Steer tube
 

Anybody straightened a bent steel steer tube?

no. Throw fork away and replace, unless fork is very fancy and you want to have the steerer tube replaced (I'm sure at a cost much higher than a new fork) by a framebuilder.

+1 on no. You will never get it straight enough to work properly and you stand a good chance of damaging it's attachment to the fork crown. Replace it.

Also, if the (I assume) crash was enough to bend the steerer, check to be sure the frame's headtube wasn't distorted too.

FWIW, a lot of people talk about the 'predictable failure' of steel - that it does not snap or shatter all at once.

Well, bending is the first step in predictable failure - since it is bent it has failed... If this had been a failure of an aluminum or carbon steerer it may have been catastrophic. The advantage of steel is not that you can (or should) fix all damage, but that after a crash or impact the bike can still be ridden for a short while to get you home... after you get home, though, replace your fork.

The frame is not damaged, and the direction of the bend is the opposite of what would result from a head-on crash. Plus the bend is not near the crown, so there's no reason to stress the crown.

How did it bend if not from a crash? Landing from a jump?

Steel hardens when bent (aka "work hardening"). The hardened area is more brittle than the surrounding steel and acts as a stress raiser. Bending the tube back to straight hardens it again, increasing the stress raiser. The steer tube is hidden inside the head tube where it is difficult to assess for stress cracks. Your fork is the main thing that prevents your face from suddenly meeting the pavement at any given moment while riding. Do the math.

That's possible, but I got it this way.

Math? I think this is hard to analyze. Please explain.

I understand work hardening, but I'm surprised one event , a bend around 2 degrees, is enough to make the next road bump fatal.

simple enough...replace

Structural failure possibilities aside, it's going to be difficult to straighten the steerer with sufficient accuracy to assure the headset bearings align properly.

I have an LBS looking at this - haven't picked up the fork yet, but they say they were able to bend it nearly straight, but did not try to reverse the original bend. Essentially they added a new complementary bend, it should be straighter.

You know, I read English, and I understand what was said. I'm not sure I accept the logic, yet.

Not trying to start a war here.But i dont understand the logic of asking for advice and when you get 100% saying one thing with no detracters, you want to argue.I say replace it,your talking about what keeps your face off the ground man.But its your face.

If you read what I said, I'd like to understand the reasons for the advice better, in concrete tuerms. I got several kinds of statements: Do it, it's safer; Do it, it's work hardened, Do it because everyone just says so.

I tend to doubt that the fatigue accrued in my fork is that great, because the bend area is very small and the tiny kink is very small, and the bend radius is only 2 degrees.

Nonetheless you all say just do what I say?

I'm really sorry I bothered, guys.

Goodbye.

It would take far to long to explain here,and i dont type fast.If your the type to explore this kinda stuff deeper,Google metalurgy.Or however one spells it.Very informative stuff for enquiring minds.
I perhaps mistook your inquiring mind for an arguementive type,but it seems the latter is all too common here.I see you also enquired in frame builders and got same answer as here!
As someone has already said its not like you will see any stress cracks starting inside steer head tube making it too risky, for me anyhow.Probably would have been better to not straighten it out if only 2 degrees.Putting another bend in it just increases risk.

If the bend is minor, it is possible to straighten a bent steer tube using a rod of the appropriate diameter inserted into the steerer. Clamp the rod in a vice, insert rod as far as possible, apply straightening tool to steerer, insert rod farther, repeat until rod goes all the way in. And remember that most steer tubes are butted, so the rod should taper.

As previous posters have noted, this is something you have to be careful with and not all bent steerers are good candidates for this treatment. But I don't see why steerers are different from any other steel bike frame tubes. I have straightened forks and frames, and ridden on forks and frames for years after they were straightened.

If you read my FIRST post, I didn;'t ask "Should I do this?" I asked if anyone has done this, implicitly asking please share your experience.

I can imagine the potential risks as well as any of you. Why would yhou all assume I had not done that? It isn't what I asked.

I know metallurgy somewhat, at least about work hardening, and I've been riding bikes and servicing my own for nearly 50 years - good ones, bad ones, and indifferent ones. I can tell when I have a good mechanic at an LBS, who I can use for the tricky things like this. None of us should have to justify ourselves here.

Maybe you feel vindicated with what the FB's said, agreeing with the BM's. I didn't really see any more informed viewpoints, so far.

Thanks, Sluggo, for discussing at least how it might be done. This fork, being cheap, is not butted, but has a heavy internal reinforcing sleeve extending about 2.5 inches above the fork crown bottom.

My LBS has a full set of alignment tools including some bars used for bending. Plus, no apes work there. Same three mechanics for the past three years, same service manager for around 7. Don't judge my resources based on teh incompetence of your own.:twitchy::twitchy::twitchy::twitchy::notamused::notamused::notamused::notamused:

Glad to hear you have good mechanics.

