Easiest way to copy angles from an exhaust to make another?

  1. paul r Member


    I havent been on here for a while as I've got married and been really busy over xmas!

    I started TIG welding last year as I wanted to make up some exhausts....I'm going to pick it back up this week again. I made a Jig last year for the original exhaust, so I have a template to make sure it will fit correctly onto the car.

    My question is:

    Whats the easiest way to copy the engles off of the bends of the original exhaust and replicate them with pre bent pipe?

    Is it best to start with the flange on the jig, weld the first straight piece of pipe onto it and then get the bend right for the next piece of straight pipe?


  2. paul r Member

    Guess i'll have to use trial and error then!

  3. knoba

    knoba ...break a leg!

    Sussex, England
    Congrats on getting married! :whistle: :laughing:

    Subsequent exhaust sections would normally be tacked up in situ, underneath the car.

    You mentioned a jig (for a 3d structure?). Any photos? They always help a thread get noticed. ;)
  4. pedrobedro

    pedrobedro Man at Matalan

    CX Derbyshire
    You could bend some coathanger wire along the back of the pipe you want to copy, similar to making templates for brake piping.
  5. Rick Member

    Its very difficult.

    What I struggle with is, you spend as much/more time making the jig than the piece, and you can't normally charge for the jig. For this reason I avoid it. Unless its a run of more than 1 and the jig price can be included.
  6. Ianclapham Member

    North wales
    if you know a friendly plumber who uses 1 1/2" pvc solvent weld waste pipe, used for sinks, you could borrow a selection of bends from him and purchase a length of pipe to cut up between bends, the fittings can be fitted and removed without damage and then the only cost would be the length if pipe, about £4.
    i have done this many times and it works well.
  7. StockEngineer

    StockEngineer Rolling Stock Engineer

    London, UK
  8. hotrodder Member

    SE England
    It's not always possible or at least practical. Even if you have a huge selection of mandrel bends to hand you often find the OE exhaust uses different CLR and/or bend angles to what's commercially available, at least at sensible prices.

    Everyone i know that does this sort of work will make something that fits the car. Whether we're talking about a decat pipe or a complete system it's easier and faster to make something that fits the car/rest of the exhaust system than to try and replicate the OE part/system exactly (but in stainless or whatever). Typically this is done mostly by eye albeit with the origional part for reference using the techniques already mentioned. If we're talking quantity (say a bunch of decat pipes for a club) then you use the first production piece to make a jig AND keep/make patterns used for the first job.

    Obviously depends on the complexity of the part but a jig can be difficult to get right- hands up who's bought a pattern back box for the daily driver only to end up cursing GSF (or whoever supplied the thing) while struggling to get the POS to fit properly!
  9. paul r Member


    Sorry I've not been around, my little boy has had a couple of ops, so i've been busy.

    I've already made the Jig - i'll get a post up later. It's more a case of getting the angles right as I cut the new pipe, I'm just not sure how to do it and get it to mate up square...

  10. paul r Member

    Ok, well I have the jig, how do I make patterns so I can easily replaicate the bends after the first attempt?


  11. hotrodder Member

    SE England
    What's needed in the way of patterns will depend on the complexity of the part and reference points included in the jig...

    Picture a part which has bends in several planes. If the jig only references the two flanges then you're screwed unless the pattern is an actual part (or a perfect replica). On the other hand a relatively simple part may only need a list of cutting measurements if the jig incorpoates suitable reference points

    This really is a case of how long is a bit of string. For sectioning mandrel bends the best way to get repeatable cuts will depend on the tools being used i.e. cutting everything by hand with a hacksaw or angle grinder then a simple full scale drawing and a bit of marking out will do the job. Depending where the bend is being cut can make use of a simple 'pipe wrap' to give a cut line. A bit more work but a homemade mitrebox can make repeat cutting a no brainer. With a verticle bandsaw can make use of fixtures to guide/hold the part in the correct orientation, not as easy to use this method (especially safely!) with a chopsaw though as there's the issue of holding the part securely without the fixture interfering with the saws motor casing during the cut
  12. paul r Member

    I see....I'll get a picture of my 'jig' later for you to see :-) I'm sure some people will laugh! I've bolted the flanges of the original pipe to a piece of sheet either end and then I ran a piece of sheet metal(5mm wide) along the original pipe and welded it on little stalks on a base plate.

    so basically I'm left with a jig that looks like a rolercoaster, following the lines of the exhaust and bends.

    It will become clear when I've put a pic up :)

  13. chimpface Member

    Hi , To find out angles of bends just buy a digital protracter/angle measurer . You can get a good one of a ebay for about £35 - the big chunky looking old fashioned ones .
    I used to make exhausts for F1 and we just used to draw around sections of tube on sheets of paper and measure the angles with a normal protracter .
    Hope this helps.
  14. skrall

    skrall Member

    London, England
  15. paul r Member

    Right, this is my jig!
    • jig2.jpg
  16. paul r Member

    It basically follows the line of the original exhaust with a plate to mount the flange to and a holder for the end of the pipe.

    I've just welded the flange and reducer together tonight and bolted it on the plate.