Frame safety

I use established materials and methods to fabricate a safe, reliable, tough Métier Vélo frame.

For every new frame model,  big name bicycle manufactures build a number of prototypes and test them to destruction to see where they fail.  But for a small builder doing full custom, every frame is a prototype. Without extensive prototyping and destructive testing, how do you know a frame from a custom builder is safe?

I address safety in five ways:

1. Use established materials and methods
2. Build conservatively
3. Select clients carefully
4. Offer no-questions, free repair & replacement
5. Keep liability insurance current

Having made these points, fellow builders at NAHBS 2016 offered to test a frame to failure for me at minimal cost. It is very generous of them.  Most likely, the NAHBS Winter Training Bike will be sacrificed sometime this summer.  After I do a post-mortem, I'll send the lugs back to GPI for evaluation.  I’ll post the results here.

In the meantime, read on for more detail.

1. Use established materials and methods. Métier Vélo frames are made with stock carbon tubes from Rockwest bonded into 3D-printed 6/4 titanium lugs from GPI Prototypes using West System toughened epoxies. Métier Vélo frames have a traditional layout and appearance reminiscent of lugged steel frames.

• Bonded carbon-titanium: Several framebuilders make titanium carbon bonded frames (Seven, Firefly, Bruce Gordon, and Bastion are ones I can think of off the top of my head), and bonded titanium-carbon parts are common in the aerospace industry, even for mission-critical components.  Carbon and titanium are compatible galvanically, and have similar coefficients of thermal expansion so the mechanical bond should not fatigue appreciably. 
• West System epoxies: I have extensive experience using West System, and consulted with Gougeon Brothers (manufacture of WS) about building bicycles. To my knowledge, Boo Bicycles uses the 105/209 system and has  not experienced bond failures. West System 105 resin system is appropriate to bond carbon & Ti, and I used this system on two frames, one of which has at least 1,200 miles on it. After consulting further with Gougeon, I switched to building with G/flex epoxy.  It has a lower overall strength but a better failure mode.  G/flex is somewhat elastic and will stretch before failing. 
• Rock West carbon tubes: I use stock bicycle tubing from RockWest Composites.  The layup and intended purpose of the tubes is bicycle framebuilding. Several other builders are using their tubes, and RockWest has established itself as a legitimate supplier of high quality carbon tubes.
• 3D-printed 6/4 titanium lugs by GPI Prototypes: GPI prints end-use 6/4 titanium parts for the aerospace and medical implant industries. GPI’s 3D-printed titanium parts function under extreme conditions in aerospace applications, and bonded titanium-carbon parts have along service life.  By definition, medical implants need to last a lifetime.
• Traditional lug shapes and layout:  Métier Vélo lugs have a traditional shape and appearance reminiscent of lugged steel frames, so their general design should reproduce the proven function of traditional lugs.  
• Minimal finishing and no paint: I leave Métier Vélo frames bare with nothing hiding the carbon, titanium or bonds, so any problems that might occur should be visible.

Proper preparation and attention to detail ensure a strong, safe bond.

2. Build conservatively. I stay well within the limits of my materials and methods, and leave a margin for error.

• Titanium prints: the recommended minimal wall thickness of 3D-printed titanium is ~0.4 to 0.5mm. The wall thicknesses of Métier Vélo lugs varies between 0.75mm at the ends of the lugs to  1.5mm in areas that should have more stress (downtube-bearing race junction, for example).
• Bond surface area: The lug-tube interfaces are 3 to 4 times what a bicycle should need, and are based on bonded frames by other builders and on rough calculations from data about carbon-metal bonds. 
• Bond line: I control the bondline to ensure the optimal amount of epoxy remains in the bond regions. I either use 0.2mm microspheres in the epoxy, or print bondline control structures directly in the lugs. 
• Tubes: RockWest stock bicycle tubes have a wall thickness of ~1.3mm and have 10-12 layers of carbon in the layup. They are nowhere near the limit of what I've experienced on high end manufactured bicycles.  I can squeeze the top tube of a Cervelo RCA between 2 fingers and feel it give way—don't sit on the top tube.
• Respectable, but not super-light: Because I use more titanium and carbon than is minimally necessary, my frames probably won't ever be much below 1,000 grams or so.  My goal is to make tough, durable, repairable frames that perform well.  If you want a 550g climbing frame, I am not your builder.

3. Select clients carefully.  I accept orders from the general public, but I will only select clients who know their way around a bicycle and will spot problems.  There has been a lot of interest in Métier Vélo frames from people with engineering and composites backgrounds.  Clients attracted to Métier Vélo tend to possess the requisite knowledge.

4. No questions repair and replacement. If there is any question about a Métier Vélo frame, I want it back.  Race crash, car crash, garage with the roof rack.  Doesn't matter.  A day of my time and a few hundred dollars worth of carbon will fix the problem and eliminate the risk of anyone riding a damaged frame.  Even if I have to replace an entire bicycle and eat the cost, the business can withstand that and I will sleep well at night.  When I consider the alternative, if I thought one of my frames injured or killed someone I could not live with myself, and the business would not (and should not) survive. ​

5. Current liability insurance. If the unthinkable were to happen, and you were injured on a Métier Vélo  frame, my liability insurance will cover your expenses. Insurance is just the responsible thing to do.