Thats why you bolt it together and grind it out with a dremel, the manifold will work as a router guide. With a small bit the manifold will stop and guide the cutting bit. I use wood carving rotory bits and a die grinder, works good on exhaust gasket and for grinding aluminum. DRILLPRO 6PCS 1/4'' 6mm Rotary Burr Set, Shank Engraving Bit Cutter, Burr Wood Carving Rotary Tools - Milling Cutter Hss Carbide Cutter Rotary File Set https://www.amazon.com/dp/B01FW4XILG/ref=cm_sw_r_cp_api_.NiUzb7A12P2C
