getting motivated again. hydroforming basics and twisty pipes.

[HeadSmess]

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 up...im 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...)

 

[HeadSmess]

piccies







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...

 

[Deleted member 12676]

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

 

[HeadSmess]

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!

 

[Deleted member 12676]

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

at http://www.ajdesigner.com/phpcircle/circle_arc_length_theta.php#ajscroll
angle = 17.3/(10.35 + 2.35)
= 17.3/12.7
= 1.362 radian (ie 78 degrees)

 

[Deleted member 12676]

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.

 

[HeadSmess]

jaguar...that deserves a thanks.

done.


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.

 

[Deleted member 12676]

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: http://play.tojsiab.com/MENVUm1WT0Uwd2sz

 

[Deleted member 12676]

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.

 

[lazylightning@mail.r]

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.

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)