Eliminating "Magnet Bulge":
Engineering Invisible Closures for 4x3x1.25" Luxury Boxes

The Visual Flaw of Low-Cost Factories

Nothing breaks the "Industrial Luxury" aesthetic faster than a visible circular bump on the lid of a rigid box. This phenomenon, known as **"Magnet Bulge,"** occurs when the magnet is glued directly onto the board surface before the paper wrap is applied.

For a compact **4x3x1.25" (10.2x7.6x3.2 cm)** jewelry box, where the surface area is limited, these bulges become the focal point of the unboxing experience, signaling a lack of precision engineering.

The Engineering Solution: CNC Counter-Sinking

At **Saide Packaging**, we utilize automated CNC grooving machines to create a recessed pocket in the greyboard that is exactly **0.1mm deeper** than the thickness of the N35 magnet.

The "Glue-Trap" Calibration Formula

If the counter-sink pocket is too deep, the magnet will rattle. If it is too shallow, the bulge persists. We calibrate the depth ($D$) based on the magnet thickness ($T_m$) and the adhesive layer ($T_a$):

For our **4x3x1.25"** boxes using 1200gsm board and 10mm magnets, we target a precision depth of **1.65mm**. This allows the magnet to sit perfectly flush with the board's "shoulder," ensuring that when the 120g wrap is applied, the surface tension is uniform across the entire lid.