cudak888 

So it was you, rustystrings61! That's the photo that inspired me to try out the propeller shaft method. Thank you! I

Also, I see you're living up to your name

Mike wasn't available last weekend, I'll probably see him on Monday and get you some scraps to practice with.

Given all the recreational smokeums in Colorado, "Crack Corrector" could have many other connotations

-Kurt

dedhed

torsion bars as well.
https://gm.oempartsonline.com/oem-pa...hoCP3cQAvD_BwE

AdventureManCO 

Very kind of you sir. If you get a shipping quote on a box of this stuff, let me know and I'll cover it so you're not out anything! I've been doing lots of research, picking up some good tips. Lot's more to do.

Plenty of meanings depending on one's persuasion - hopefully the right one would be clear if we met face to face haha. In 6mo I'll probably be ready, and the Crack Corrector will be lighting up (a torch)

cudak888 

Well, now I know where the torsion bars from my B-body Plymouth are going if I (finally) swap those worn things out eventually. Prices have gone through the roof for them recently though ("Damn Superbirds!").

-Kurt

AdventureManCO 

This is completely awesome and I'm going to see if we have any large rooftop (HVAC) blower wheel shafts sitting around the warehouse that were returned that I could snag for this purpose in case I ever needed it. I think we have one back there right now, but It is probably too thick to slip through a 1" threaded size headtube.

himespau 

Sometimes you've just gotta caveman things.

cudak888 

Caveman crash require caveman repair.

And sometimes some finesse on the frame table. But usually caveman repair.

-Kurt

BFisher 

I love threads like this. Moral of the story: Yes, lurker/noob/hobbyist/commuter/enthusiast, you can fix your own bicycle, and you should try it.

Sure, dedicated alignment tools in the right hands will always give more precise results, but that isn't always available to everyone, or at all times, increasingly less often with the old time bike shops disappearing. With a little ingenuity, maybe sometimes a bit of finesse, maybe sometimes a bit of brute force, you can get your bike back to an acceptable degree of performance and functionality.

dddd

A solid barbell bar might also serve well.

EDIT: ...seeing that Schweinhund already alluded...

Bergz

I clamped a bent sideways frame to a wooden workbench and heaved on the unsupported part hanging over the edge, Got it straight (I think it had been backed into in a garage) Some DIY wooden frame blocks and a tiny amount of filler and you would never have known. Steel is so forgiving...

gugie 

Uh, yes, yes they are, unless my material science professor was lying to me 35 years ago.

Stiffness is the same on all steels (in case you don't believe me). Strength varies significantly within different steel alloys.

Schweinhund

Steel is an alloy made of iron and any number of different metals (chromium, manganise, molyebdenum, vanadium, etc..). iron is stiff, and has the highest shear strength of any metal. iron is also brittle with a tendency to shatter. alloying agents are broght in in differing percentages to change the characteristics of the finished metal.
This is what my machine shop teacher taught us.
I think maybe you misunderstood your teacher.

bulgie 

BTW your statement that "steel is an alloy" is only true for alloy steel. Plain steel (which is most steel) has only iron and a small amount of carbon, no other metals needed.

Also your statement that iron is stiff is wrong. Young's modulus of gray cast iron is less than half that of steel.

Can you point out where gugie went wrong? If you are talking about his statement that all steels have the same stiffness, we can quibble about a few percent difference here and there, but as long as you add a "very nearly" in there, then it's true. The modulus does vary by about 10% among steels, but the difference is less than that among those commonly used on bicycles and most structures.

Stiffness doesn't change at all with cold-working or heat treating, and only a small amount with alloying or carbon content, excluding some weird or special-purpose steels. BTW stainless has a bit lower modulus, but it's generally considered a separate category among engineers and fabricators.

Do you disagree with that? If so, please try to show a reference.

cudak888 

^
Word to the wise: Metallurgy and the science of materials is wonderful.

...but if you just need to straighten your gaspipe, just go for the first solid rod that doesn't bend on you, and you should be good.

(Seriously trying to keep a straight face after reading that again, but that's another story).

-Kurt

Mad Honk 

Kurt,
If you think this is fun, just come on over to the carbon fiber discussions on the golf shaft forums. It doesn't compare to the ones about steel tubes and the way they are made today. Frinstance, does the weld line create a spine in the tube and can it affect the way the tube works as a spring constant due to the weld temperatures. CF discussions go along the same path and the engineers and designers are rarely asked for opinions. TBH I think steel tubes do have a spring constant and it can influence the way a bike frame flexes during riding, but that is again a theoretical discussion. Smiles, MH

Schweinhund

Not going to argue, you are incorrect and it's not my job to correct you. Or would you like me to go all in and say that you are full of it?

gugie 

"Never wrestle with a pig. You'll both get dirty, and the pig likes it."

I'm 100% sure that I'll never be able to convince you that stiffness of steels is pretty much the same regardless of alloy, I'm just hoping that others that read this will have this is the takeaway.

Since you're not willing to have a reasonable argument outside of "my high school shop teacher told me so", the best option I think is just to put you on ignore.

gugie 

daka

I'll go on the record and say Gugie is right about Young's Modulus. I studied it at school, I've looked it up, I've seen the charts. But Young's Modulus is pretty strictly defined - a coupon of material is put into the machine, tension is applied and the change in length measured. Young's modulus identifies the change in length from where the material will still return to the coupon's original length. It measures elasticity up to the point of yield. Yield can mean several things - the coupon can deform (not return to its original shape) or it may do very little of that and just snap - tensile failure.

Where folks, myself included, get confused is equating this measurement of elasticity with stiffness. Most of us think of stiffness as resistance to bending, but that is not what stress-strain testing reveals. When we bend something it is more complicated, part of the material is under tension and a similar amount is being compressed. The shape of the sample can have more to do with stiffness than the material - with the same mass of material, a tube will be much stiffer than a rod. With a piece of flat bar it will be much "stiffer" when stressed in the plane of one side vs. the other. Taken to a logical extreme, if you fold a piece of paper correctly it becomes rigid enough to support a brick. It is easy to reach a conclusion that one steel is "stiffer" than another.

To return to this thread on cold-setting, which in itself implies that Young's Modulus is not involved since we are deliberately deflecting the material beyond the point where it will return to its original shape, what we are really talking about here is the yield strength of steel - which, unlike Young's Modulus, varies a lot according to alloy and post-treatment. Introducing a permanent change in shape of a mild steel bike frame will require tangibly less force than performing the same ritual on a 531 frame. The yield and tensile strengths are way different. This would be even more evident if the tube sections were identical, which they seldom are. The whole purpose of using high-strength tubing is so that less material can be used for an equally robust frame and weight can be dramatically reduced.

I apologize to those of you who already understand this very well, but given part of the exchange above it appeared that a re-visit was needed

bulgie 

LOL, finally something we can agree on!