Pipe Nesting...?

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A buddy came to me with a project for "later on," involving three nested pipes: a 4" diameter one, a 4 1/16" diameter one, and a 4 1/4" diameter one. All are 1/16" thick. The 4 1/16" one is going to have cutouts, and the 4 1/4" will be in two strips at the top and bottom. I'm not entirely sure what he wants it for, but I told him to come back in a bit once I'd done my research.First question- how the L am I supposed to weld three nested pipes together like that? I haven't been able to find much documentation on nesting pipes- only joining them. I know the outer pipe is going to be a lap joint at the bottom of each strip, but I'm not sure how to deal with the top.Second, could I do it with stick (I'm guessing 3/32" 7018, or maybe 1/16 if I can find it) or should I TIG it? He didn't seem too concerned about slag entrapment in the cracks of the pipe, but it seems like something that could be an issue someday.Third, he asked an obtuse question about cutting the finished pipe-wich in half across the diameter of the pipe, with a chop saw. Good idea, bad idea, run for the bunker because the CWO said to "hey, watch this stuff"?Currently working as a Paralegal, but still interested in hobby welding.Miller Bobcat 225ntOne- Character Fractions: ¼ ½ ¾ ⅛ ⅜ ⅝ ⅞
Reply:What's he building...a Battlebot? I'd tig or mig them over stick welding them.Is the final cut lengthwise or perpendicular to this creation?If lengthwise, they could be cut with a plasma cutter or a cutting wheel on a grinder.Please post pictures when completed...Rich
Reply:My guess was a space fighter, so that's as good as any.From what I gather, he wants to cut the pipe-wich into two semicircular halves.
Reply:Just to get technical for a moment.You'll have 1/8" diameter increments in pipe if they are 1/16" wall thickness. Then lots of grinding and polishing to get them to actually fit together smoothly.With all thicknesses like those, TIG would be the best choice.Be wary of The Numbers: Figures don't lie,. but liars can figure.Welders:2008 Lincoln 140 GMAW&FCAW2012 HF 165 'toy' GTAW&SMAW1970's Cobbled together O/A
Reply:I'm just thinking outside the box, but coul you guys cut, thread and use bushings? Something similar to galvanized water pipe or gas pipe? Just a thought. Pidge.Lincoln210mpHobart Handler 125...soldBoat battery and a couple coat hangers
Reply:I have 'nested' pipes like that before for used in heated applications (asphault / tar ... the inner pipe carries the tar and the outer pipe carries heat oil so the tar doesnt cool off and clog the pipe)Never with sizes that close though ... did a lot of 90s and branches .... build the inner pipe first then slid on the outer pipe and flanges in whatever order makes it possible.So to your questions of how to 'nest' pipes i answer:  carefully with lots of forethought and perfect fit up.AWS CWI xxxx21711968 SA200  Originally Posted by WelderMike  I hate being bipolar, It's awesome.
Reply:Originally Posted by mike837goJust to get technical for a moment.You'll have 1/8" diameter increments in pipe if they are 1/16" wall thickness. Then lots of grinding and polishing to get them to actually fit together smoothly.With all thicknesses like those, TIG would be the best choice.
Reply:Originally Posted by teh603Right, looks like I did my math wrong up there. 4", inside 4 1/16", inside 4 1/8". Something like that. So the pipes just won't nest that smoothly?
Reply:Originally Posted by mike837goDouble and triple check your math before going to the supplier. Remember that you have 2 'walls'. Think that each wall increases the RADIUS of your pipe. But they are sold by diameter (d=2r).Then we have manufacturing tolerances. Extruded copper pipe will have nice, smooth, tight tolerance inner and outer walls. Cast or forged steel? Not so much.You'll have to carefully get rid of whatever finish (mill scale, paint, powder coat, etc.) that was used to keep the stuff from rusting.Were you going for a fit-up that was telescoping antenna like? Or much looser.
Reply:Years ago, I dismantled a telescoping antenna from a walky-talky.The tops of each section were rolled in to reduce the diameter to a snug fit against the next inner section. So that it had a friction fit of an area equal to the wall thickness, while the gap between sections was at least .010"The bottoms has small copper leaf springs/bushings to guarantee electrical conduction for the full length and to prevent pulling the inner section out the top of the outer section.As you say, sloppy is in the eye of the machinist. Fitting pistons to cylinders or fitting tires to wheel wells; Same rules, different tolerances.Be wary of The Numbers: Figures don't lie,. but liars can figure.Welders:2008 Lincoln 140 GMAW&FCAW2012 HF 165 'toy' GTAW&SMAW1970's Cobbled together O/A