It is surprisingly easy to sand the middle of a box panel three times and barely touch one corner. On bare wood that is already reasonably flat, a faint pencil grid gives you a simple coverage check. The disappearing lines help you see where you have worked instead of relying on how long you have been sanding.
Start with clean, unfinished wood and an ordinary graphite pencil. Draw a few widely spaced diagonal lines across the face with almost no pressure. Test on an offcut first, especially with pale or open-grained wood: heavy marks can settle into the grain, and pressing hard can leave grooves. Skip the trick on a finished surface you are trying to preserve.
Secure the panel on a clean, stable bench. Wrap suitable abrasive around a flat sanding block and work in overlapping passes along the grain, keeping the block flat. Use light, even pressure rather than leaning on a stubborn patch. Control the dust and use eye protection and suitable respiratory protection for the wood and work involved.
Pause, remove the loose dust and look at the remaining marks. A patch of pencil may simply be an area you missed, but it can also sit in a low spot that the block is bridging. Do not dig into that patch with a fingertip or keep thinning the whole panel just to erase it. Check the surface with a straightedge before deciding whether more sanding is sensible.
Disappearing pencil lines show coverage, not a finished surface. Look across the wood in low, angled light for scratches left by the previous abrasive, and inspect the edges for unwanted rounding. Be especially cautious with veneer: a pencil grid does not tell you how much material remains, so avoid aggressive sanding and follow the panel supplier’s guidance.
Practical takeaway: try a faint grid on one bare-wood offcut before using it on a box part. Sand with a flat block, inspect what remains and stop to investigate uneven spots. Let the pencil remind you where to look, not dictate how much wood to remove.
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