How did this end up? I took the fork to my LBS, and they straightened the tube quite well. Unfortunately they used an internal bending bar a lot smaller than the steer tube, so the thread end was ovalized by about .02 inches by my caliper. I spend a few hours yesterday squeezing down the oval with a pair of large 14 inch channel pliers, measureing and squeezing at least 15 times. I also de-burred the lip of the seat tube with a medium rattail file and emery cloth, smoothed the top with a mill file, and relieved the stem maybe .001 inch. Result now is that all the headset parts thread on with no binding but some friction, and the stem inserts as far as I will need.

Strength of the tube is now more of an issue in the thread area, but the end is reinforced by the steel headset parts (1972 entry-level bike), so I'm still going to set it up for a test ride. If I like it, I'll get another fork.

If the tube itself is the only part that's bent and provided the bend is more of a bow and not a kink then straightening the tube is entirely possible and won't affect the steel enough to matter. if it actualy kinked the tube right at the headset bearing or due to pressure from the stem or similar then I would toss it. You won't be able to straighten a kink of that sort and have it sized right or to be able to ensure the tube is truly axially straight with home shop tools. But a long radius bowing isn't a biggie to straighten.

Aluminium would be a far different story but steel is far more malliable and something this small would not work harden it enough to generate any sort of danger in the steer tube. Same with stress cracking if it's a smooth long radius bend. But again if it's a very short radius kink then all bets are off and I'm definetly in with the "replace" camp but more due to difficulty with ensuring that the tube remains round in section and difficutly in straigtening that immediate area than for fatigue reasons.

After all, everyone and their brother says it's fine to "cold set" an older steel frame for new wheels. And you can bet your bottom dollar that most times this is done the bending goes past the right point and is adjusted back and forth a few times. The degree of bending for that process isn't any worse than straightening up this steer tube if the degree of bend noted above is accurate.

I'm still curious about the cause of this bend in the tube though. A force that can bend the steer tube would almost certainly have an effect on the legs unless it's because the handlebars got jammed and levered against the frame in some sort of crushing accident? If that's the cause then a kink bend seems far more likely. I'd do some more checking to see if this is the case.

For tooling to do this you'll want to make up some hardwood saddle support blocks. Drill holes of the right size drilled and then cut the blocks to form U shaped supports for both the fixed base as well as the pressure application. A drill press would be my weapon of choice for applying the force with the degree of control needed. But if you don't have one a length of 2x8 used from the edges and a long enough F clamp or similar would work but likely require a few extra hands to hold everything in place as it tightens up. Sneak up on the pressure required to deform the steel back into line with a lot of re-checking. Move the supports around and twist as needed as indicated by the results. A dial guage and V blocks to check the runout for size and location would be a nice setup to have.

If it's an entry level bike it won't have enough alloying metals to make work hardening a problem.
If the bike fits and you are happy with it try it for a while. Be overly cautious with the fork until you get a few hundred miles on it.
I think I would be tempted to replace the fork.

Golly that sounds goofy to me. For a second opinion, try the frame building forum.

I wouldn't worry about the work hardening thing, but that's not the issue. Think about what a steer tube does and how it fits in the headset. I'd think that if the steer tube isn't pretty nearly perfect the headset cones aren't going to be parallel and the headset is going to bind up.

BC, thanks for the insight and encouragement. At this point, my LBS has bent it back, it is very close to straight. They ovaled the steer tube at the threaded end due to bending force, so I think the tech used an interior bar that was way smaller than the steer tube ID.

Yesterday I spent a few hours measuring the steer tube along different diameters, finding the high spots and low spots, and squeezing the ovality out of the tube. I used a 14 inch channel pliers for force and protected the steer tube threads with wood buffers. A fairly small squeeze made a measurable difference, so I made at least 15 small squeezed, adjusting the direction of applied force each time, based on remeasuring the diameters. Finally I was able to thread on the threaded race. Then I focused on inserting the stem, which I could do after a few more squeezes, deburring the threaded end, and dressing the flat end surface with a mill file. Now I can get on the race, washer and locknut, and insert the stem as far as it can go. Today I cleaned the frame and parts, so this evening I'll try installing the balls and the fork. My experience is if a newly rebuilt headset adjusts right, it is functionally right. We'll see soon!

The bike is entry level, probably mild steel in the 10xx family. It's a decent fit, about a cm smaller than my absolute max. That large size (55cm c-c) is why I want to experience it, to see if the older French style of frame design suits me.

What you outlined is my strategy: ride it a little while being careful with bumps and other stresses, and if I like it, get another 40 year old Peugeot fork in good condition.

I really can't see any other damage to the fork. If I'd seen fork blade damage when I checked out the bike, I wouldn't have taken the bike in the first place. I've done some inspection with a straight edge next to the blade to better see a kink, but nothing is apparent to the eye or the fingers.


Retro Grouch, I wrote that post before I had received the straightened fork from the LBS - I was going based on what they said on the phone. Looking at it, they did not zig-zag it in any way. It's just made straight.