CNC Routing ACX Fir Plywood

What the grade letters mean

In ACX, “A” is the face — sanded and patched, ready for paint — “C” is the back, which can show knots and splits, and “X” stands for exterior glue. The glue tolerates moisture during a build, but the wood itself still needs paint or sealing to live outdoors.

ACX is built from fewer, thicker plies than Baltic birch, which keeps it light and inexpensive but leaves room for gaps in the core, and its fir face carries a bold, wandering grain that can show through paint. Those traits decide where it belongs: structure, decking and parts that get painted, rather than show edges and fine joinery.

Where ACX makes sense

Platform decking, scenic structure, blocking, crate parts, shipping bases, templates and paint-grade flats seen from one side. The rule of thumb from the exhibit and scenic material guide: if a piece tours or its edge shows, use Baltic birch; if it’s painted, single-show and budget-driven, use ACX.

ACX is also the usual stock for crates and shipping bases that leave town with a show: it’s strong for the money, and nobody minds a C-grade back on the inside of a crate. It suits the hidden frame inside a large carved foam piece, too — CNC foam carving is quoted on request.

Thickness follows the load. Platform tops, stair treads and crate bases take the thick sheets; flats, backing panels and blocking step down; layout templates, spacers and shims use the thinnest stock in the picker. Whoever engineers a platform sets its thickness and framing, and the quote prices whichever thickness you pick, so compare a couple before you commit.

Draw the screw pattern for a crate panel or a platform top as drilled holes: the holes land where the framing does, so each panel lines up with its frame and assembly goes faster on site or in the shop.

Routing ACX: edges, voids and fits

Softwood veneers and a core that can hide voids make ACX edges rougher than hardwood plywood, so expect a pass of filler and sanding wherever an edge will be painted. Thickness and flatness vary more than in Baltic birch or hardwood plywood: plan on looser fits and give tab-and-slot joints extra clearance. The CNC routing page covers dog-bones and the other routed-joint rules.

A void can open up where a hole, slot or pocket breaks into it, so keep screws and hardware back from edges and don’t hang a load on a narrow bridge of ACX. Pockets cut into the core plies, leaving a rough floor that’s fine for a hidden recess and poor as a show face. For a template that a bearing or a flush-trim bit will follow, MDF or HDPE gives an edge with no voids.

Engraved lines — part numbers, assembly marks, a centerline for a hinge or a caster — are priced by length and usually cost less than a pocket, and they read clearly on the sanded face. Round holes down to 3 mm (0.118″) are drilled, so bolt and caster holes are made along with the part, and inside corners keep the 1/8″ bit’s 1/16″ radius.

ACX has a strong face grain. Parts turn any way on the sheet by default, so set ↔ or ↕ on a part in the quote when direction matters — long rails that need stiffness, or faces that will be stained rather than painted — and check each part’s grain arrow on the Parts step.

Painting ACX for Las Vegas sun and storms

Fir faces check: as the face veneer dries, fine splits open along the grain, and the desert’s dry air and strong sun speed that up. Prime ACX soon after it’s cut, fill and sand the edges, and paint both faces — a panel painted on one side takes on and loses moisture unevenly and can cup. Water-based primer raises fir’s grain, so sand lightly after the first coat.

Exterior glue keeps the plies together outdoors, but it doesn’t stop the wood from weathering. A painted ACX platform or set piece can serve outside for an event or a season if every face and edge stays painted; for a painted face that has to look good for years in the sun, choose MDO plywood, whose paper overlay stops the checking. Keep cut edges off wet ground and out of sprinkler spray, and touch up the edges after monsoon storms.

What an ACX order includes

ACX parts ship as cut, with the sanded face and C-grade back the sheet came with and any holes, pockets and engraved marks you drew. Filling, sanding, priming, paint, framing and assembly happen after pickup or delivery. Platforms and stairs that people stand on should be engineered and checked by whoever builds them; the quote prices the parts as drawn. For a scenic build, crate or platform made start to finish, send a custom fabrication inquiry.