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Subtitle: Save the customer money and cut quotation and communication back-and-forth at the same time
What magnet-customization factories fear most is not a complex drawing — it's a drawing that "looks professional but is either impossible to make or very expensive to make." Many R&D engineers new to magnetic design bring the intuition of machining or plastic parts to magnets, and the result is either no quotable price, repeated sample revisions, or production costs far above expectation.
This article lists the 5 most common, and most "costly and communication-heavy," design mistakes. FAIZEAL has seen each of them dozens of times. Avoid them, and the customer saves real money while the factory saves quotation and engineering round-trips.
The mistake: The drawing calls for "radial 16-pole magnetization" on a part only Ø6 mm in outer diameter; or requires a 2 mm-thick micro ring to be simultaneously axially and radially magnetized; or wants a Halbach sinusoidal array on a magnet the size of a fingernail.
The cost: When the part is tiny, the pole pitch shrinks below ~1 mm and conventional magnetization tooling simply can't grip it; a combined direction needs two tooling steps and two magnetization passes; a complex pattern (Halbach, skewed, radial multi-pole) needs sufficient diameter and space. When such a drawing reaches the factory, there are only two outcomes — no quotable price, or a sky-high tooling fee — followed by a long redesign cycle for both sides.
The right way: The magnetization pattern and pole count must match the part size and process limits. For small parts, accept fewer poles and a simple direction; reserve complex patterns (Halbach, skew, radial multi-pole) for parts with enough diameter and margin. The most critical point: do a magnetization-feasibility check with the magnet factory before finalizing the drawing — a few minutes can avoid weeks of rework.
Why it saves money and communication: Confirming "can it be magnetized, and how" up front lets the quote come the same day and the sample be right the first time, eliminating both the remolding and redesign costs.
The mistake: Total length, an appearance face, or a non-mating step is called out at ±0.01 mm; or Ra 0.2 μm roughness is demanded on a surface that is never seen and never contacts anything; or concentricity of 0.005 mm is required when the actual function only needs 0.02 mm.
The cost: Every tightening of tolerance isn't a linear cost increase — it jumps. Going from ±0.05 to ±0.01 may add a grinding pass, shift from sampling to 100% CMM inspection, and raise scrap rate; combined cost can double or more, with longer lead time. And these tight tolerances contribute nothing to the magnet's actual performance.
The right way: Drive tolerances from the functional requirement, not from "tighter feels better." Tighten only what affects air gap, assembly fit, or magnetic-circuit symmetry; relax everything that doesn't touch, doesn't mate, and isn't in the flux path to economical tolerances. One sentence: spend tight tolerance only where the knife edge is.
Why it saves money and communication: Rational tolerances mean the factory doesn't add equipment and full inspection for a few microns of "face"; the quote drops directly, and the drawing doesn't bounce back with "can this be relaxed?"
The mistake: Believing "higher energy product is always better" and picking N52 without thought; or the reverse — specifying SH, UH, EH high-temperature grades for a room-temperature part just to feel safe.
The cost: N52 costs noticeably more than a standard grade like N42, and the more "maxed-out" the energy product, the weaker the coercivity and temperature stability tend to be, and the harder consistency becomes — paying more while buying lower reliability. High-temperature grades (SH/UH/EH) are the same logic: a room-temp part using them means permanently paying for temperature capability it never uses. The opposite mismatch is worse: forcing a room-temperature grade into a motor above 120°C causes high-temp demagnetization and whole-unit rework — a far bigger cost.
The right way: Select grade by working temperature plus coercivity safety margin, not by the magnitude of the number. Room temperature with no high-temp risk: N/M grade suffices; above 120°C consider SH/UH; for ultra-high coercivity while saving cost, the heavy-rare-earth-free high-Hcj route is an option. Let the magnet factory help select by duty — more accurate than guessing.
Why it saves money and communication: The correct grade immediately lowers raw-material cost; duty matching also avoids the "sample made, tested, demagnetized" second development round.
The mistake: An indoor-dry part specified with "Ni-Cu-Ni + epoxy + Parylene, all three layers"; or the reverse — a marine or chemical-environment part given only a thin nickel layer or no treatment at all.
The cost: Three stacked coatings can eat 50–100 μm of thickness, directly squeezing an already-narrow air gap, and may peel from inter-layer stress; paying for corrosion protection that doesn't exist is pure waste. Wrong direction is fatal: epoxy's ceiling is about 120–150°C; used at 180°C it softens and peels; zinc or plain nickel in marine or acid-alkali environments rusts through in months and scraps the unit.
The right way: Let the coating follow the duty. Indoor dry: Ni-Cu-Ni 20–25 μm is enough (about 500 h neutral salt spray, no red rust). Outdoor, marine, chemical: thicken or switch, evaluate Dacromet or electrophoretic coating when needed. High temperature (>150°C): epoxy won't hold — use Ni-Cu-Ni or a dry-film type. Tell the magnet factory the duty and let the coating be customized, not layered blindly.
Why it saves money and communication: No redundant coating layers, cost drops directly; correct medium matching also closes the "finished, then rusted" after-sales hole.
The mistake: The engineer's instinct is "more flux, add material" — instead of optimizing air gap and magnetic circuit, just make the magnet thicker and bigger; or the assembly drawing calls for "0.05 mm interference fit between magnet and steel sleeve," pressing the brittle magnet in like a metal shaft.
The cost: NdFeB saturates steel at roughly 1.6–2.0 T; make the magnet any bigger and the excess flux can't enter the steel — pure waste of the most expensive raw material. Worse is assembly: NdFeB flexural strength is only about 250 MPa; interference press-fit concentrates radial stress at the edge, easily chipping or even cracking the whole piece — samples shatter on press, production yield collapses.
The right way: First optimize air gap and geometry to raise flux efficiency, then decide magnet size; size the magnet to the actual flux need, not "bigger is safer." In assembly, let brittle magnets use bonding plus minimal interference (≤0.01–0.02 mm) or no interference at all, making the steel member — not the magnet — carry the assembly stress. When possible, design the magnet to be the enclosed, protected party.
Why it saves money and communication: No oversized magnet, raw-material cost drops; no cracked assembly, both yield and lead time hold, and the "sample shattered, redo" loop is avoided.
These five mistakes are essentially the inertia of "designing a magnet like an ordinary material." Magnets are brittle, magnetic circuits are demanding, and magnetization has process boundaries — none of which show on the drawing, but all of which speak through cost and data.
FAIZEAL's advice has always been simple: before the drawing is finalized, align these five things with the magnet factory once — magnetization direction, tolerances, grade, plating, and assembly method. One upfront conversation often eliminates every quotation black hole and rework cost that follows.
For magnetic-assembly design feasibility review, or grade and plating selection advice, please feel free to reach out — FAIZEAL can provide technical support.
