. This is an old kit which came from Pendon Museum. When I bought them way back in the 1970s, I was rather taken with them but on getting home wondered how on earth I would make them without smothering them in solder.

Technology in the form of resistance soldering provided the answer, albeit more than 40 years later! I tinned just one side of the two outer layers (whilst still on the fret), placed all the layers together, lined them up with heat resistant tweezers and worked outwards from the centre of the top and bottom, fixing all three layers in one go.

Gates_3604crw.jpg

Gates_3607crw.jpg

Gates_3608crw.jpg


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