Caad 12 repaint and re-purpose - Frame support

Discuss light weight issues concerning road bikes & parts.
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Posts: 105
Joined: Wed Aug 10, 2016 6:05 pm

by Ltyarbro42

I have a caad12 frameset that I raced on for the 2016 season and somewhere in the middle I got caught up in a sprint crash and dented the chainstays.

I got a frame jig to it and everything was still inline so I continued to ride it for another 4000 miles, in fact. Knowing that frame member was in tension and NDS it didn't worry me a whole lot. It never cracked or gave me any issues. I've since replaced it with another Caad12 frame and I'd like to try my hand at some custom paintwork for fun on this old frame and potentially take the same paint scheme to my everyday frame.

I have an engineering background and have gotten crafty in motorsport applications in the past, but this isn't really my area of expertise. Aside from just filling the dent with Bondo/JB and painting over it, does anyone have any ideas for bracing the area around this dent? Realistically this will just be a backup frame and relegated to trainer use and maybe a backup bike.


Posts: 76
Joined: Sun Sep 23, 2012 1:53 pm

by numberSix

You could TIG buttons on it and pull the dents. Argon both sides. Then grind the buttons off and recheck the alignment.

Didn’t this guy do all of Spooky’s aluminum frames:
He might quote you a price.

by Weenie

Posts: 55
Joined: Sun Apr 05, 2015 10:27 pm

by patchsurfer

There is a specialised stud welder tool - can't remember the name of it off hand. Comes with a matching slide hammer that fits over the stud - your local panel beater probably has one.

That said though, I'd be more worried about increasing the elasticity of that area by over-working the metal than a ding, if it's not giving you any grief. Disclaimer - I only have experience working with steel. On old volkswagens.

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Location: Romania

by Alexandrumarian

I would avoid further bending/stressing of the area. Provided the frame has enough clearance, I would consider filling the dents with epoxy or maybe with polystyrene to save weight, then wrap the entire chainstay a few times with carbon fiber cloth. Perhaps do it on the other side too to maintain symmetry both visually and in terms of stiffness. A while ago there was a thread here with someone documenting a seatstay carbon repair, will be useful to look at.

The epoxy might not bond that well to aluminium due to the instant oxidization (maybe there are some special primers that help) but the carbon will act as a cast and stay tight on.

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by srshaw

I think I'd go the filling route instead of trying to pull the dents. Aluminium is as far as I understand not ideal for trying to knock out dents. I wonder if something could be put inside the chain stay for strength?

by Weenie

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Joined: Thu Sep 05, 2013 3:29 pm

by TheKaiser

Alexandrumarian wrote:The epoxy might not bond that well to aluminium due to the instant oxidization (maybe there are some special primers that help) but the carbon will act as a cast and stay tight on.

Not long ago here on WW there was a thread on some sort of carbon-aluminum bonding, and Damon Rinard chimed in with suggestions to deal with the instant oxidation. I wish I could remember what thread it was, as I think he mentioned a "proper" way of doing it, maybe with some sort of chemical treatment that will remove the oxidation and prevent recurrence, but I do clearly remember the "hack job" method he referenced complete with disclaimers as to results may vary. He said you can coat the stripped aluminum surface with a long cure time epoxy and then wet sand through the epoxy, which will remove the oxidation layer. Then the hope is that the thin layer of wet epoxy will be acting as a protective barrier to prevent recurrence of the oxidation. You can then cure that epoxy, and for the next step, be doing a less sensitive epoxy-epoxy bond, with reasonable assurance that that your base coat has good adhesion.

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