best way to taper tubing?

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I have some 4 in tubing .065 wall that I want to match up to some 3in .065 wall tubing. Its for an exhaust, nothing special just a transition to make a tip fit. It seems as simple as just making slits around the tube and bending it in, but I would like it to come out kind of nice if at all possible. Is there some sort of template i could use to mark these cuts? Or any kind of method that people use on a regular basis to do this. I would prefer to avoid the trial and error.I was thinking taking 4 equal mesaurements around the tube and removing 1/4 tapered to 0 pie cuts out of the tube, this way when its all pressed together i would have nice seams that I could weld up and grind smooth.Last edited by claymans13; 01-04-2012 at 03:16 PM.ESAB MigMaster 275Miller Econotwin HFMiller Syncrowave 250
Reply:Well, I am no expert but circumference of the 3" tube is 3.14" smaller than the 4" tube so you would have to remove 3.14" total tapering to zero.So just divide 3.14 by as many wedges you want to remove to get base dim. for each wedge.I may be tempted to just buy an adaptor that has been formed by a mandril. Good luck.AZ
Reply:Start with a 4" tube about 6" long.  Use a short piece of angle iron, lay it on the tube and scribe a line the length of the tube.  Measure the circumference of the tubing, Divide by 8. Take that measurement with a pair of dividers and mark the end of the tube in 8 sections starting at the line you scribed length wise.  You should end up where you started.  Measure back on the tube 3 or 4 inches and scribe a line around the tube,  Now take the circumference measurement and divide by 4.  Set you dividers for this measurement.  Start at the scribed line that was back 3 or 4 inches and where it intersects the line you scribed length wise and make marks around the tube.  Scribe a line from every other mark on the end back to one of the marks down the pipe. This should make it come out with 4 pie shaped pieces.  Cut out the pies and bend the remaining fingers in till they touch.  Might take a little heat to assist bending at the scribed line.  Then weld it up.  That's how I would do it any way.  You are on the right track.Dan
Reply:I'd get some 0.065 sheet, make a template of your transfer out of card stock or something similar, trace it out on the sheet, roll it into a cone and weld it up.
Reply:Is there a reason that a pre-made adapter won't work? Originally Posted by SundownIIIDon't get me wrong.  They are just as ill informed about politics as they are about welding, they just post more on that subject.
Reply:Originally Posted by jmtebbensIs there a reason that a pre-made adapter won't work?
Reply:Another way would be to fabricate a simple cone of whatever length you need, as Kazlx has already suggested.Make it a bit less than 3" at one end, and a bit over 4" at the other, weld up the single seam, and trim the ends off square to get the diameters exact.This will be a lot neater, as the single seam can usually be hidden, or filed smooth if not.A very short cone is easiest to cut from a flat sheet, after you develop a suitable paper pattern with scissors.A very long cone will be easiest to make by slitting a piece of four inch tube in one place only (at the original weld) and removing a big Vee of metal.  Curl it back up, hold it closed with hose clamps, and weld it up, then grind the ends off square.The welded cone can then be hammered back into shape over a piece of thick wall tube to get it back to being round at both ends.A long slender smooth cone not only looks good, it flows very well too.Last edited by Warpspeed; 01-04-2012 at 11:59 PM.Cheers,  Tony._________________________________Transmig 310 + Argoshield LightOxy acetyleneOxy propanePrehistoric stick welder_________________________________
Reply:Originally Posted by WarpspeedAnother way would be to fabricate a simple cone of whatever length you need, as Kazlx has already suggested.Make it a bit less than 3" at one end, and a bit over 4" at the other, weld up the single seam, and trim the ends off square to get the diameters exact.This will be a lot neater, as the single seam can usually be hidden, or filed smooth if not.A very short cone is easiest to cut from a flat sheet, after you develop a suitable paper pattern with scissors.A very long cone will be easiest to make by slitting a piece of four inch tube in one place only (at the original weld) and removing a big Vee of metal.  Curl it back up, hold it closed with hose clamps, and weld it up, then grind the ends off square.The welded cone can then be hammered back into shape over a piece of thick wall tube to get it back to being round at both ends.A long slender smooth cone not only looks good, it flows very well too.
Reply:you need thomas  franklands book "pipe fitters handbook"but yes you are gonna in this case( 4 x 3) cut   (4) triangles out and leave 4 arms to( heat and)  beat together and weld ..the arms will be 3" long or  little less and 2 3/4" across.. Attached Images
Reply:You don't need to make any cuts.  take it to a muffler shop where they have the machine that bends the pipes and also has a tool to expand the end so you can just fit the other portion in.
Reply:Stainless or steel? I'd use a pipe expander as well.