Clevis to stainless steel tube?

[davidleitch]

I recently had to install a clevis onto a thin stainless steel tube used as the elevator control rod in a molded plane. I eventually did this by gluing it in place, and then following some advice by drilling a 1 mm hole through the brass clevis and the stainless steel tube and inserting a 1mm piece of wire to act as a pin.

That's given a good result but I just wondered how else to do it? I certainly wasn't able to solder the tube and of course it couldn't be removed from the fuselage as it was connected to the elevator bell crank.

I'm told a number of molded planes use these tubes for control rods so I guess there must be a standard way and I can't believe glue will do the job.

[davidleitch]

Photo shows the pinned linkage. You can see the pin in the far servo if you look hard enough.

[davidleitch]

deleted

[Tuomo]

My planes have mostly come with carbon pushrods. It is quite easy to glue fittings to the end of such pushrod.

But why cannot you solder the fitting to the end of metal pushrod? Just clamp the pushrod with small pliers in front of plastic outer tube -- this will take the heat somewhat away. only then attac the well cleaned pushrod end with hot soldering iron and do it quickly. I have done similar jobs with good succes.

[Jurgen]

I wonder if you distort the stainless steel tube abit in the end that disappears into the brass clevis's sleeve (making a dent in it, making a little hole in it, grind or file a little grooves or slot in it, pinching it) then the solder (or epoxy) will follow this distortion. This can guarantee that the steel tube will hold on because the distortion will not permit displacement even when the bound capacity is not 100%. You can extent this by making a distortion in both steel tube and brass clevis's sleeve, this way aplying the remedie 2 times at same bound. But if you solder, then solder to brass would be very dependible and not needing the remedie for distorting the brass sleeve, then only the steel tube distortion might reassure you. Maybe you did this already, why worry then. Just my thoughts.
Jurgen.

PS zero: what Tuomo said, most important, distract soldering heat to a good contacting iron clamp before the plastic sleeve, you dont want to melt that. No issue with epoxy instead of solder.

PS:making holes (like for your pin) and exaggerated filing or grooving will be weakened points, dents do not weak the material this way. Be sure that your pin is far enuf in the brass sleeve! The pin will fill the hole but not it's induced weakening of the material.

PS bis: roughning the steel tube (by low grid sandpaper) is a less powerfull means of increasing holding power but in the end it might be enuf, but why take chances? Distortion will give more guarantee.

PS2: if using solder you might use extra separate solder flux to the steel to improve bounding. Make sure you have enuf soldering-heat available (i think 75watt as a minimum and a fat tip with large contact surface) as too little will compromise the bounding strenght. Do not use fast soldering gun types for this as even with 100watt their little tip has not enuf heat accumulated potency or heat inertia, even when glowing they cool down too fast. A good soldering bound looks smooth and shines, with too little heatpower u cannot obtain this.
Next week we go on with: "soldering cactusses on your mother in law's forehead" :D

[Jurgen]

Another important warning, if you do not have serious experience with soldering like this, dont make your expencive plane as the first practice. Take some remainders of brass tube and steel rods and practice on them, and make a destructive test on them to see how strong your work was. Same for epoxy! When in doubt, make a similar simulation and pull it apart to convince yourself of succes or failure. Nothing worse than flying scared unnecessarily.

And clean/roughing the inside of the brass clevis or practice tube! For expoy and even more for soldering. Its a real invisible boobytrap !

[Salto]

David, I think that pinned joint should be fine, but for future reference, soldering this thinwall stainless tube and small brass sleeve would be straightforward. There's only a small thermal mass so any medium sized soldering iron would be adequate.

The brass will tin and solder very easily, and as long as you use an appropriate flux the thin wall stainless tube will also tin and solder easily. For stainless steel I've used hydroflouric? acid as a flux, but I've also seen commercial preparations. Plain flux cored solder, or plumbers flux will not work on stainless steel.

Stainless steel is a bad conductor of heat, and the tube is thin walled, so if you pull the tube as far out of the plastic outer as you can (maybe disconnect the clevis fom the horn at the other end), and you're quick, it shouldn't melt the outer.

Graham.

[davidleitch]

Well thanks for the advice guys and particularly to you Graham. When I experimented with a small piece of the tube I couldn't make my normal sold take even with an 80 watt iron. Perhaps it needed better preparation.

I am totally satisfied with the pin, and actually will probably do it that way if there is a next time.

[raschow]

In my experience, "Stay-Brite" silver solder kits sold in hobby shops work fine for soldering to the SS tubes. Expect the included zinc chloride/hydrochloric acid liquid flux is the main reason for success. Clean joint area thoroughly after soldering with water or rubbing alchohol to prevent later corrosion. Good Lift!

[Salto]

Perhaps it needed better preparation.
It just needed the correct flux.

Graham.

[DrFragnasty]

For stainless to mild steel/ brass, use silver solder (BOC gases...around $25 for a pack of 5 rods) & a 50 to 70 watt iron or a needle-point butane soldering iron. Get the silver solder flux too.

I've got the same arrangement on the Escape...tried (naively) to use standard solder 'til advised by my guru, Bruce to use silver solder.

Insulate the bejesus out of the surrounding area however or set fire to the fuse.

Don't ask how I know ;0)


regards,

Chris.