Soldering question

[Tim Kearsley]

I want to make a custom rudder horn for the project I'm currently working on (a Brian Taylor Cessna 120).  This will entail attaching a brass sheet horn to piano wire.  While I've done a large amount of electrical soldering in my time, I'm not experienced in heavier duty soldering.  I'm presuming it would be best to silver solder in this case?  Is silver soldering in essence similar to soft soldering but at a much higher temperature?  I've just ordered a "starter kit" from CupAlloys which includes flux and solder rods.  I have a butane blowtorch.  Any advice from the experienced builder gratefully received!

[Don Fry]

I would have used ordinary 70/30 Pb/Sn, and an acid flux. Bakers fluid. That said resin flux, and multi ore would do just fine.Not a high stress component, but you still need a 100 watt iron, or a soldering station. 
What often gets overlooked is it’s mechanically good if the brass is formed so the wire sits in a corner/channel so it’s supported better to reduce stress on the solder.

Silver soldering is higher temperature soldering. Practice, practice. Because that torch will melt brass, let alone ruin everything with oxidation. Practice off the final workpiece until you work out how to get the right temperature.

[David Holland 2]

Hi, Tim. Silver soldering really is not a black art, it is just as easy as soft soldering albeit with higher temperatures involved. The trick is to use a big enough heat source and heat until the flux is completely clear and very liquid (pretty much “red” heat). It is often easier to put a small ring of solder around the workpiece which will then “flash” into the joint when the required temperature is reached. Thin brazing rod is easier to use on small items and a propane torch is more than adequate, though standing the workpiece on refractory blocks helps a lot. I think those lightweight building blocks work well but I use a purpose made hearth. I speak wearing my model engineering hat and some experience!!

[flight1]

well a few things I've learnt for silver soldering apart from practice as posted earlier is,  build a hearth to work on from Vermiculite sheet. clean where you need to braze well (stainless wire brush/emery/ pickle in citric acid etc) . have a precision flame on your torch . don't try to apply the silver solder before parts are both up to temp, you melt the solder with the parts to be soldered not the torch flame!

For small parts I apply a bit of liquid to the area i need to solder then dip the part in the flux powder which sticks only on to the wet area  (spittle I found to be very good for this) then solder.  And importantly after wards clean the parts well to get the flux off by placing in hot water for 15/20min and then polishing /brushing off.

there are other things to look out for too.

[Tim Kearsley]

Hi David, I hope you're well?  We haven't seen you for a while.  OK, all noted.  I've done a huge amount of sold soldering, but just electrical work in the main.  My blowtorch is butane, which I think is not so hot.  Still adequate do you think?

[Tim Kearsley]

Don and Flight1 - thanks chaps.  Comments duly noted.

[David Holland 2]

Butane will be fine, Tim. Don’t get too hung up on the cleaning, abrasive bright is good enough. A plunge into cold water while still hot (not red hot, affects the temper) will shift most of the residual flux and a wire brush should get rid of the rest. Holidays, grandchildren, too hot and generally busy have taken their toll but I am hoping to fly tomorrow.

[David Holland 2]

Ps. Correction fluid is a good way of stopping the spelter going where it’s not wanted!!

[David Holland 2]

Pops. Easyflo is a lot less troublesome than Baker’s Fluid in the corrosion stakes!!

[David Holland 2]

Pops?? Try PPS.

[Tim Kearsley]

Thanks David, all noted.  I should be there tomorrow too.

[Mike T]

Re the hole in the horn.  Make it with a punch if you can.  This will 'dish' the hole in which the solder can pool around the wire.

[Tim Kearsley]

Good point Mike, thank you.