Flex Cable Soldering

How-to Article ...by Rudy Hilado

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Step-by-step instructions on how to solder a flex cable...

 

Having difficulty soldering that flex cable to the brass ferrule? It isn't as difficult as you think, as long as you start with the right flux and solder. Here is a step by step guide on how to solder a flex cable to a brass ferrule. This is how I personally do this procedure. There are many other variations and techniques, but I've found this works for me and I haven't had a single solder job fail yet. Click on the first picture to step through process in detail.

Experiment with the process and have fun!

 

 

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I've found the most important ingredient for making a successful solder is the flux. I've tried many different brands and types of flux, and the Stay Brite Stay Clean flux has been the only one that works. You will save a lot of frustration by using this flux. See the main article page for information on where this flux can be purchased.
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The other components for making a good flex cable joint is using the proper solder and the right torch or heat source. Use a good SILVER based solder. I picked up this Oatey Silver plumbing solder at the local Home Depot. Often soldering is difficult because too much heat is used. A nice micro torch like this one from Harbor Freight puts out enough heat without burning off all the flux.
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Before soldering the flex cable tip should be cleaned. Many folks go through very elaborate processes to clean the tip of the flex cable. I've found that this really isn't necessary, since the Stay Clean flux does such a good job at cleaning the cable. But I would recommend just running a wire brush over the end of the tip, all around the cable to clean off any grit and grime.
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If the cable is really greasy, you can use some acetone to clean it off. Dip it in the acetone then wipe it off with a rag or paper towel. Allow the acetone to evaporate before proceeding, or you'll have a little eternal flame at the end of your cable as it burns off the acetone.
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I would recommend firmly holding the cable in a metal vise for soldering.
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Soldering a flex cable will result in excess solder dripping off the flex cable. I use a metal bucket under the vise to catch any dripping solder.
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I start by soaking the tip of the flex cable with flux. You'll notice that the flux starts to clean the cable as it soaks in.
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Cover approximately the first 1 inch of the flex cable with flux. It's ok if a little of the flux drips off.
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Heat up the cable the with the butane torch until the flux starts to boil a little.
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Once the flux starts to boil, start rubbing the solder against the flex cable tip until it starts melting.
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Keep periodically heating and soaking the solder into the flex cable. If the solder doesn't soak into the cable and just runs off the cable, stop and go back and drip a few more drops of flux onto the cable, while it's still hot. The flux will probably immediately boil off (don't breath the fumes!), but start heating again and apply solder.
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Repeat the heat, solder, flux application until the solder is dripping off the cable.
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Loosen the vise and rotate the cable so you can soak the other side with solder and flux.
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Once the entire tip of the flex cable is soaked with solder and flux, leave a little extra solder hanging on the cable and move on to preparing the brass ferrule.
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Make sure the prop shaft is put in the brass ferrule first. This will prevent the flex cable from being inserted too far into the brass ferrule. Put a drop of flux inside the brass ferrule. In this picture, this ferrule has been used before so it already has a coating of solder in it. If you are using a new ferrule, cut a 1/8 - 1/4 inch piece of solder and drop it in the end ferrule.
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Heat up the end of the ferrule to boil the flux and melt the solder. Rotate the ferrule as you are heating it to let the solder coat the inside of the ferrule.
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Press the ferrule up to the end of the flex cable and start evenly heating both the flex cable and the brass ferrule until the solder starts to melt.
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Press the ferrule up to the end of the flex cable and start evenly heating both the flex cable and the brass ferrule until the solder starts to melt.
 
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Once the ferrule is fully seated on the flex cable, let the work cool. You may find extra flux and solder on the cable and ferrule. After the work as cooled, go back with the torch and heat up the flux and extra solder until it just starts to melt, take away the torch and then wipe off the excess using a folded up (many folds) rag or paper towel. Be careful not to burn yourself. I'd recommend wearing leather gloves. You should end up with a nice, clean solder joint that will not break!
 

 


 

 

 

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