Hi,

I would like to make a part with a cored cross-member that runs the full width of the part, and joins against side walls at the ends. Hopefully my sketch below shows the idea.

Materials are carbon and epoxy and I plan to use infusion. I have 2 concerns;
1) Will I get read through on the visible underside at the cored / not cored boundary ?
2) Will I get poor consolidation at side walls where the core area joins, because there is no vac bag pressure there to push the fibre against the mould ?  Is there anything I can do here to minimise this apart from ensuring the foam is a tight fit ?

Plan B is to infuse without the core, then afterwards abrade the area and wet-lay the core and top core plies onto the pre-infused part .. but i'd like to avoid this if possible.

All ideas welcome

1. Depends how thick your skin is, but generally yes you will. If you have 2+mm of solid laminate as the outer skin then you may not notice much print, but thinner than that and yes it will print. Chamfering the core would help, but not eliminate the issue. 

2. Depends how tight you make it fit. If you can't get vacuum consolidation in there, you can achieve the same consolidation by working out the compacted thickness of the sidewalls and making the core long enough that it applies that same pressure when bagged in place. Obviously this has a bit of a window for error, so I would practice this first before trying it on something critical.