getting motivated again. hydroforming basics and twisty pipes.

Discussion in 'Performance Mods' started by HeadSmess, Oct 4, 2015.

  1. HeadSmess

    HeadSmess Well-Known Member

    i need to go get some superglue...another point to procrastinate over.

    dont do it kids, its a filthy habit! just get up and do it!

    been modelling up pipes for the nsr150 the past few days, mainly to try and prove the point that you DONT need anything more sophisticated than scissors, aerosol cans, a blowtorch and patience...

    the aerosol cans might be a but too thin for the size of this pipe, and the number i have to cut just going for a particularly flimsy galvanised toolbox lying around. saves having to prep any joins as well. the point remains the same. its thin enough to cut with heavy duty scissors.

    brazing the majority and welding just the header section...all 29mm of it.

    but, thats irrelevant. the main point of this thread is to lay out some maths required for hydroforming.

    once i have this section modelled up in paper i can squash it and measure all the new angles...

    the basics are simple. start with a straight cone, and the length wont change...but the diameters will be flattened, becoming half the circumference each.

    if you make a cone bent through 180 degrees... you have to figure out what the bend will straighten out to when "flattened".

    figure out how to use a freakin spreadsheet and i could find the relationship between diameters and angles...

    then its no more rolling cones and cutting paper but just lay out two profiles, seam weld, and inflate.

    seriously, using 240gsm paper (stiff) you can go through a full ream before getting to the stinger... amazing how much difference just 2 degrees can make.

    so far it looked like a 36:63/340mm cone bent through 130 degrees flattened out to 56:100/340mm at 90 degrees... unfortunately that bend needs to be expressed as a radius...

    backtrack. (56*2)/pi= 35.7... about right.

    (100*2)/pi=63.7ish.... also close enough...

    i also have to find how the inner and outer radius varies from the main or central radius. thats a function of the diameters/degree of taper... hmmms.

    there is no way im ever going to contemplate spinning one! (trumpets...)

  2. HeadSmess

    HeadSmess Well-Known Member



    stock pipe has a rather abrupt taper on the reversion cone, not to mention the belly is flattened out to gain clearance...both bad things to do to tuned pipes! well, ok, the steep taper only makes it "hit the wall" at 10700rpm. simply cant get it over that point.

    dont really like the way they include a dimple to clear the spring on the rear brake pedal either.

    and apparently.... im not going to cut it open until i have a replacement ready to go though...apparently theres a cat inside the belly! a stinking big baffle! a hindrance!

    now thats guaranteed to do bad things!

    this better be worth it... aiming for 36 horsies at 11k. bit more than the stock standard 27 or so. still not really pushing it either, got at least another 8 or more hiding in there somewhere... removing metal might release them...
  3. jaguar

    jaguar Well-Known Member

    What is each section of your mockup pipe made of?
    Did you ever make the real thing?
  4. HeadSmess

    HeadSmess Well-Known Member

    right. thin cardboard/thick paper. 200gsm or more. easy to work with.

    i got lazy and cut up a 0.5mm galvanised toolbox and just butt brazed :)eek:) the sections with expected results :) it fell apart within two days.

    it was more a test rather than a permanent fixture. already made another pair of different dimensions. faster than welding currently.

    i really meant to cut up aerosol cans and cut little tabs on the ends so i was doing lap joins for the brazing but yes...lazy :) (i forgot to print em out with the guidelines and didnt want to print them again...)

    with max band at 11000 it performed much as calculated...but let me wind it all the way up to 13k, unlike the stock pipe...

    which made for much better take offs in first gear. that few hundred extra rpm is all you need to get a smooth shift.

    wasnt as powerful as i would have liked. possibly two horsies more. not much. i did make it more for a wide band than peak power but, so i guess i cant complain.

    sounded freakin awesome :) oink oinks didnt pull me over...thankfully.

    i didnt do anything as intended regards the maths, but i dont think it should be too hard.

    figure out the difference in radii when one draws out a certain taper through both 90 degrees and 180 degrees, should give the equation needed to figure out other tapers/curves/radii.

