The circular parts need to be 6-8mm thick and i'm wondering if the following method is feasable for their construction. Using rectangular pieces of twill, arranged in a circle and built up to the required thickness which can then be cnc cut to shape (in yellow). I've never done compositing before so i'm wondering roughly how much twill would be needed to build up the thickness to what i need and will this method produce very rigid parts, bearing in mind that maintaining optical alignment is critical as the scope is purely for astrophotography. Thanks for any advice.

If that were my project, I'd CNC a quick circular mould, cut the core to shape, wrap the core in tow in both directions i.e. alternating between around the core like a transformer and circumferential/concentric rings then press into the mould with a matching top/flat sheet and whack under a vacuum & apply heat.