Maybe there is a chemist on this list who chime in...

I am setting up my new Angel's Shadow, using a new technique on the pull pull rudder, although used my many others. It involves using a through hole (hollow) 2-26 brass threaded coupler. The cable (steel U control) is fed through the coupler, then looped back in for a tight fit. Then the inside of the coupler is filled with solder. I then used a Hayes clevis to attach the cable to the rudder horn. This is a very clean installation.

I did this last weekend, and a few days later, I noticed one of the clevises had "broken off" right where the threaded coupler ended in the clevis. I looked at the other side, and just touching it, the clevis broke in the same way, the plastic sleeve portion of both clevises were brittle, and crumbled in my fingers. I can only think of two explanations:
1. The clevises were very old, even though I had just purchased them last week form the local hobby store. I have used these for many years with never any kind of problem. They have a metal pin and a very firm closure.
2. Either the flux I used (Stay Brite) or the solder caused some chemical reaction with the plastic.

Any other idea, or similar problems?

Dale

I'm just guessing, but you may have had voids in the solder fill, which led to the brass coupler failing in fatigue.

Im no chemist or soldering genius, but I do know flux contains acid (muriatic) of varying amounts that if not cleaned off will attack metals and I assume other materials. I believe isopropal alcohol to be the solvent of choice here.
good luck
Jim

it wasn't the brass coupler that broke, it was the plastic clevis, they just fell apart...

May sound like a dumb question, but did you put the plastic clevis on the threaded part before or after soldering? If before, the heat from soldering might've compromised the plastic.

not a dumb question, but no, I did not solder with the clevis on.

In that case, I have but one other suggestion which is to echo one you made earler, that they are from very old stock.

Others have more expertise in these matters - of that I am certain - but soft plastics have solvents in them that make them pliable and over time the solvents evaporate and they become brittle.

At least you still have the model in one piece![sm=thumbs_up.gif][sm=thumbs_up.gif]

Most fluxes available today are not corosive ( EPAgets into everything ) Even so in the electronics industry we use nylon hardware all the time and have no issues. I doubt the solder or flux had anything to do with it. My guess is that they were heat damaged. Either the brass had some residual heat still from the soldering or the clevises were a tight fit on the coupler and enough friction was generated to create enough heat to damage the plastic. You could just be right and they were old but Ihave never run into that myself.

Most plastic clevis's are made from nylon6-6 and this material dries out over time and gets brittle. Back when people used nylon props they were told to boil them to rehydrate the nylon every so often.

Dale,

Any binding at all in the linkage setup? I know you are smarter than that but with that clevis, what did you use around the clevis as safety to keep it latched? Perhaps it got moved when you cleaned the plane or something and caused it to bind a bit. BB clevis's are the way to go if you can IMO.

C

Dale, has the clevis ever had raw fuel on it. I had an experience a few years ago with a transmitter that accidentally got filled with raw 30%. Before I could get it apart, the plastic around the sticks crumbled and the sticks fell out of the transmitter. 30% nitro will destroy plastic in a hurry.

Joe Dunnaway