Ok, 20 mm CFRP bar - need the tip to be ground down to 4 mm (flat), for a 50 mm section, what's the best way to do this?

Well, we don't sell a 20mm carbon fibre bar so I don't know what type of bar this is or how it's made (I'll assume it's a pultrusion). Machining a pultrusion like this would need to be done with great care because pultrusions are liable to splinter when they're worked like this. I think I would put a rotary cutter  (like our 32mm Perma-Grit Rotary Disc) in a pillar drill and then hold the bar in a vice at the right height and then slide it along to make the cut. Before you do this I would make the vertical cut at 50mm to the right depth so that as you cut through horizontaly you can meet up with the vertical cut to get a neat edge there.

I hope this helps.

--Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales