How to align pipes

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Neighbor asked me to weld two 45s on the ends of a 2.5" pipe.  For what its worth, its thicker, maybe schedule 80, stainless.This isn't rocket science, but I would like everything lined up as close to perfect as possible.  He specifically said he wasn't going to polish it, but I'd like to line things up as if he would.  This is for outside appearance - I'm not worried about the inside.My problem.  How do I determine a centerline or a witness line on the 45s?  They are so small that I feel that any mark I make will be heavily influenced by any imperfection on the welding table or even imperfections in the tube itself.  There is a line were the pipe has been welded but I'm not sure if that is usable or not.Also, is there a trick to finding the center of a pipe?  The straight section will be about 4' long and I've seen tools that find the center on pipes.  I don't have such a tool but I figure there has got to be a trick that I can do with a T-square (T-square and a plumb bob?).  The 45s will be weled to each end of the pipe and I would like the exits to be on the same plane.  My table, although pretty flat, is not big enough to hold everything.  The only tables I have that are big enough are relatively warped wooden topped ones.BTW, I usually buy 90s and mark them, then cut them.  These 45s are 'dinky' small.Con Fuse!Miller Dynasty 350Millermatic 350P-Spoolmatic 30AMiller Multimatic 200Hypertherm PowerMax 1000G3Miller Maxstar 200DX
Reply:If putting them together on the same plane (two 45's to make a 90) I will lay them flat on the table. Rolling them back and forth you should be able to find the exact side of any bend.  I have also layed bends on the cement floor before and slid them back and forth a few times to "scratch a line" in the exact side of the bends.
Reply:All you need is a table with a nice flat surface. Cut the miters and before you bevel the ends, lay the pieces on the table holding the ends together and roll the pieces around until the profile matches. Then make marks to ID where they line up. Then bevel the ends and weld it up.Ian TannerKawasaki KX450 and many other fine tools
Reply:If you are looking to make it more fun then go ahead and put on the first 45. Then set your pipe in V blocks and shim the blocks to exactly level the pipe.  Then put a level from the pipe to the outside of the 45. Rotate the pipe until you get your level plain and clamp it down.  Savy???   Now take the other 45 and line it up on the other end using the level as you did before, retaining the level plain and mark it, clamp it, whatever blows your skirt up.Then put at least three fusion tacks on it and re-check alignment. If all is well ZAP away.
Reply:Are you talking about cutting 45* miters on the end of the pipe and welding a mitered 90, or are you talking about welding on two 45* weld els? Big difference, and at the time very similar. For either it is not critical that you know the c/l of the pipe. Either lay it on a welding table or level it up in pipe jacks, level the weld el up and tack, level the other side up and tack.  I think you may be over-thinking this, it is not difficult. You don't usually need the C/L until you are putting on more fittings, or need the distance between two legs, or are changing planes.
Reply:Old thread ---Re: Finding center line along the length of a piece of pipehttp://weldingweb.com/vbb/showthread.php?p=255276Lincoln SA200's... at least 15 - 20. They come and go. Growing partial to the "Short Hoods" in my old age. Last count on Short Hoods was 13 in possession.
Reply:What will this stainless pipe be carrying?Remember, when you tig weld an open root stainless joint, you need back purging to prevent sugaring (porosity) on the inside of the root.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:double postJasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:Thanks for all the hints and suggestions.This is going to be a 'nerf' bar on a jeep.  The brackets already exists (mild steel) and the guy has tons of the stainless laying around.  He did buy pre-cut 45's.The 45's will go on each end.As for welding.  I'm going to cheat it a bit.  I'm going to bevel it 1/2 way.  Maybe a bit more.   3 or 4 tack welds, then autogenously weld the first pass.  Fitup will be very tight (except for the bevel of course).  Subsequent passes with 308L filler, just to fill up the bevel.   I have some polishing belts that will knock down the weld if I let the beads get too high.  Maybe 180grit flap wheel if I really need to work it.Hmmm, maybe I will back purge it.  The weld is going to be so close to the edge of the pipe that the tape will melt/burn off in short order.... those 45's look to be a small radius.On the back side of the weld there will be a visible crack.  Mostly because I will not have full 100% penetration.  But the weld will be plenty strong as it is - the rest of the jeep will rust away long before the step/nerf bar does.The bracket itself will be put on with 309 filler.As for the centerline on the 45s.  I think what I'm going to do is roll it on a flat table (steel one).   Roll it one way, mark the middle, roll it the other, mark the middle again and split the difference (if there is one).   For marking the middle - from hobohilton's link - use a square with a bubble level.  The bubble level will make sure I find the top, the rulled edge will let me measure to 1/2 the distance.Con Fuse!Miller Dynasty 350Millermatic 350P-Spoolmatic 30AMiller Multimatic 200Hypertherm PowerMax 1000G3Miller Maxstar 200DX
Reply:I've always found it a pain to have an extra argon bottle and regulator/hose for purging. I prefer to use Solar B weld flux for back shielding the inside of stainless weld joints. Much more convenient in my opinion. This would be the case for you as well.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:I actually I have a double output flow meter (two separate flow meters on one bottle).  Normally I do the math and purge 6x the volume.  On stainless pipe I typically use aluminum tape.  The one thing about aluminum tape is when it gets hot it gets greasy and will fall off.  The glue gets the consistancy of motor oil.   I have used masking tape, but that gets brittle/ burnt/burns etc.  Usually requires a bit of cleanup.  Now that I think about it aluminized tape + a band clamp could work.I have a 20 year old can of solar flux.  Not sure if its any good.  Just the pricing of solar flux seems a bit high (which is why I got the other flow meter and not a new can of Solar Flux).  I guess I could try it.BTW, the Smith dual output flow meter was by far the cheapest. Cyberweld has it for $170ish delivered.Con Fuse!Miller Dynasty 350Millermatic 350P-Spoolmatic 30AMiller Multimatic 200Hypertherm PowerMax 1000G3Miller Maxstar 200DX