Tubing size transitions

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I've got some 3" tubing and I want to turn the end of it into a cone so I can transition it down to 2". I know I can just cut out triangles from the end, fold them in, weld the seams and grind smooth. Is there a trick or mathematical formula for finding out just how much to cut out? I could just eye ball it but I'd rather do it somewhat more precise
Reply:Well, 3" dia will have a circumference of 3 x 3.14 = 9.42        2' dia will be                                2 x 3.14 = 6.28The difference is 3.14 inches.You could take that amount and split it up over however many divisions you choose.The "triangles" you choose to cut out will have angles determined by the number as well as the length of cut. You also need to determine your length of taper for the above itemHow are you going to cut the tubing?  You also might want to make a mandrel to hold your 2" dimension while you are welding.Last edited by dunemetal; 12-24-2011 at 07:22 AM.
Reply:I'll probably cut out the sections with a cutting wheel on a dremel. Tubing is stainless so a mandrel would be a good idea to keep it from walking when welding.
Reply:Might want to also check out a method used , at least in the past, called orange peeling (I think). This was used to close off an end of a pipe similar to what you want to do except the triangular sections (peels) were welded together in a hemispherical shape instae of a taper. Math should be similar. Maybe an old pipefitters text would tell.Good luck.here you go:http://www.fabeasypipetemplating.com...eel-piping-capLast edited by dunemetal; 12-24-2011 at 03:54 PM.Reason: linky
Reply:I think I 'd do the math, on the size of the pie pieces to cut out, like dunemetal suggested. Then I'd make the pie pieces a little bigger, so the small end turns out a little smaller than the other tube, and then trim it back until it fits right.Ian TannerKawasaki KX450 and many other fine tools
Reply:Excellent idea with the orange peel. I'll definitely look into it, thanks! 4130, you make a good point. Rather than trying to make the cone end exactly at 2" diameter, trimming it back would be easier and cleaner.
Reply:Hey derilious,As a suggestion, you may want to try a muffler/exhaust tube shop. My bro' builds race engines & he has tubes done like that for certain applications. There is a fellow he & I use for our exhaust work that has a hydraulic unit that does just that....tapers the larger dia. to a smaller dia.. It does lengthen the tube a smidgen. You may want to check your area for someone who also has that type of unit. My bro' said Greg only charges him $5 to do any size he needs. Definitely worth it & would save you a bit of messin' around....DennyComplete Welding/Machine/Fab. ShopMobile UnitFinally retired*Moderator*"A man's word is his honor...without honor there is nothing.""Words are like bullets.... Once they leave your muzzle, you cannot get them back."
Reply:If it were me, I'd make a simple taper. Even if you don't have a set of rolls you can form it on a mandrel with a mallet. Attached Images
Reply:I tried a few muffler shops and most didn't have tooling sturdy enough for .065" wall stainless. The ones that did weren't able to make a sharp enough transition because the tubing would buckle.Tinbasher, can you explain a bit how I would roll a cone like that or point me somewhere to read up on?
Reply:The pipe fitters handbook (mine is currently at work, sorry!) has the formula required for fabricating reducers, both concentric and eccentric, and orangepeels. Seems to me that would be a good spot to look .In the mean time Try this.
Reply:Great link slow6i, thanks!