Why thickness is a parameter at all
A PVD coating is a thin ceramic layer deposited on the tool's surface - hard, heat-resistant, and chemically quieter to the workpiece than bare carbide is. Its thickness is a real engineering parameter because the layer has two jobs that pull in opposite directions. Thick enough, it shields the carbide from heat and wear and lasts. Too thick for the job, it rounds the edge it covers - the coating wraps the cutting edge like paint wraps a corner - and a tool that was ground sharp arrives merely covered. So thickness is specified per application: enough to protect, not so much that it blunts. The actual value is a factory figure, confirmed on the spec sheet per program; what a buyer specifies is the family and the intent, not a guess in microns.
The trade in plain words
Think of the edge under the coating. A heavier layer adds protection but softens the edge radius; a lighter layer keeps the edge keen but offers less barrier. Roughing and abrasive work lean toward the heavier side - edge keenness matters less than shielding. Finishing and fine-feature work lean toward the lighter side - the edge geometry is the product. This is why two coated tools of identical geometry can behave differently across applications, and why "coated" alone is not a specification. The desk writes the coating line with the application next to it, and the factory confirms the resulting thickness per program in writing.
Edge preparation: the partnership that has to work
Coating does not rescue an unprepared edge; it records it. Before coating, tools go through edge preparation - a controlled honing that rounds or strengthens the cutting edge to a deliberate profile. Honed edges hold coatings well, because the layer adheres over a smooth supported form instead of bridging across grinding marks; a coating over a poorly prepped edge flakes and lifts where the foundation is rough. Too much honing dulls the tool before it ever cuts; too little leaves the coating without structure to grip. Edge prep is therefore part of the geometry package the desk specifies: a process line at the partner factory, checked at inspection, not a detail left to chance. The production sequence - grind, prep, coat, mark, inspect - is laid out on the production process page.
| Coating line | Plain meaning | Typical fit |
|---|---|---|
| TiAlN family | Heat-resistant nitride layer for hot cutting | Steels, dry machining |
| TiN | General-purpose gold nitride layer | General milling, lighter duty |
| Uncoated, polished flutes | No layer; polished surface denies grip | Aluminum and gummy non-ferrous |
| Diamond family | Hardest layer, for abrasive work | Abrasive non-ferrous, composites |
Families first, thickness second
In practice, buyers choose the coating family before they think about thickness, and that is the right order. The TiAlN family handles steels and dry machining where heat is the enemy. TiN covers general purpose at lower demand. Aluminum usually wants no coating at all - polished uncoated flutes, because most nitride layers give sticky aluminum somewhere to weld. Abrasive non-ferrous materials and composites justify the diamond family. Each family is deposited within a thickness window the coating line controls; within a family, the fine choice of where in that window to sit is the factory's engineering job, confirmed per program. The family comparisons are laid out in TiN vs TiAlN, the polished-flute case in uncoated end mills, and the deposition itself in PVD coating basics.
What coating thickness is not
Three corrections to catalog folklore. Thickness is not a grade - a thicker layer is not a better tool, only a differently balanced one, and often a blunter one. Thickness is not uniform folklore either: layers follow the tool's shape, thinning over sharp features, which is exactly why edge prep and coating have to be planned together. And thickness is not a buyer-visible number to chase: it lives on the factory's process sheet, checked at inspection, quoted per program. A buyer who specifies "TiAlN family, confirmed thickness on the spec sheet" has said everything that can honestly be said before samples run in the actual material.
How the desk handles coating questions
The desk treats coating as a program line, not an upsell. The quote names the family, the application it serves, and the confirmation that thickness and edge prep are the factory's responsibility within the program - in writing, checked at inspection, traveling with the certificate of conformance. For standard catalog items the families are already matched to the geometry. For OEM programs, coating choice is made against the customer's material and operation, sampled, and fixed before bulk. Coating adds a few days to bulk lead time, since grinding and coating run on separate lines - a reference point confirmed per program on the MOQ and lead time page.
Coating, regrinding and the second life of a tool
Coating decisions outlive the first use of the tool. A regrind removes the worn layer along with the worn edge, which leaves bare carbide behind - so a reconditioned tool that ran coated either runs uncoated, with the behavior change that implies, or goes back through the coating line before it returns to service. Most programs that started coated choose the recoat: the geometry is restored to the original grind, the edge is prepared again, and the layer is reapplied so the tool re-enters service as the same specification rather than a compromise. Regrinding and recoating are quoted per batch and confirmed per program in writing, because the cost and the cycle time move with the coating family as much as with the geometry. For buyers, the practical line on the program is the pairing: which coating the tool carries, and whether the reconditioning route includes a recoat to match. A tool specified once as a system - substrate, geometry, coating - stays that system through its regrind cycles only if the sheet says so.
What to write on the spec sheet
The coating line reads: family, application, and confirmation - "TiAlN family - steel, roughing; thickness and edge prep confirmed per program". For aluminum: "uncoated, polished flutes". If a program needs a specific thickness regime, that goes in as a requirement for the factory to confirm in writing, not as a number invented at the buying desk. Pair the line with the substrate it protects. That sentence - family, intent, confirmation - is the whole honest specification, and it is the one the desk puts in writing per program through the quote form.