Building a Composite Panel with a Window Recess?

I can’t figure out how to practically build a fiberglass composite panel with a recess for a window.

The panel is 1” thick, 6lb density foam core with 36oz glass on each face.

The window design would be the kind were you subtract the thickness of the window and adhesive from the panel at the mating surface to create a flush window on one surface when the installation is complete. A modern, frameless, flush window.

The question is, how the heck do I create this little rebate for the lip the window rests in from fiberglass and foam??

if I use a router after building it, there is no glass on the lip. If I create the exact shape out of foam, then try to carefully glass the lip while building the panel, it’ll be impossible to get the glass to sit down in the 90 degree angle of the lip.

How is this done?

 

Before the panel is layed up.
Create a "window" blank slightly larger than the final window will be. Bevel it's edges. Incert it into the mould and layup over it. After demolding use thickened resin or fairing compound to adjust opening to final shape.

 

Ok. Thanks! And if I already have prebuilt panels in some cases, is there an accepted method there to cut a hole and add a similar window type?

Some spots are already built.

 

Router the opening slightly large to allow for a bevel, the new FG skin, and expansion gap. Also grind away a bit of the skin so that the new skin can feather into the old without a lump.

 

2nd that. In Oz we have mdf board with a shiny laminex on each side, commonly used in kitchen cabinets. This works great as a flat mold surface with a little release wax or hairspray.