jimmuller 

...if a frame could stand straight. Or rather, if it is bent and needs straightening.

I received a frame, mid-80's Centurion Elite GT, in the mail a few days ago. I just measured the rear DO spacing to be 109mm. The right side chainstay appear visually to be bent inward. It may have happened in shipping. The frame wasn't expensive, shipping was more than half the cost of the frame itself. I contacted the seller, but shipping it back to him seems silly. The question is, can it be saved? The bend appears to be centered around where the stay was indented inward to make room for the chainrings. If the metal doesn't seem cracked there would it tolerate being bent back into place?

3alarmer 

...I have successfully straightened frames that were farther distorted than that. I have also broken a couple of frames in the attempt. Not certain there is any hard and fast rule on this. One of the benefits of working at a bike co-op is that you get plenty of experiments to work on....for free, more or less. But if this is part of your dealing with some guy you don't know on the issue, and you have any investment you'd like to protect, you're better off taking a pass at least until the mechanics of the financial fallout are arranged before you make the attempt.

All in all, gaspipe and other similar hi-ten steels are the most forgiving, butted chromoly takes more oomph to reset it (but it generally wants to go back to the way it was), and the newer hi zoot, larger diameter steels tubings are the most troublesome to straighten. Stuff like Reynolds 753 will bend back, but there's some question about whether it's a good idea. Guessing thaqt's some sort of Tange frame, so worth an attempt.

gugie 

^^^
This.

Salamandrine 

You should be fine. Straighten it. Tange #2 is essentially 4130 and is reasonably ductile. Plus that isn't too far out of alignment. If it was early Prestige I might worry a bit. That stuff was brittle. But it isn't.

nlerner

I have one of these for that purpose. You're welcome to borrow it, Jim.

rhm

Wait. Does any steel really want to go back to the way it was? I mean, disregarding the idea that the steel had desires or cares about anything, but does it indeed have any memory? My understanding is that working steel hardens it. When you bend (straighten, adjust, whatever) a frame, all the bending happens within a very small area on the frame, and the rest of the steel remains unchanged. The area that actually bends will get harder ("work hardened") and therefore harder than the surrounding area. So when you straighten it, the straightening will actually occur in the area adjacent to the area that originally bent.

Repeatedly bending the same work hardened area will result in metal fatigue.

So, to answer OP's question: it can handle some bending, but after that, it will break.

jimmuller 

Thanks. I may take you up on that offer if I can't find an easy way to deal with this. It's early in the playbook yet for this to work itself out.

jimmuller 

Well, I managed to straighten the frame this evening. Not too hard, actually. I lay the frame on its side, supported the HT, stuck a long stick (actually my broom-handle hiking stick) inside the rear triangle with one end resting on a pad against the ST, supported the back end of the stick on something high off the ground (my wheel truing stand), then pressed down on the ST so as to lift the DO w.r.t. the frame.. The rear triangle was springy of course so the hardest part was guessing what it would be like when I let up on the pressure. When it measured out to be a twinge under 126mm I stopped. The stays on that side now look straighter. I haven't run a string from HT to DOs yet to measure the spacing but various visual clues look very good.

I was surprised at how easily it bent back into place though I'm sure normal riding doesn't place that much lateral force on just a single pair of stays.

3alarmer 

...I know it seems like you're explaining what happens, but bending a Chromoly stay once, inward, does not in my experience "work harden" it. And also (IME), a stay like this on the rear triangle does seem to have some "memory" (for want of a better word) as to where it was originally positioned in brazing the frame together. I've always assumed it has something to do with the rest of the rear triangle that attaches to the stay itself. All I can tell you without some kind of material analysis is that they do seem to go back into place pretty easily.

,,,the defense rests.


.

gugie 

I'm tempted to employ my mechanical engineering degree and experience here and do some geeksplaining, but let's just keep it simple, and use an analogy.

If a frame has 9 lives, I'd venture to guess that this bend used up one of them.

Pics or it didn't happen? I posted this last year, a picture of a frame I received from @Stevensb:



15 minutes in the Atelier using the same tool @nlerner posted earlier about, and viola:



That, folks, is what they mean by "steel is real".

jimmuller 

Thanks for the pic. Obviously yours happened. I didn't take any pics so obviously mine didn't. But it also didn't look as bad as that.

gugie 

Bad Lag

Things I have learned over the years.

If it is creased or cracked, it's toast.

Any plastic deformation will work harden the area.

You can bend it back to its original shape but it is not the same as it was.

Work hardening causes the area to be stiffer (also known as harder) but also to be stronger.

Fatigue life is used up when cold working the material. It may still have adequate life remaining but some of its capability is gone.

gugie 

^^^
That's a pretty good layman's explanation.

Chuckk

You can use Sheldon Brown's spreading technique to move the triangle back into location and center it.
https://www.sheldonbrown.com/frame-spacing.html

verktyg 

@gugie and @Bad Lag

I received a NOS Motobecane frame from an eBay seller in France. I went into great detail as to how to block the rear dropouts and fork. I even sent him pictures.

https://www.flickr.com/photos/282672...57625469349057

When I received the frame the box looked like gorillas had a party with it. The DS rear dropout was protruding from the really cheap cardboard.







When I took it out of the box, both sides of the rear triangle were crushed together from 126mm down to 95mm.

I took it to a frame builder friend of mine's shop to get his opinion. He put it on his layout table and was able to easily realign the rear triangle. The main triangle and fork blades are Reynolds 531 but the rear triangle is standard Motobecane gas pipe tubing so it was easy to bend back to shape.

I hit the seller up for a substantial refund!

How simple would it have been to block the dropouts and use a more substantial box???

Back in the early 70's when bike manufacturers were pushing bikes out the door as quickly as they could box them up, we ran into quite a few new bikes that we had to spread the fork blades and or rear triangles to get the wheels in. Some came from the factory that way while others were damaged in shipping do to poor quality packing.

The gas pipe tubing was soft and bent easily the first few tries but then it would work harden and get stiffer.

My best bicycle tool investment was a set of Campy dropout alignment tools. I bought my set in 1975 and use them on every bike that I work on.


verktyg

gugie 

To misquote Tom Tolbert's ex-sidekick Ralph Barbieri (yeah, I gots me some Bay Area roots), several things are equally true:

1. The quality of cardboard in France is merde. I'm addicted to eBay France, and it seems that half of what I pay for shipping is to accept some Frenchman's garbage used as packing material
2. I block dropouts with a 2x4. I've cut several at 130mm, a few at 126mm, and a coupleof 120mm with my chopsaw lickety split. Deck screws and fender washers hold them in place. I use two on the drive side, one through the dropout, one through the deraileur hanger. I guess the wood equivalent of a 2x4 costs several Euros, whereas they're scrapwood here.
3. eBay people aren't always the sharpest knife in the kitchen. When you do find a good one, however, try to do as much business as you can with them. Develop a relationship. I've got one guy that I can sometimes talk into taking delivery of a "no US shipments" and forward to me for a fee, and they know how to pack properly and get a good Colissimo shipping rate. My wife calls the guy Jean Valjean.
4. Steel is real! The fact that you could save the frame shows that a bent rear triangle just ain't that big a deal.

jimmuller 

All this has made me curious about something. What DO spacing have been used in the past, besides the garden-variety 120, 126, and more recent 130, 135?

nlerner

I think a more important question is, how much wood can a woodchuck chuck if a woodchuck could chuck wood?