Carbon Fiber Tube end strengthning

[alansimpson]

I intend to use small diameter 4 mm carbon fiber tube in a product with a cut end exposed. The end if the tubes have a tendency to fray or split. Is there any liquid resin or preparation that could be applied to end of tube to reduce the tendency to split? I need to keep tube end open an ID and OD as close to original as possible.

I don't know exact composition of tube, epoxy I assume. I got it from hobby and model suppliers. Fibers arranged axially rather than wound in helical pattern.

 

[btrueblood]

A couple of ideas:

1. epoxy coating the end should work
2. try some poly shrink tube either by itself, or shrunk over wet epoxy
3. tent poles made from carbon fiber tubes/rods have aluminum end caps/fittings, presumably also bonded to the tube with epoxy.

 

[Compositepro]

What you have is a pultruded tube which may also be polyester resin rather than epoxy. Adhesion of polyester to carbon is usually not very good so fibers peel out very easily, but that will happen with epoxy as well. This is what you need to do:

1. Use a high-speed abrasive cut-off blade.

2. Support both sides of the cut so the pieces cannot move during cutting. Peeling-out the last fibers to be cut is very common if you don't do this.

3. Avoid generating too much heat during the cut. This depends a lot on the resin's heat resistance. If the resin softens and degrades at low temperature it will be difficult to get a neat cut. Water cooling may be required but be aware that wet carbon dust on metal is very corrosive to the metal (galvanic corrosion).

4. Rotate the tube while cutting very lightly into the surface. This minimizes the temperature reached at the cut. It also directs the cuting forces tangetial to the surface. With a straight through cutting action there will be times when the cutting forces are directed out from the surface and this causes peeling.

How do you do what I describe? Put an abrasive blade in a table saw, use the fence to control your cut length, and use
a piece of wood on your slide to push the tube until it touches the blade. Then rotate the tube as you slowly push it into the blade. The blade only needs to advance through the wall thickness but you can push it further to polish the cut on the side of the blade (you will cut into the wood too, but only on the first cut). Remember to hold onto the tube on both sides of the cut.

Or you can get an arrow shaft saw for a few hundred bucks which does the same thing.

 

[ScottyUK]

Possible option: tile saws have become quite common and cheap in the UK during recent years. You get a water cooled diamond blade of fair quality for not a great outlay. Might be worth a trip to your DIY store for a look. This is one of the first Google hits I got:

http://www.twenga.co.uk/dir-Garden-DIY,Portable-electrical-tools,Tile-saw

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