I am thinking of making a Carbon Fibre Harp.
I am having a problem with how to make the neck and column.
If you don't know, this is shaped like a curly number seven. It needs to be very strong as it has about 500 Kg of pull across it from the strings. I would like to make it in one piece. The sound box fits between the ends of the seven but this is relatively easy.

I was thinking of making it in a mould made of sheets of MDF laid flat with the cavity cut out of the middle sections.

I would make the piece by wrapping layers of Carbon Fibre around sections of expanded polystyrene so that it would end up with an internal box section support structure.
I would also include a bicycle inner tube so that when the top is bolted on to the mould I could inflate this and force the piece into the corners.
I was wondering if I could laminate using infusion resin and include a length of spiral tube between layers leading out of the mould so surplus resin would be forced out. I think the laminating resin would be too thick to do this.

Does anyone think this would work?

Brian.

Hi Brian,

I understand your plan and it's an interesting one. I did not realise that you wanted internal shear layers of reinforcement, I imagined just a foam core and then the reinforcement like a 'box section' around it. Having the shear layers will add lots of strength but certainly complicates your construction so that you end up needing to make it the way you plan. If you did without these intermediate layers then you could simply make the foam core an almost perfect fit for the MDF mould and then wrap your carbon around the foam core (which would be easy to do with the core out of the mould) and laminate it through with resin before squeezing it down into the mould, putting your end cap on and inflating the inner tube.

I've got to say that I think you'll have problems removing the part from the mould if you have parallel sides and hope to lift the part out somehow by simply removing the 'top' sheet of MDF - you'll have nothing to grip on, the parallel sides will lock in the part and the none radiused corners will also lock the part. This is fair enough if you plan on dismantling the MDF mould completely to get the part out but just don't expect to be able to get it out without doing this.

I'm also worried about these none-radiused 90 degree corners. The fabric is likely to bridge around these corners leaving them looking far from perfect. Radiused corners (even if you only do it with plasticine or filleting wax) would help a lot but you can't do it unless you had a centre split line (when you could also make the sides taper slightly too!).

Good look with it - I'll be watching with interest.

Best regards, Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales