how to counteract warp in welded tubes-

[fairchild1934]

So i'm working on the rudder horn and i have enough warp that it won't quite go onto the post.

I thought I remembered B-Spot saying he used a mandrel inside while he was welding to fight the distortion.

If I do that-- will I end up the the mandrel stuck-- and I have to beat the part off-- and ruin it in the process ?

I expect the hinges to warp the same way if I do nothing----

Do you have to heat the part some to get it back off the mandrel (to expand it ? )

I will have more of those types of parts to go on the feathers --- so any hints/experience shared might help out a lot !!!!

Thanks ahead of time--
Tim

[Camflyer]

Eric's manuals go into detail about how he did his. They are worth the money. But if I remember he cleaned inside the tubes before welding. And used a mandrel

[ScottS]

I don’t remember any warping just that if your welding is to hot it will leave a little bead on the inside, I used a file on the inside in a few spots. Scott

[fairchild1934]

not really a file problem. The tubular part went from round to a bit of a triangular shape. An interior tight fitting mandrel is the only thing I can think of----
I'm sure this is from asymmetrical expansion and contraction as the bead is going down.

[Steve W]

Are you using the proper size tip for the thickness of metal? Are you welding the entire joint at one sitting or 25% at a time? Watch the penetration when welding straps to tubing like the hinges. Angle your tip more when the puddle starts and avoid spending too much time in one area so you don’t over heat and penetrate to the other side. A little different thinking here than say a gear or wing root fitting where you want deep penetration. Tip size matters specially if your trying not to overheat the metals with too small a tip.
I don’t have my plans handy. It’s been a while sense I built the rudder horn but isn’t the male tubing piece necked down from a thicker stock to insert into the rudder spar tubing? Even if you welded it all at one sitting to the flat stock, it would seem hard to me, to get that much distortion.
I cut off the flat stock from my rudder horn and welded on a thicker piece this past winter to accommodate a better shaped bar for the amphibious steering set up. The male part didn’t change shape and went back into the rudder tube without any trouble.

[Steve W]

I meant to mention that I found when welding anything regardless of the type of joint, DON’T do it all at once. 25% at a time. Tubular butt joints, cluster joints, tube to flat stock joints etc, allow some cooling before continuing. You lessen the chance of the entire joint being heated to the point of where it will distort. Cluster joints and heavy welded parts need to be stress relieved when completed. My 2 cents. AND this is all gas welding.

[fairchild1934]

I was using a .040 tungsten and trying to do a pretty small weld. Probably a bit on the hot side as I think my gas coverage was perfect-- noticed the weld was a little grey and not like bright mercury. often time when the bead is a bit dirty-- you get a bit too much heat because the bead isn't flowing as good as usual. I switched to a gas lens and that helped the puddle.

The tube that the horn is welded to is only about .001 inch larger than the rudder tube. So -- ANY-- distortion is going to mess with you. BARELY slide on before you weld. It could be that i need to do more tacks to help stabilize the part more before making the final big momma weld.

yes- gotta get up with Eric and order the wing and fuse. manuals. More help is better :-)

Tim

[Steve W]

Ok. Your Tig welding. I can’t help you there. The basics should be the same. I’ve tried it but have to many “bad habits” from many hours of gas welding.

[fairchild1934]

OK--- I think I got it nailed ----
went to a gas lens 1/16 red tungsten. about 15 CFH .045 rod for tacks and 1/16 rod for welds.

I put the solid mandrel into the tube (interference fit)
tack 4 tiny as possible tack on each end. Let cool. Then 4 more tacks on each end .
Then I welded up each end----about 3/8 of bead at a time and stopped to let it cool.
By the time I was done I could still slip it off the mandrel. It slid on the rudder tube about 90 % of the way right off.
I tweaked the ends just a dab in the vice (there was about .005 diameter differential- and it slid on and moved all most completely freely.
a little interior polishing with a couple of grits of paper with my finger -- and its good to go...
May polish it with a cratex wheel inside - maybe. Will post picks later today.

The mandrel helped a TON. No inside texture or burn through. The gas lens helped too-- as the puddle was cleaner and flowed as it normal beautiful self. Highly recommend the mandrel technique. (turned id down in the lathe from a 1 inch rod. )

Tim

[alaskabearhawk]

There is a specific sequence in welding tube structures to minimize or eliminate warping. This is especially true when welding the fuselage clusters. I found this book to be extremely helpful: https://www.actechbooks.com/0218-VEX-B.html

[fairchild1934]

Thanks ABH--- but I got that one about 4 months ago. great book !