cold setting.
 

So, I have cold set my Gazelle frame to 130 mm (from 120). As I was a bit strapped for time the first day i worked on it, I only spread it 5 mm. When I came back the next day it had gone back to 120mm. I was immediately surprised but then the duh moment kicked in and I realized this steel has been at 120mm for 35 years. So, I spread the thing all the way out to 130mm the next day and popped a wheel in to keep it from going back.

The question is, am I not spreading it enough to get past the 'memory' the metal has or is this just the way things are? Do I need to over spread a bit and bring it back?

The way it went back, I'm worried that my alignment won't stay right.

I've cold set a lot of frames and I've never had that happen. You think it bent itself back overnight? That's pretty ridiculous, don't you think?

unless a herd of mice in the basement came along and bent it back, yes.... it crept back overnight.

I have set a half dozen frames or so, some do seem to be "more springy" for lack of a better term, than others.

You need to compensate for the springyness with overstrech. Once you release it it should stay where its at.

Springyness is one thing. Bending back overnight is another.

Maybe your ruler shrunk overnight. It's no less likely.

+1...Cold setting, by definition, means you bend the frame. Not flex it apart, but bend it. A bend in steel will stay bent unless you bend it again.

So what do you think did happen, assuming the OP's observation has some truth? Or are you saying it has no truth?

i can assure you, there was no error in measurement. Such things are kind of my job....

I think the OP's second paragraph is not describing a frame that's been cold set (permanently bent), but one that has only been flexed apart. When cold setting a frame, you have to flex the frame well beyond the target spread in order to actually bend it.

sounds like i need to pop the wheel out and see if it goes back again. If so, I didn't actually bend the frame....

sounds like the ol' warm set imo.

+1

Assuming I merely flexed the frame apart rather than bending it, should the resultant return to its original size have been more immediate? Several measurements were taken in this process over a 10-15 minute time frame and it didn't return to its original spacing during that time.

Something just doesn't jive here. It doesn't matter at this point anyhow. Try again.

You can ask over on the framebuilding forum to get an expert opinion. The little I know is that steel is elastic to a point before it yields. Ie, as someone else mentioned, you need to bend it (push it past the yield point) or it will just spring back. How fast it springs back seems to be the question here as you didn't truly cold-set your frame by pushing it past the yield point or it would have stayed bent. At least it works that simply for something like a flat steel bar. Once you add in the structure of the dual set of rear stays and brake bridge, etc maybe something more complicated is going on.

Wow, this is an interesting thread. It seems to me, too, that if the frame was merely "flexed" it should have sprung right back once the "springing" force was removed. I'll be interested to see if we ever figure this one out.

I'm taking the wheel out in about 5 minutes and will measure through the course of the night and see if it goes back.

How did you cold set the frame? Sheldon's method? All-thread, nuts, and washers? Some other method?

It shouldn't make any difference. Bent is bent.

Of course. But as has been mentioned before in the thread, there seems to be some uncertainty as to whether the frame has actually been bent (cold set) or merely flexed apart and a wheel jammed into the dropouts. I guess what I'm really asking the OP in post #19 is "did you actually cold set the frame or did you just put a wider-than-the-dropouts hub in it and expect the frame to permanently stay at that spacing?"

And to the OP, I'm not trying to be a smart alleck, just trying to help you figure out what's going on with the frame.:)

"Gazelle - the frame with the spring in its giddyap!"

-Kurt

Anything remotely resembling steel will, at room temperature, spring back instantly to a final shape once any external stress is removed. If the final shape is not what is desired, apply stress again in the desired direction of deformation and release (no need to hold for any period of time). If the final shape is not as desired, repeat the above process until the final desired shape is achieved or fatigue cracks start to appear.

if it really was bent to 130, and then overnight relaxed to its previous dimension, that means that there were some residual stresses close to the yield stress that pushed it back. It just doesn't sound like the way that steel acts. It does seem like aluminum will do something like this though. Given the smooth curvature of the aluminum stress/strain curve, it seems more likely in that case.

Alignment
 

Be sure that proper chain alignment is maintained when the rear triangle is spread to your desired width. In other words, if the frame is currently at 120 mm, aligned correctly to begin with (not always the case) and you want to go to 130 mm, you need to spread the right side 5 mm to the right and the left side 5 mm to the left to maintain proper alignment. If the entire 10 mm spread is achieved by setting only one side of the triangle, the chain line will be off. Spacer washers on the rear hub and/or funky rear derailleur adjustments will allow some compensation, but it is always best to start with an aligned frame. And align that rear derailleur dropout too (Park tool DAG-2).

Bob (who wishes he had a C&V nickname like all the cool guys do)