Duct, Stove Pipe - adjusting elbow angles

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I think this is a Math/Layout topic; if not, feel free to park it wherever.Duct, Stove Pipe - adjusting elbow angles?Wise me up, please.When adjusting for the installed angle of this type of duct:

...is there a more logical method than to just rotate the segments until  the assembly ends up at "about" the angle desired?As I spent about  20 minutes of trial-N-error  "thumbing around" two elbows that needed to be located precisely to match with their connecting duct, I couldn't help but think that there must be a more systematic way  to adjust the angle.

I could have solved a Rubik's cube easier than it was for me to get two elbows and their connector aligned and matched for length.

I  marked a line over the length of the joint so I could at least monitor how far I had rotated each segment, but since I didn't have some  grasp of how a segment's rotation affects the overall angle, the mark wasn't much help I figured if anybody knew, they'd be found on Welding Web.Okay, 90 and 180 degrees are easy enough.But, does anybody have an intuitive  trick or maybe some rule of thumb for achieving other angles? Thanks in advanceLast edited by denrep; 12-11-2013 at 10:58 AM.
Reply:I remember my dad pulling his hair out when he was doing the same thing. I only heard about it over the phone, but never questioned it again. Simplest jobs can drive you insane sometimes.I hate being bi-polar it's awsomeMy Heroes Have Always Been Cowboys
Reply:My take is since it has three segments to rotate = 90 degrees, each segment individually is 30 degrees.Does that help?(I always just use my eyeballometer though)

Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:No doubt close enough for a cold Minnesota night...  

But not exactly, because simply turning a segment takes the assembly out of plane. In other words, with an out of plane  assembly, although possibly adjusted to the desired angle, if placed on a flat surface the inlet and outlet will be at different heights from the flat surface; creating an angled off-set of sorts. Although sometimes that may be desired, I suppose.I have a feeling that the O-fficial method is to counter-rotate the segments to split any adjustment  between them, thus maintaining the center-line.Next time I have to fly I'll try to get one through security so I can give it a few hours of in-depth study.

But yeah, they're basically a stack of triangles, or wedges, so it'd seem that there's gotta be a real basic MO for it.Last edited by denrep; 12-11-2013 at 12:36 PM.
Reply:Ah, you want finer adjustment then the 30 degree segments.I have not tried it, but suspect you are correct on the counter rotations to keep the same plane.Try a 1/4 rotation on two of them and measure the angle you get - you are probably right.Yeah, when it's cold out, 30 degree angle is likely close enough to smack it with my hand and make it fit

Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:4 segments.  22.5 degrees each.Yes, you rotate them in pairs with each half of the pair being moved in the opposite direction.
Reply:Btw, I think you should use JEGS harmonic balancer degree tape from a Chevy 350 on all three segments and report back your findings



Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:

Originally Posted by rlitman

4 segments.  22.5 degrees each.Yes, you rotate them in pairs with each half of the pair being moved in the opposite direction.
Reply:But when moving equal-and-opposite isn't it just the differential of moving two rings that can be calculated? It would seem that moving a third and fourth would cancel the effect?

Unless third and fourth were moved at a different rate, which would bring off-sets into play?


Reply:

Originally Posted by denrep

But when moving equal-and-opposite isn't it just the differential of moving two rings that can be calculated? It would seem that moving a third and fourth would cancel the effect?

Unless third and fourth were moved at a different rate, which would bring off-sets into play?


Reply:you need two identical pieces to keep then in the same plane
Reply:Adjusting elbows are for cheaters. A Tin Nokker wouldn't need em.Just cheat, like I did. get em in place, stay warm and have a Merry XmasBTW cut a new hole in the roof if you have to.That's kinda what I did.
Reply:

Originally Posted by tackit

go to a corner of the house, roll the sections so the fitting touches both walls.
Reply:

Originally Posted by tackit

go to a corner of the house, roll the sections so the fitting touches both walls.
Reply:COOL !!! THREE YEARS LATER YOU GOT IT .






  Some things do take longer than we think .


Reply:

Originally Posted by BD1

COOL !!! THREE YEARS LATER YOU GOT IT .






  Some things do take longer than we think .


Reply:never move just one segment.  It helps if you can put a couple foot long piece on both ends of the elbow for eyeballing purposes.My name's not Jim....
Reply:http://www.efireplacestore.com/fsd-bm0023.htmlIf you do not mind a little extra creosote build up this looks like the elbow for you haha. A bit pricey though. Sincerely, William McCormickIf I wasn't so.....crazy, I wouldn't try to act normal, and you would be afraid.
Reply:They do make a five piece galvanized elbow, that has four joints, in heavy wall pipe. Then you can make even plane 22.5 degree turns. Sincerely, William McCormickIf I wasn't so.....crazy, I wouldn't try to act normal, and you would be afraid.