Author Topic: Soft Soldering Piano Wire  (Read 2072 times)

Offline Allen Smithee

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Soft Soldering Piano Wire
« on: August 30, 2022, 11:46:31 AM »
40 years ago I started building a 1/4 scale Fournier RF4D as a background project which (for lots of odd reasons) only finally got finished and flown a couple of days ago. It has a retractable mainwheel which is fabricated from bent piano wire pieces soldered together:




<a href="https://www.youtube.com/watch?v=58xkH9zqlzM" target="_blank">http://www.youtube.com/watch?v=58xkH9zqlzM</a>

It would have been fine but on the 4th flight I forgot to release the spoilers before flaring and the resulting heavy landing snapped the 16swg piano-wire downlock latch:



When I made the original (in 1982) I made jigs to bend the 10swg wire struts so I made a spare set of wire parts which I still have, so I dug these out to make a replacement leg assembly. Soft soldering is preferred because it doesn't de-temper the piano wire like silver soldering would (it's pretty-well impossible to recover the temper with heat treatment because piano wire is "patented" rather than just hardened & tempered). In 1982 I did this using a 400w electric soldering iron, binding with fuse-wire and then soldering using an active flux (bakers fluid). When I came to try this on Sunday I found I could no longer buy decent acid fluxes in any shops around here, and my 400w iron no longer works. So my only option was to use a flame torch gently "wafting" to ensure the temperature stayed below 300degC and applying solder. But no matter how much I carefully cleaned the wire back to bright steel I could not get it to tin before the torch oxidised the surface again. The results were pretty ugly even by my standards:




I have no confidence in the strength of this, so I'm probably going to de-solder it all and start again. But what I really need is some decent acid flux for steel - can anyone recommend anything that I can buy in small quantities in the UK? Can anyone recommend a better way of going about it?

TIA,

AS
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Offline Jasonb

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Re: Soft Soldering Piano Wire
« Reply #1 on: August 30, 2022, 11:54:12 AM »
Cup do one though the postage is high. Give them a call and tell them what you ar edoing and they will confirm if it's OK

https://www.cupalloys.co.uk/store/CuPsol-Flux-125ml-p276411653

You can also buy Bakers fluid easily enough but again postage is high due to it being acid

https://www.cooksongold.com/Jewellery-Tools/Bakers-Soldering-Fluid-250ml-Un1840-prcode-998-127?gclid=CjwKCAjw6raYBhB7EiwABge5KtCHSFlDRbgz7ANfizTOwqeD7REkIVSCipGm4VOqTikVxVSn0s9CxRoCn2AQAvD_BwE&gclsrc=aw.ds#description
« Last Edit: August 30, 2022, 11:58:02 AM by Jasonb »

Offline Lew Hartswick

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Re: Soft Soldering Piano Wire
« Reply #2 on: August 30, 2022, 03:00:20 PM »
Something you could try!  Acetic acid ( an organic one,  white vinegar) or Phosphoric acid common in some of those "de-rusting" things on the market.
I remember the blue flux we used on PC boards back in the 50 or 60s was some sort of an Organic acid that neturalized when the soldering was done.
   ...lew...

Offline bent

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Re: Soft Soldering Piano Wire
« Reply #3 on: August 30, 2022, 04:56:42 PM »
I'm surprised local hardware shops don't stock zinc chloride paste flux?

Offline Allen Smithee

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Re: Soft Soldering Piano Wire
« Reply #4 on: August 30, 2022, 05:34:08 PM »
What is this "local hardware shop" of which you speak? We only have DIY stores, and they only stock it if it is made of MDF and skinned in faux wood-effect plastic...

AS
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Offline Zephyrin

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Re: Soft Soldering Piano Wire
« Reply #5 on: August 31, 2022, 08:56:08 AM »
you can easily prepare zinc chloride flux...
simply by adding small pieces of zinc into hydrochloric acid  (the acid used to clean cement stains on tiles is suitable) up to saturation, i.e. until it no longer dissolves.
This solution clearly "wet" the piano wire, and the tin solder is perfect. rince and neutralise (sodium carbonate) after to avoid rapid rusting of the naked steel parts.





Offline Alyn Foundry

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Re: Soft Soldering Piano Wire
« Reply #6 on: August 31, 2022, 02:39:16 PM »
Bakers No 3 soldering fluid is readily available from my local welding supplies outlet.

Another avenue is your local Plumbing supply outlet. They should carry a range of flux pastes, there are some that say no initial cleaning is required.

