I would suggest to grind it flat, use an aluminium tube inset and araldite it in place.

Horrible stuff to machine. Splinters and burrs are common. I would probably araldite a piece of metal in each end, Then face back to clean up while in a collet. Face right up to the collet face. Then drill and tap both parts and glue some threaded rod to pull it all together.

Maybe glue a polished brass band over the join to hide it?

I hold the tube in a collet in the lathe and use a pointed tool at low speed to nick through far enough to get a clean break. Square off with fine abrasive paper. Araldite + ali tube or rod to reinforce will be fine. Need the metal to be a nice fit in the CF tube. My 7kg clock bob has been hanging off an 8mm aluminium slug araldited into 10mm OD 8mm IS CF tube for over 3 years with no sign of coming adrift.  Gluing in a slug also holds any longitudinal cracks together.

Edited By John Haine on 03/04/2022 09:41:02

How much strength is required? I think that any type of internally reinforced butt joint will be quite weak as the fibres are discontinuous and will not carry bending stresses. An angled splice joint might be better but difficult to make unobtrusively.

Never tried to repair Carbon Fibre so I'm short of ideas. I think it's too difficult. Carbon fibre rod is made of extremely thin carbon fibres embedded in a brittle resin matrix. Rod is very strong along the fibres, much less sideways. This picture is of the suspension of my experimental clock pendulum, where I removed a section of matrix so the pendulum only swung on the flexible fibres, independent of the resin. The example is 0.8mm diameter, but the construction is the same in bigger diameters.

Appearance depends on the matrix, which should be easy enough to recreate. Unfortunately, the strength of the rod depends on the fibres, which can't be reconnected. The best I can think of is like Clive's answer, except I'd use a steel rod rather than Aluminium tube. (Carbon fibre is stronger than steel!)

I found cutting thin rod no problem with a wire-cutter or rolling a sharp Box Knife over it, but it gets harder to do it neatly as the rod diameter increases. Radio Control types recommend rolling the rod on a wet cloth with a razor blade. The problem is the brittle matrix tends to crack and chip, causing nearby fibres to stick out in an untidy fuzz. A Dremel cutting disc might do a better job: I've not tried it!

My feeling is the item can be made to look good again, but the repair won't be strong enough to allow the baton to be waved about.

How about the dead Hamster fix? When the child's favourite pet dies, take the corpse to a pet shop secretly and replace it with a near match. If all else fails, tell the friend to substitute a new one without telling his wife!

Dave

How on earth did he snap it!

I wonder if the cleaner solution would be to get another piece of carbon fibre and replace the shaft complete? Rods are easily found, used in everything from Model RC Aircrft and and Fishing rods as metioned before.