When we talk about mold base structure, the first decision is almost always two-plate versus three-plate, and that choice ripples through everything downstream—parting line, gating, ejection, and maintenance access. A standard two-plate base (A/B plate with a single parting surface) handles the majority of simple, single-cavity or multi-cavity tools and keeps the stack height low, which matters when you are squeezing a tool into a small tonnage press. The three-plate base adds a stripper plate so the runner can drop independently of the part, and that is where you start paying for it: taller stack, more guide pins, and a more complex opening sequence that has to be timed correctly or you will drag the runner. In our shop, the rule of thumb is that if the gate has to be centered on a multi-cavity layout and you cannot justify a hot runner, the three-plate earns its keep; otherwise, stay two-plate and save the headaches.
Once you move into hot runner systems, the base design shifts from "how do I pull the runner" to "how do I manage heat and thermal expansion." A hot half needs insulation plates, a manifold pocket with proper clearance, and wire routing that does not pinch or chafe—details that are easy to draw and miserable to fix after the base is machined. We typically spec a manifold pocket depth with 0.05–0.10 mm clearance per side to allow for thermal growth, and we never skimp on the support pillars under the manifold plate; a sagging plate will leak at the nozzles within a few thousand shots. The 24 typical structures in common use are really a menu of these trade-offs: stripper-plate ejection for deep-draw parts, slide cores for undercuts, and floating cavities for thin-wall precision work. Picking the right one is less about theory and more about matching the base to the press, the resin, and the maintenance access you actually have.
What separates a good base design from a great one is the boring stuff: guide pin and bushing fit, return spring preload, and whether the ejector plate has enough travel clearance before it bottoms out. We have seen more tools fail from a mis-sized ejector plate than from a fancy gate. Keep your standard base library tight, document the opening sequence, and verify stack height against the press platen before you cut steel. If you are sourcing bases or comparing standard structures for a new project, it helps to have a reference library on hand—you can browse mold base and component sourcing information at MoldSo (www.moldso.com) to cross-check options before committing to a design.