Tanstaafl

The seat post clamp on my sisters Cannondale Slice 5 has broken. The bike is no longer in production, and she has not found a replacement. She was able to obtain a PDF drawing of the part, but it is apparently not completely detailed. There is a note on the drawing indicating more dimensions are contained in the IGS file. We can create a new CAD model from the PDF, but I am not sure how correct we will get the airfoil section without the details available in the IGS file. Right now, I am still trying to figure out the radius callouts. My concern is applying uneven stress to the seat tube on the bicycle as the clamp is tightened. I don't want to crack the frame due to uneven loading. Is this something I should be really concerned about, or is 'close' going to be good enough? Normally, I would create a CAD file, run a 3D print of the part to check for fit, and go from there. The problem is she needs the bike in three weeks for a triathlon. so we don't have much time. I have attached a picture of the clamp and the PDF drawing.

Thanks,
Jeff

himespau 

Do you have a friend with a welder who can weld it back together for a short term fix?

jccaclimber

If this were me and I was using SolidWorks I would take a very square photo, insert it as a sketch aid, zoom in, and draw a spline to fit.

Is it a NACA profile by chance?

For a one off, traditional hand fitting may work as well.

MrMazda

I would say it depends on how "close" you can be... I thinks the forces involved here are greater than we all imagine and that the thinnest parts of the collar will stretch to a point where the collar will conform to the post.
Pretty sure if you are within .010" of the real dimension, you'd be ok.

I'd be more worried of the strength of the material used to make the part as it may very well break easier than the original did...
Given the situation you are in, I'd go ahead and try... Especially if you are able to 3D print a prototype that you can try on and look for gaps!

Tanstaafl

I know very little about welding aluminum, other than those who can do it have obviously sold their soul to learn the secrets. My concern about this is we are trying to weld a thin section (3mm nominal) of yielded material that is permanently deformed at the break.

MrMazda

I have to agree, welding it is your best and quickest option. I would file what is deformed (interferes with post) and try to find a way to hold things together at proper position (not obvious) and bring (whole bike??) it to a qualified welder who will make sure nothing moves while he welds. This is conical, both halves have to line up! Maybe use an additional nuts with a longer screw could hold both halves while resting on a flat surface...
Wondering if this could be done while on the frame?? How is carbon sensitive to heat?

Crankycrank

Houston should have some skilled aluminum welders. Try checking some motorcycle shops, off road vehicle shops, etc. for recommendations. A good welder can slightly build up the thickness of the clamp near the break and re-shape the deformed area so it fits and doesn't break again. Also, if you haven't already, contact Cannondale directly. They may have a secret stash or have some solution for you and call around to all the Cannondale shops as they may have a spare sitting around.

70sSanO

I would contact Cannondale and see if they have any suggestions. It might be that a different non-Cannondale aero clamp will work. They may or may not be helpful, but rather than trying to mfg a one off, it is worth a try.

The other option is to find an aero clamp that will be long enough and fit over the frame. You might be able to build it up, epoxy strips, on the ID and then painstakingly shape it to fit.

John

Mista Sparkle

What's your budget?

since you have the pdf with a good cross section it should be easy to extract the profile from it and put together a suitable model.

Probably $150-300 to have a single part run of the model by somebody like protolabs. Probably similar in price to a single 3d printed one.

dedhed

You have a drawing, with material specs. Buy some 6061 stock and have a machine shop fab a new one.

https://www.onlinemetals.com/en/buy/...ruded/pid/7007

pdlamb

If it were me, I would NOT copy the drawing and build another one just like it. The original already failed. So at the very least put some more bulk on the outside of the part where it broke, and just worry about matching the inside design. For that matter, I'd be looking at reproducing it in a good steel for extra strength, instead of light-but-weak aluminum.

And the next time you buy a bike, remember the problem this fancy-schmancy part caused, and buy a bike with a standard circular seatpost.

flanso 

The 2010 Cannondale Synapse Carbon that I used to own had a similarly shaped "elliptical" seat post. The clamp may be more common than one would think; try Cannondale.