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,

Thanks for the post. You've got some interesting ideas there and some that maybe I'm not quite following.

Taking the process in order, it would be perfectly possible to make a 'one-off' mould using sheets of thick MDF and profile out your shape by cutting some of the layers to form the cavity. You could use a ball router to radius the inside corners or you could cut the sheet straight through (using a jigsaw) and then, when the bottom 'closing' sheet it in place you could use bodyfiller or something similar to radius off the inside corner. You would need to do this to avoid any awkward 90' corners. To make the MDF more sturdy and therefor cabable of taking the moulding pressures I would thinkt hat you'd need to coat the whole surface in some lightweight glass and epoxy and then flat that back. Finally, I would suggest a 2 pack high build filler primer as the surface layer which again you would flat and then polish. As you've planned, make this in two halves that bold together. Pu the the split line dead centre (rather than just making it so that you remove the top sheet to remove the part) as this will make it much easier to demould and also mean that you can put the radiuses in the top and bottom corners.

For your pressure moulding process, I don't understand exactly how the polystyrene foam is going to work along side the bike inner tube? - Do you intend having the inner tube inside the polystyrene core? If so I've not gont any experience of such a process but I can see some merit in it (specifically that it avoids the neccessity to have something like an inflatable silicone bladder) and that it gives you a good positive shape to laminate around prior to putting the laminate into the mould. If this process was to work it might be worthwhile wrapping the foam core with release film (first) then breather, then perforated release film. The release film would stop any reson from sticking to the foam core, the breather would be there to facilitate airflow out of the laminate and absorb excess resin and the perforated release film would be there to allow excess resin to flow from the laminate into the breather.

As projects go it's adventerous but exciting too and I can see that good results could be acheived if you put the work in with to make a decent mould (it's always the way!).

All the best, Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales