Here is an ongoing diatribe of my writings about titanium.
Disclaimer: I try to keep it organized by topic but it’s fairly futile. Someday I’ll make it a logical document Until then, good luck deciphering.
Why Titanium Bicycle Frames?
October 1, 2012: Interview: Andrew Bernstein, gear editor at Bicycling Magazine contacted me to participate in an article on which he’s working. We talked today for a while about titanium, Seven’s place in the industry, and some of the work that Merlin Metalworks and I did many years ago. One of the interesting aspects of our conversation included titanium’s unique ride characteristics. The way in which a good rider can apply body motility very differently from any other material; a well designed titanium bike works with the rider’s body English, not against the rider, or more accurately, not without the rider. Other materials may be predictable but they are not nearly as controllable as titanium. Titanium does what a skilled athlete tells it to do. It amplifies the rider’s input. Titanium participates in the ride.
June 4, 2012: Consulting: Talked with Derek at Cornell about fatigue endurance’s relationship to bicycle frame stiffness degradation. As, I’ve mentioned before: no relationship. Some of the points we discussed included:
- Fatigue testing article from 25Seven – that’s how he found me
- Material modulus does not change in any real world bicycle use
- Bicycle frames are more often designed for impact resistance – yield and ultimate strength – rather than long-term fatigue cycling – real world usage
- Steel frames rust internally and that effect on frame stiffness – often confused with frame “softness”
- Aluminum doesn’t actually have a fatigue endurance so eventually, if you keep riding the bike, just like life, it will fail
Material Source Matters
December 5, 2012: I had a conversation with a framebuilder about Asian sourced titanium today. As with just about everything, there exists a stratification from best to worst – from excellent to mystery metal. Unfortunately, my consistent experience is that titanium – whether frames or raw material – coming out of China is on the worst end of the scale; some isn’t terrible and a lot is terrible. Taiwan isn’t much better. Sources for both are getting better; we’re seeing improvements every season. That’s why we do testing of materials every year or so. I don’t like to generalize and follow stereotypes but my experience is my experience. The irony is that the stereotype of ‘all titanium is good titanium’ is just plain wrong. The best titanium is more than three times stronger, and with a three fold improvement in fatigue endurance, over the worst titaniums we’ve tested. That can easily be the difference between a frame that fails in a year and a frame that lasts a lifetime.
October 22, 2012: I received a really disturbing email from a titanium supplier. The supplier sells titanium tubing with a few states of annealing – as is true with the only two mills in the country. Long story short, annealing is a way to improve ductility and formability. Sounds good, right? Unfortunately, as formability goes up, strength goes down. Cutting to the chase, this supplier sells fully annealed material to framebuilders – those that cannot form tubing. This fully annealed material is about 50% of the strength of cold-worked stress-relieved – CWSR- material, like what Seven Cycles uses. ’Half the strength’ is not a material I would recommend for bicycle building. I don’t fault the titanium supplier; they’re not bicycle frame designers so I don’t expect them to be making recommendations about what’s safe and not safe. They don’t sell ‘chainstays;’ they sell ’0.875 x 0.035″ tubing.’ However, many bicycle framebuilders are not engineers. Understanding material elongation properties – what 6% means relative to 15% is likely lost on most builders. Even knowing that material strength of a fully annealed tube is about half that of a CWSR tube seems to fall on deaf ears. Dangerous.
October 18, 2012: Reality check: A visitor to Seven Cycles asked me about titanium supply today. I mentioned, sort of distractedly, that lead-time for titanium – order to delivery – is about 18-months. The person didn’t think I understood the question. He didn’t think that 18-months was possible; he expected an answer along the lines of, “a few weeks.” And it’d be equally impossible to run a business that way, particularly when every frame Seven builds is custom so material planning is really challenging. But, if you want to use titanium made in the U.S. only two mills make the material. And therefore, lead-time is often a year and a half. Long-range planning it is. nearly impossible and yet Jennifer M. does it flawlessly.
August 18, 2012: Business Development: Titanium sourcing continues to get more and more difficult. I see this as a positive situation but it sure does take a disproportionate amount of time to manage now. Sources are fewer; partners are scarcer; material quality is less interesting to most people. Conversely, we’re actually pushing harder on improving material quality. A post for another day. Seven’s titanium is better than it’s ever been – and that’s saying a lot – but it’s more and more time consuming to keep the incremental improvements going.
Titanium Fatigue Testing
An article I wrote about fatigue testing bicycle frames.
November 29, 2012: We’ve been working on this at Seven, in a very quiet way. It’s starting to make some noise again. A good thing. I’m hoping to publish some results soon. I thought year-end would quiet down but we continue to be all hands on deck with keeping up with customer bike orders.
November 12, 2012: Fatigue testing of some titanium materials at Seven Cycles continues. The work is slow and sometimes tedious But the results are some of the most important work that we can do. Most results are predictable. Some are not. Working to track down some of the chemistry on a few test pieces.
August 1, 2012: Engineering: Fatigue testing stress risers. As part of our latest titanium testing I’ve added some stress riser tests. Years ago we did some testing that yielded pretty counter-intuitive results. I’m hoping we can recreate these results for this new generation of material enthusiasts. I want to get going on this but we can’t begin until the carbon testing round is complete. Soon.
Machining of Titanium
I have a page about fatigue testing titanium tubing.
October 30, 2012: Framebuilding Note: From my Facebook post for Seven Cycles: So many cutters, so little material. Here are a few of the tool-holders we use for tubeset cutoff. Nestled on one of Seven’s lathes and ready for the next job. Why so many in line? Partially because the next frame could be titanium, steel, or carbon. Each material has very different requirements for tube cutting. Titanium likes to be machined at “high feed, low speed,” while carbon prefers “high speed, high feed.” Feed your speed appropriately.
July 27, 2012: Testing: Fatigue testing titanium: We’ve added annealed 3-2.5 titanium to the testing program. The primary reason for this is that I’m concerned about the extent to which annealed material is making it’s way into bikes. Annealed 3-2.5 titanium typically has a yield strength of about 70 ksi. Only about 60% of the strength of cold worked stress relieved – CWSR – 3-3.5 ti. Annealed material is kind of like building frames from 6061 aluminum or low grade 4130 steel.
July 12, 2012: Project: Titanium Testing. I started on setting parameters for Seven Cycles’ next titanium testing. We’re looking at a number of test parameters: surface finish on the ID and OD, concentricity, and – most important – contractile strain ratio.
Historical Notes and Random Thoughts About Titanium
October 5, 2012: In a recent interview one of the questions I was asked was regarding titanium’s heyday: when was it? I don’t think I’ve ever had that question posed quite that way. If heyday is considered the peak of the sales bell-curve, then I think that’d be in the mid 1990s. Nearly 20-years ago. But, ‘heyday’ is an interesting word. I have a hard time feeling like the mid-nineties were the heyday. Maybe it’s the word ‘heyday’ that I find odd. If the heyday is, by definition, in the past, then everything is on a downward slide. I don’t feel that about titanium. More accurately stated about the mid-nineties: I think that period kind of wrecked titanium. Too many companies offering titanium bikes that were too cheap. A bad idea. It didn’t work out for the companies or the riders that bought those bikes. The heyday of mass produced cheap titanium has come and gone. The heyday of the best of what titanium can offer is still on the horizon. Get ready.