Investment Casting Design Guidelines: Wall Thickness, Holes, Radii & Tooling Investment casting design guidelines help engineers review wall thickness, holes, radii, flat surfaces, machining allowance, and wax pattern tooling before production begins. This article explains how part geometry affects castability, tooling cost, dimensional stability, and post-casting machining. It also shows when features should be cast directly, machined after casting, or reviewed with ceramic cores or 3D printed patterns for better manufacturing results.