    hint hint...spreadsheets, man...;)

    i love this video, it just shows how easy it is... just getting the initial profile...thats the challenge!
    Last edited by a moderator: Dec 15, 2015
  5. jaguar

    jaguar Well-Known Member

    Here's some calculation basics for hydroforming a curved section of header:
    angle = arc length / radius
    so for this exmple:
    angle = 17.3/(X + 2.35)
    angle = 14.1/X
    since the angle is the same for the two formulas we can make it:
    17.3/(X + 2.35) = 14.1/X
    17.3X/(X + 2.35) = 14.1
    17.3X = 14.1 x (X + 2.35)
    17.3X = 14.1X + 33.1
    17.3X-14.1X = 33.1
    3.2X = 33.1
    X = 33.1/3.2
    X = 10.35

    angle = 17.3/(10.35 + 2.35)
    = 17.3/12.7
    = 1.362 radian (ie 78 degrees)
    HeadSmess likes this.
  6. jaguar

    jaguar Well-Known Member

    It's strange to see but when you blow up a hydroformed curve the curve becomes more pronounced. Instead of using trial and error to finally get it right it is best to go through this calculation procedure. This 78 degrees of flat curved section will be 180 degrees when blown up with water pressure.
  7. HeadSmess

    HeadSmess Well-Known Member

    jaguar...that deserves a thanks.


    makes the process so much easier... though i see a lot more number crunching to generate tapers(different radii with different central points)thats the basics.

    try having a go over xmas.

    from what youre saying there...i draw a circle with 10.35, another one with 10.35+2.35, 12.7 radii.

    cut out, weld, scribe lines for the 78 degree marks, leave some extra to inflate and remove at the ends, cut weld n inflate...

    and i should get 180 degrees between scribed lines at 1.5", following a centre line of erm...4.75" radius...

    if this works... i wont be amazed :wacko:

    but satisfied, yes.
  8. jaguar

    jaguar Well-Known Member

    I haven't done any hydroforming myself so there is a distinct possibility of a needed correction factor due to the metal bending.
    I would do a test run to see how off the final product is and from that make a correction factor.
    Look at this video showing the pipe curl in towards itself as its being formed:
  9. jaguar

    jaguar Well-Known Member

    People have used from 900psi to 2300psi to do it.
    But at the lower pressures it looks like the final product is a bit oblong instead of round.
    And at the high pressures the metal stretches about 5% in diameter.
  10. lazylightning@mail.r

    lazylightning@mail.r Active Member

    That's alot of pressure! I've put in an order with the laser cutting shop my friend uses, they will cut the pieces of metal for the cones and belly using 0.8mm stainless steel. I will be hammering them all into perfect shape by hand. The nice part are that they will already be cut to perfect size, so all I have to do is bend them. Hydroforming sounds nice though)
  11. jaguar

    jaguar Well-Known Member

    I think the main advantage of hydroforming is the time savings to make a curved header section. I like to see the distinct sections in the pipe so would probably make the remaining cones the normal way and weld them all together and then to the header.
  12. HeadSmess

    HeadSmess Well-Known Member

    have fun with that ;)

    welding 0.8 stainless is no fun, plus it cracks if its not completely immersed in argon. ie, welding in a glovebox... theres a reason i only made 1 stainless pipe, ever.

    the specific alloy in use plays a part...

    if he works at the laser cutters, that saves a fair wack. local company quoted me over $200 for 20 pieces in 1mm gal. me supplying metal and dxf files. real competitive over here...

    it isnt as easy as it sounds "hammering to shape". sure, works if determined but its a lot of work. better to have lines etched into them for folding on, the more bends the better. you need a special panbrake but thats no major issue. way easier than trying to produce conical sections with a ring roller etc

    the metal stretches and deforms and the perfect profile is no longer so perfect once joined together.

    then making sure each and every weld is square and round (ha ha!), making good header joins so it doesnt vibrate to pieces, blah blah blah yarda yarda.

    ive done enough to think its stupid and hydroforming is the way. or some type of spinning system, like they do trumpets etc. but the same problem arises. welding each section together. its a lot of work! (and if you get someone else to weld it up... expect around 200 or more for that little job. at least 3 hours. if theyre any good...

    the pressure is well within a pressure washer with 10,000psi or so on tap.

    sure, therell be some wasted bits of steel as one gets the fine details right but what jag said there was basically the procedure i was thinking of... even with variations of 5-10% from calculated... the differences should be consistent for a given material at a certain thickness at a certain pressure. not that hard to calibrate for.

    im planning on getting if not a whole pipe in one go, close enough to the mark to make the one or two sectional welds a lot quicker. youll note most factory pipes are done this way, either hydroformed or stamped, and then seam welded only. very quick and cheap.

    at least doing it freeform (no mold) allows for even faster simpler changes to dimensions.

    you could even try making prototypes from plastic sheet or doped tissue paper and seeing how they inflate with air... possibly. worth a shot...
  13. lazylightning@mail.r

    lazylightning@mail.r Active Member

    Hi Headmess!

