Carbon Fibre repair glue to patch a seatpost?

Discuss light weight issues concerning road bikes & parts.
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Joined: Tue Mar 13, 2012 7:27 pm

by thumper88

It can be fixed, but even if you have the skill set the effort -- unless you are totally impoverished -- far outweighs the option of buying a new one or putting out a feeler for a used one from someone with a trashed frame...
Practical people can stop reading at this point.

OK, the whack jobs still with me?
Just for fun (though they'd all be huge wastes of time and money) there are three basic approaches to fixing this:

1. A repair on the exterior surface would take aerospace repair skills and equipment, featuring things like a nice 50-to-1 taper, grinding and sanding a perfectly tapering pit, then laying in a convex carbon fiber patch with huge overlaps that's still flush due to the taper... and vacuum bagging it for a serviceable secondary bond.
Totally unfeasible. Aerospace carbon guys prob charge a few thousand bucks for it at least.

2. Easier but potentially elegant enough to live with permanently would be an insert made in the same shape but small enough to slip inside. you would have to be able to abrade a non-glossy surface on the inside of your post and scuff sand the outside of the carbon insert... which you'd want a bit thinking wall than the original.

There are various ways to make it, like taking a female fiberglass mold off the outside the post, filling it with instant foam, remove it, and use a tool to score it to a depth a bit more than twice the skin thickness of original part, then plane it until the full depth of the score is removed and use that for a core/female mold.
Then build carbon around it, given that so much structure remains in the old piece, you could laminate almost entirely unidirectional to it vertically with maybe one layer of thin 90 degree weave set at 45 degrees to finish... wrap in packing tape and cure, then remove tape... scuff it and glue it inside the old seat post.

3. The cheap, jiffy version: someone says, look, I need this thing fixed up enough to ride in 24 hours for my A race and cervelo can't overnight one. Get a bunch of epoxy (West system from a marine store is best, especially with the slow hardener which will eliminate risk of hot cure). Get a bunch of something with a vertical shape that is strong enough. AN alloy pipe, or a bunch carbon arrow shafts, or a bunch of hardwood dowels of different sizes so that they fill as much of the volume as possible, whatever. Filling up a lot of the volume will reduce the chance the epoxy will overheat. In hefty volumes as it cures it can heat up so much it would destroy the structure of the post... tape off the crunched area with clear packing tape so nothing can ooze out and change the shape of the post.
Pour enough mixed epoxy inside that it -- along with the dowels or whatever -- will fill the entire inside. shove the dowels in all the way, with enough length that they protrude from the bottom. When it cures, cut them off.
Ride the race, remove the post and throw it away and call cervelo and order a new one. Voila.

by Weenie

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