CNC cut-to-size plywood and MDF: what to order and how
Sometimes you don't need a carved sign or intricate art. You need panels: cabinet sides, shelves, drawer boxes, a desk top, speaker baffles, a set of flat-pack furniture parts. Getting sheet goods cut to size accurately is surprisingly hard without a big shop, and a CNC router is one of the best ways to get it done. Here's what to know before you order.
Router or panel saw?
Lumberyards and big-box stores will often make straight rip and cross cuts on a panel saw. That's fine for rough breakdown, but tolerances vary and you only get straight lines.
A CNC router is worth it when you need any of these:
- Accuracy across many parts. Every part is cut from the same file, so twenty shelves come out the same size.
- Square corners you can rely on. Good for cabinet carcasses that need to go together square.
- Holes and pockets. Shelf-pin holes, hinge cups, hardware pockets, cable grommets, handholds, cut in the same setup.
- Curves and notches. Rounded corners, cut-outs for plumbing, scribes, toe kicks.
- Joinery. Dados, rabbets, slots for slot-together furniture.
If all you need is three rectangles, a panel saw may be cheaper. If you need forty parts with shelf-pin holes, the router wins.
Material choices
MDF. Flat, stable, cheap, smooth faces and edges that machine cleanly. Ideal for painted parts, jigs, templates and speaker cabinets. Heavy, doesn't like moisture, and holds screws poorly in its edges. Machining MDF makes fine dust, so makers who cut it a lot have good dust collection.
Baltic birch plywood. Many thin plies, few voids, attractive edges that can be left exposed. The go-to for routed furniture and drawer boxes. Often sold in 5×5 ft sheets and metric thicknesses (12 mm, 18 mm).
Hardwood-veneer plywood (birch, maple, oak, walnut faces). For cabinet sides and furniture where the face will be stained or clear-coated. Check the face grade and say which side shows.
Construction plywood. Cheap, but voids and rough faces make it a poor choice for visible work.
Melamine and prefinished panels. Possible on a router, but the coating chips with the wrong bit. Ask the maker before you assume.
Thickness: measure, don't trust the label
Sheet goods are often a little under their nominal thickness, and imported plywood is usually metric. If panels fit into dados or slots, the slot must match the actual sheet. The best approach is to ask the maker to measure the stock and size the joinery to it, and to write that into the brief: "dados to fit the actual sheet thickness."
Sheet sizes and the largest part
A full sheet is 48 × 96 in (4×8 ft), and metric sheets are commonly 1220 × 2440 mm. Baltic birch is often 60 × 60 in. Check the largest part against the sheet size and, separately, against the maker's machine bed. Many hobby routers are 2×2 ft or 4×4 ft; a 4×8 table is a bigger machine. Put the largest dimension in your post so only makers who can cut it will bid.
How many parts fit on each sheet decides the material cost. The sheet nesting calculator works out parts per sheet once the bit gap and edge margin are taken out, and how many sheets a run needs.
Edges
A router leaves a clean, square edge that usually needs only light sanding. A few things to decide:
- Exposed plywood edges: leave raw, sand, or edge-band (veneer tape or solid wood). Edge banding is extra labor.
- Rounded edges: a roundover bit or a chamfer bit can be run on the router as part of the job.
- Tab marks: parts are held in place with small tabs, which are cut and sanded off. On visible edges, ask for tabs to be placed on hidden edges or cleaned up carefully.
Inside corners
A router bit is round, so inside corners on cut-outs come out with a radius matching the bit (around 1/8 in for a 1/4 in bit). For notches that must fit around something square, ask for dog-bone relief cuts, or accept the radius and round the matching part.
Writing a good cut list
Most cut-to-size jobs don't need a drawing at all, just a clear list. For each part:
- Part name (e.g. "left side")
- Width × length × thickness, with units
- Quantity
- Grain direction if it matters
- Any holes, pockets or notches (attach a sketch or DXF for these)
- Which face is the show face
Add the material and grade, whether you want offcuts returned, the finish (raw, sanded, edge-banded), and pickup or delivery. Large panels are expensive and awkward to ship, so a maker within driving distance is often the best value.
Keeping the price down
- Put everything in one job. Setup is paid once, and nesting more parts together uses sheets better.
- Let rectangles be rectangles. Rounded corners and decorative curves add path length.
- Be flexible on grain for hidden parts so the maker can nest more tightly.
- Do the finishing yourself if you're comfortable sanding and edge-banding.
- Supply the sheets if you already have them, and say so.
When the list is ready, post the job and compare bids from makers with routers big enough for your parts. Posting is free, there's no buyer fee, and the payment is held until the panels arrive and you confirm delivery.