    I made a stainless tourque pipe before and it was/is great. When riding in the winter, with all those chemicals on the road, the hot header pipe almost rusted through in a two week period once. My next header will also be made of stainless. The header will be connected to docking ports via strong springs, to both the exhaust manifold and the tourque pipe. Otherwise the excessive forces when jumping and riding bumpy roads could break the header pipe, again...
    My friends friend has a laser cutter at work and does side jobs. All pieces cut cost me about $18 US, their metal (0.8mm stainless). I'm hoping everything will be okay with the welds. The main thing is to hang that pipe so that there are no stresses on it. My first pipe was welded by a magician named Nadya, at my old work. She was a 60 year old granny at the time and she has the highest rating of welding experience, went through decades of shipbuilding. Sooo... using the 0.8mm stainless steel sheet I cold forged into perfect pieces, she was able to weld the cone and belly seams and the cones and bellys together using a typical stick weld system with huge 2mm stainless electrodes. There were a few tiny holes here and there, but the JB weld helped just fine. When we were done welding it together, she smiled and told me that no other welders in Moscow could have done that for me, and that it was all because of her skill. I had no doubts. Whenever she raised hell about someone in the buying department having supplied her with electrodes that she deemed unfit, she always got things straightened out. Such welders are highly praised. After each cone and belly was done, I would clean off any metal that dripped through to the inside before joining it to the neighboring cone. She did it for free, spreading out the whole job over like two weeks, so our boss wouldn't get sore too.
    This time however, I have gotten alot of my own experience in welding thin stainless sheet, using TIG. One of the most important factors I have discovered is not only the proper settings, but using a thin donor electrode. Dropping big beads from a 2mm rod screws things up in a really big way because the huge heat you need to melt and spread that fat bead is more than enough to put a hole in the thin walled stainless sheet right next to it. A 0.5mm donor rod is even good on thicker sheet. By making all the edges meet perfectly so no light gets through allows one to weld the seams without using a donor rod almost all of the time. That's how I plan to weld this one. After each tack weld is placed, the edges should be corrected so everything stays right on. After several tack welds are in place, it aint going anywhere and you can just go around and melt those edges together. There are some TIG machines at two of the shops I can go to and use the equipment and I don't have to pay anything since they owe me money =-)
    Yeah, pounding those cones into perfect shape is a long and tedious process. Two or three cones a day is more than enough. No need to stress oneself. I understand that the seams will be done on a seperate day and then on another day I will weld those cones together. No need in me getting on people's nerves by sitting down on the TIG and trying to weld it all at once. Besides, once you get tired, the results of the welding can vary greatly...
    I had thought about making a form for a tourque pipe from solid steel, from two peices that squeeze the metal sheet in between them using hydraulic pressure. The thing is, it should be a popluar pipe that many people need, to justify all the work in preparing such big and heavy steel molds and a hydraulic pressing setup for it.
    When you mention typical pressure washer, do you mean like the small Archer models (on wheels), easily moved by one hand, or do you mean some kind of special car wash industrial unit sized thing?
  14. lazylightning@mail.r

    lazylightning@mail.r Active Member

    As you can see, I made my first torque pipe out of an old stainless vat I found laying in the garbage by my apartment building. I used an old IKEA office chair shock absorber thing as the round anvil surface for pounding and a large hammer. It looked nasty after it was first welded up, but then I cleaned it up a bit and it's just fine.

    Attached Files:

  15. lazylightning@mail.r

    lazylightning@mail.r Active Member

    Here's my new stainless steel gas tank. I made it out of scrap stainless sheets of varying thickness. The gas cap is a wonder of engineering. I made it have three levels inside. Each level connected by a small hole and with a spiral labyrinth in the first two levels. There was supposed to be a small airlock screw that I could close when I'm not riding to prevent fumes from leaking out, but I didn't get it done before my trip to Crimea last summer. So once when I had a full tank, the thing fell over on it's side in the little vacation house and since I was on the other side of the room and my hands were full, it took me a whole four seconds or so to pick the bike up off of the floor. Not even a single drop spilled out! On the road it's great, no drops come out from the bumps at all. It hold's exactly 2.0 liters.

    Attached Files:

    Last edited: Dec 13, 2015