I finally talked this guy into selling me his early 70's Raleigh professional. It's an awesome but pretty beat down. One of the issues was a monster dent in the top tube.

IMG_4006 by frankthewelder, on Flickr

I had an idea a while ago to plug the ends of the tube, fill it with air pressure and heat the dent. It worked well. It was pretty scary though


IMG_4008 by frankthewelder, on Flickr

and after a bit of clean up.


IMG_4011 by frankthewelder, on Flickr

tapered tubes pressed in the vent holes and held with a wedge.

The heat had to affect the properties of the tubing. I have to wonder about the integrity of the top tube now.

Maybe, but the damage isn't at a location that gets much stress. I don't think this is a problem.

Nice work, Frank. Do you know how much air pressure it required? Did the dent pop back into place, or was it a slow process?

Dang, I love me a man that can FIX stuff!

You are quite industrious, your projects always amaze me.

I think I remember reading about a builder that was using hydraulic pressure to pop out dings. In any case, nice job.

The risk is not knowing where the real weak point is! The material around the dent is work hardened with a potential result being a blow out somewhere else! I too am curious about the process, how hot, how much pressure, etc.

I've read of people filling the tube with water and then freezing it by putting it outside in cold weather.

Brilliant manoeuvrer! I've gotta tuck that away in the back of my head. I'd love to watch a video of that.

Given that it's winter here, I would have filled the tube with water and put it outside to freeze.

Would this method tend to pop out only the dent - or try to expand elsewhere as well?

I used about as much heat as one would use brazing a fitting with about 100 PSI of internal pressure.

When tube is manufactured it is heated several times. The drawback of what I did was simply alter the "condition" (temper) of the material. The tube had been seriously compromised with dent with a depth of nearly 20% of the total diameter. You could tell it liked what I was doing when it went back to it's original position. Now it is at least round and straight. If the frame was crashed hard, it might fail or more likely bend at that location along with the rest of the tubes. I am pretty sure this is a lot more predictable than the freezing method ( I have repaired several split tubes also). Is it as good as new? No. Is it still a good 531 frame, Yes. Will it crack? No.

+1. ftwelder, you are amazing! Can you show us how you set this up? What you used for the plugs and how you get 100psi of pressure in there?

Wow! Cool idea! I agree, heating the tube in this manner is unlikely to seriously affect the strength of the frame, especially where this dent was located, and considering that there was a dent there in the first place. Other repair methods that have been successfully used for 50+ years, like replacing or splicing the tube would arguably be as, if not more, detrimental to the integrity of the frame than this method. Also, when this frame was brass brazed originally, the tubes were almost certainly heated to a higher temperature than ftwelder did here.

Nice!

Dave

ftwelder, Thanks for the explaination. Did it "pop" or slowly take shape and why didn't it exceed the original diameter?

I wouldn't use freeziing water approach, as the tube might split somewhere else instead!

Dave A, I would agree (not that my opionion has much merit). Splicing woudl be an awful approach in my mind! However, isn't replacing the tube at the lugs be OK? If you can find equivalent DB 531.

I'll add my voice to the choir here, that is impressive.

Yes, Replacing to top tube is OK, for sure, and is the most often used method of repairing damage like this. However, the old tube has to be removed and a new tube installed. This is a fairly labor intensive process, especially on a brass brazed lugged frame, and also involves heating tubes & joints. You also have to be able to get the new tube back in place, which often means reaming lugs and opening holes in the head tube and/or seat tube to the full diameter of the top tube. While this isn't necessarily a problem, structurally, it does alter the original nature of the frame, to a degree, which is not always desirable, especially on a classic or collectible frame.

Thanks!

Dave

I love seeing ingenious repairs like this. You probably just saved that frame from the scrap heap. Between this and the rolled-top-tube-dent of the Austro-Daimler a couple of months ago, it's just what this forum needs. way to go man and thanks for sharing

That might have made a good youtube video.

Be fun to see a straightedge against the tube now from various angles, what is visually straight is not always actually straight. I think the approach was sound considering the damage. That tube was tweaked visually beyond just dented. I would check the overall alignment of the frame now.

The problem though is some, many? frames have stresses built into them, cold set straight. If this frame had stresses that the heat was going to allow to reveal themselves, a much different result might have happened.

my technium has a quite big dent on the downtube i am kinda scared !

When John says this is okay we should all take it as being okay...