And to follow up on Zephyrin’s previous post. I recently got some very strong Hydrochloric acid from eBay for a proposed electroplating exercise. Pure Zinc is also sold on eBay. Just dissolve the Zinc until no more will be taken, you now have the
“ killed spirit “ as it was known back in the day.

 :cheers:  Graham.

Offline Allen Smithee

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Re: Soft Soldering Piano Wire
« Reply #7 on: August 31, 2022, 04:12:39 PM »
Thanks for the hints, chaps. I've ordered a replacement 200W soldering iron and some Bakers Fluid rather than bodge it through impatience. I'll dismantle it tonight so that I can de-solder and clean it all ready for when the stuff arrives. I've got a tub of sodium bicarbonate to make a wash solution with so it doesn't start rusting afterwards.

Thanks again,

AS
Quidquid latine dictum sit altum sonatur

Offline derekwarner

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Re: Soft Soldering Piano Wire
« Reply #8 on: September 01, 2022, 12:20:05 AM »
Alan.....

100% agree on the Bakers soldering flux, however I don't think any 200W electric soldering iron will heat your components sufficiently to make a good soldered joint

These gas torches  :Mad:  are not really expensive & would be a good addition in the kitchen when not in use in the model making den  :naughty:

Derek
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www.ils.org.au

Offline Allen Smithee

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Re: Soft Soldering Piano Wire
« Reply #9 on: September 01, 2022, 07:59:52 AM »
I have gas torches, and that's what I used the second time. But I'd rather not use them for this because it's very difficult to avoid tarnishing the steel before it's up to temperature (preventing the solder from wetting to the steel) and it is also difficult to avoid destroying the temper in the wire by overheating it. Once overheated it is impossible to recover the temper in piano wire so you end up with an undercarriage that either bends because it's too soft or snaps off due to being too brittle (lacks toughness). The "patenting" process used to manufacture piano wire makes it extremely tough as well as springy, and that's an essential charateristic for this application.

AS
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Offline Alyn Foundry

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Re: Soft Soldering Piano Wire
« Reply #10 on: September 01, 2022, 11:07:38 AM »
Alan.

You surely must have an old “ Copper “ lying about your workshop ? I have several ranging from tiny to half a pound in weight? By that I’m of course referring to pre electric soldering irons. These were used by both Copper and Tin smith’s. I remember being taught how to use one at Sid’s radiator repair shop in Blackpool back in the 60’s. Each bench had a gas fired muffle, there were always several “ Irons in the fire “

A good hot Copper will carry enough heat for the job that you want to do. Thus avoiding the oxidisation problem.

 :cheers:  Graham.

Offline Allen Smithee

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Re: Soft Soldering Piano Wire
« Reply #11 on: September 01, 2022, 04:29:07 PM »
Nope, don't have anything like that. But I do now have one of these:





I feel like doing a Crocodile Dundee - "Nah - that's not a soldering iron. THIS is a soldering iron..."

 ;D

AS
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Offline Admiral_dk

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Re: Soft Soldering Piano Wire
« Reply #12 on: September 01, 2022, 04:51:57 PM »
OK - That IS a VERY Big Iron  :o

I only hope that it is a good Tip too .... as that is usually the first thing that goes with a Poorly made one ...

Even the Pro Soldering Irons has the Tip being the part that needs replacing from time to time - but there is a huge difference in the 'Between Time'  ;)

I hope this solves your problems so you can get it Airborne ASAP  :cheers:

Per

Offline Allen Smithee

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Re: Soft Soldering Piano Wire
« Reply #13 on: September 01, 2022, 05:25:30 PM »
OK - That IS a VERY Big Iron  :o

I always used to think size didn't matter. But then all my new wallpaper peeled off...

[the Humphry Littleton Memorial joke]

This iron will be used for things that I probably only need to do once every 4-5 years, so I'm not that fussed if the tip doesn't last.

AS
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Offline Allen Smithee

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Re: Soft Soldering Piano Wire
« Reply #14 on: September 01, 2022, 07:31:26 PM »
To round this off - cleaned back the parts, a dab of bakers fluid and that iron tinned the 10swg piano wire like it was stranded copper flex. Assembled the parts in a clamp, applied the tinned iron from the underside and the solder from above to tack it together, then wrapped in 1mm copper wire and filled the joint. Washed in bicarb solution to stop it corroding and the whole thing is now back in the aeroplane ready for Saturday.

Bottom line? No substitute for a big iron!

AS
Quidquid latine dictum sit altum sonatur

 

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