Hello everyone, I wanted to ask everyone how far tubes can be squeezed. and what role does the wall thickness play? To what extent does this affect stability? Or will the tube be weakened?
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Do you have more details on what you are trying to do? Toptubes? Chainstays? Material?
Here is a good thread:
All chainstays are “ovalized” by a forming press:
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The 30 x 16mm chain stays that most tube suppliers sell start life as a 24mm OD tube, so that degree of ovalization is a good place to start if you’re looking for a rule of thumb. I’d be reluctant to do more than is absolutely necessary, though. This may be one of those things were the eye test is a useful guide, i.e. if it looks like too much it probably is too much.
When I’ve experimented with ovalizing tubes, the centers will crease a bit if you go too far and don’t use a form to control the shape. Something like the image below. Depending on how the tube is painted/illuminated this could look pretty bad, imo, but I’m not sure it’s any worse structurally.
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Kris at 44 squishes his to flat and seems to have success with his chainstays. I try very hard to design without the squish but sometimes a tweak here and there is needed.
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want to squeeze a 0.9mm wall thickness OD 28.6mm tube down to maybe 18mm. My plan was to print a forming press with the 3D printer. Check the fitting and maybe mill it out of aluminium.
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@Daniel_Y On your trip to Taiwan, were you able to see whether the manufacturers stress relieve tubes after forming (bending/dimpling/ovalizing), or complete frames after welding? I’m assuming they do this at some point (probably after swaging/butting?), but thinking about it some more 24mm OD → 16x30mm oval + dimple would really be quite a lot of cold work.
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For steel, I am pretty confident they don’t do any stress relieving. I asked why they don’t heat treat the entire frame (to normalize the HAZ), and our guide told me that people have tried in the past, but the frames warp too much during the heat treatment process.
With regards to stress reliving individual tubes, I don’t think this happens either. The coldworking is used to strengthen the tube. A conversation with Fairing (tube manufacturer):
Regarding the 31.8x.8/.5/.8-600mm tubes, the mother-tubes (blank tubes) will also reflect the hardness. For example, to make this tube the factory has to start with the next biggest size, 34.9mm, and draw down to spec (I forgot how many passes but at least two because for each butt). BUT if 34.9mm tube is not available or a shortage, they would use the next biggest size, 38.1mm. Using a bigger OD will make the tube a little harder because of more drawing down needed to get to spec. And yes, they have to anneal tubes prior to cold drawing to spec.
Summarizing: Tubes are annealed and then cold drawn. The cold drawing work hardens the tube to achieve its final strength and hardness. Depending on the raw stock size, some tubes will have more cold work (and are harder).
This was the chainstay press from Maxway:
It was interesting was the adjustable dimple:
The floor manager would double-check and fine-tune the dimple before every run and compare to the 1:1 drawing. I saw a kinked dimple nearby, so I wonder if there is some chainstay-to-chainstay variation that requires adjustment. Or maybe that was just the initial run?
For titanium, totally different story. I still need to learn more about it.
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Thanks for the info! It is fascinating to see production tooling, it is totally different from what custom builders use. I started to doubt my initial recommendation after noticing that the Dedacciai Zero Uno catalog describes most of their tubes as stress relieved, but if the Taiwanese manufacturers do without it there’s no reason to be too concerned.
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This is an interesting find. The factories I saw formed their own chainstays in-house in production, so maybe they avoid the stress-relieving step out of practicality and cost savings.
In my experience, the CS dimple carries the highest risk. It seems like the factories have empirically found the optimal dimple and ovalizing shape to reduce that risk. This is just speculation (I can update the thread if I find out more), but they probably use thicker gauge steel or plain 4130 for chainstays to improve the workability and reduce risk.
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Rather than pressing, I used to form 1500mm long aluminium flat oval by manually pushing through a set of parallel, but adjustable width steel rollers several times.
Home built at almost zero budget when I started the company (Hacked Black and Decker Workmate with some steel shelving angle and two used conveyor belt rollers), but it lasted over 20 years and processed over 1000 tubes.
1.5 x 0.049" (also up to 0.065") cold-drawn seamless 6061-T6 formed down to 40 x 88mm approx flat oval, so just over 2:1 fineness profile.
This gave a really good, flat-sided and round-ended section, without the central crease or a pointed crests that are typical of pressing.
In my experience, this method has far less effect on the material strength at any single spot than a single pressing does, since for each successive pass through the rollers, a different area of material is slightly deformed…essentially, the flat spot starts out at the top edges of the tubes, then gets progressively pushed outwards as the tube deforms.
All the best,
Dan Chambers
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