I have been experimenting with various materials to find an appropriate oscillating "mast" to support a striker in a wind driven musical sculpture. 6mm carbon fibre tube looked very promising except that it displayed a distinct bias in its patern of deflection. I assumed that this was a result of the process of it's manufacture and purchased some carbon fibre rod expecting this to behave in a uniform manner. Disappointingly the rods (especially in small section) display at least as much bias as if they are made up of ribon layers rather than strand. Any suggestions?

Without some kind of idea what you mean precisely by your "bias" or scale of deflection it is hard to advise what is best.

If it is our products you are talking about, then both our Pultruded Carbon Fibre Tube 6mm and our Carbon Fibre Rod are manufactured by a process of pultrusion and hence both products are made up of uni-directional fibres running along thier length.

In that sense I would expect very similar type of behaviour, although the magnitude might vary dependant on diameter and actual numbers of fibres.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thanks for the very prompt reply. I attach a sketch which I hope explains what I'm trying to achieve and what I'm getting right now. By bias I mean that if you take a lenth of cf rod say 2mtrs long and let one end rest on the floor at an angle with the other held in your right hand and you bend the rod at it's centre with you left hand whilst rotating with your right there are two very distinct zones of resistance to deflection at 180 degrees to one another i.e. in the same cross sectional plane. I don't know how the fibres are laid up in the pultrusion but they seem to behave as if they are layered (ribon) rather than random (strand). I suppose the real question is am I looking for something that cf rod does not have? 

I guess it is possible that some stresses are set up in the rod from manufacture.

There could also be some very slight movement of the fibres while it was pultruded.

Other than that I would agree that the rod should be able to deflect in all directions more or less.  Maybe it is too stiff and as such flexes only in the direction of its natural weak point.  A thinner rod may flex more randomly.

Other than that I can only suggest perhaps another material.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant