A further consideration is cutting a slot just as narrow as the endmill results in near constant 100% tooling engagement — best to add geometry offset around the part and cut as a pocket down to tab depth or the penultimate pass — where possible avoid slotting and add geometry and cut as a pocket (Making vacuum hose adapters and/or Adding geometry to cut as a pocket with a finishing pass ) and consider leaving a roughing clearance and taking a finishing pass.