Ano
Hard coat anodizing, called out on drawings as MIL-A-8625 Type III, grows a dense, thick oxide layer on machined aluminum so the surface can handle wear that would chew through an ordinary finish. If you are a buyer or an engineer about to send parts out for it, the job goes smoothly when the print answers four questions before anything ships: sealed or non-sealed, how much coating the dimensions allow for, which features stay bare, and what color. This guide walks through each one the way AnoPRO, LLC reads a hard coat print in Paoli, Indiana, and what to put in the request for quote so the cost comes back fast.
What hard coat anodizing actually changes on the part
Type III is the same family of oxide that Type II produces, grown at a lower bath temperature and a higher current density. That combination packs the structure much tighter and builds it much thicker, which is why hard coat is the finish for sliding surfaces, tooling, fixtures, actuators, pistons, guides and anything a drawing marks for wear. It is not a layer sitting on top of the metal. Roughly half of the coating grows outward from the original surface and the other half is converted from the aluminum that was already there. That single fact drives most of what follows, because a finish that adds dimension has to be planned for on the drawing rather than discovered at inspection.
The seal decision, and why the print should make it
The coating comes out of the tank porous. Sealing closes those pores, and the trade is straightforward. A non-sealed hard coat keeps the hardest, most abrasion resistant surface the process can produce. A sealed hard coat gives up a little of that hardness and gets meaningfully better corrosion resistance in return.
When the drawing states the seal condition, the shop runs exactly what it says. When it is silent, AnoPRO flags it before running and asks what the part does and where it lives. One sentence in the request for quote, such as "slides against a bronze bushing, indoor" or "exposed to weather, no wear," is usually enough to settle it on the quote instead of in an email chain afterward.
Coating build: plan for the whole thickness, not half
Per surface, the part grows by roughly half the coating thickness. Across a dimension it grows by about the full thickness, because the coating builds on both sides. A shaft gets larger in diameter by about the coating thickness, a bore closes by about the same amount, and a plate gets thicker by about the full amount. On a standard hard coat around 0.002 inch nominal, that is enough to matter on nearly every fit and thread. Heavier hard coats in the 0.003 to 0.004 inch range need to be designed for from the start.
The cleanest way to handle it is to dimension the part after finishing and say so on the drawing. A note such as "dimensions apply after anodize" tells the machinist to undercut and tells the finisher what the target is, so everyone works to the same number. The other approach, dimensioning before finishing and stating the coating thickness, works too but pushes the arithmetic onto whoever reads the drawing next. The thickness and tolerances guide has the full table by type and class.
Threads, bores and the features that should stay bare
Threads cause more hard coat trouble than anything else, because the coating builds on both flanks at once and changes the effective pitch diameter by more than people expect. A tapped hole that gauged before finishing can refuse the same gauge afterward. There are three honest options: mask the threads so they stay bare, machine them oversize by the expected build, or chase them after finishing where that is acceptable. On a hard coat part, masking is the most common answer.
The same goes for precision bores, sealing faces for gaskets and O-rings, and electrical contact surfaces. Circle them on a marked-up PDF and send it with the request. Masking and plugging carry an additional charge that is quoted with the job, because a part with four plugged bores is a different job from a part with one masked face. The masking, plugging and assembly page covers what the shop protects every week.
Clear, black or another color
Clear and black are the usual hard coat callouts, and many buyers assume those are the only choices. They are not. Under MIL-A-8625, Class 1 is non-dyed and Class 2 is dyed, and the class rides on either type, so a black hard coat part is a Type III Class 2 coating. Our MIL-A-8625 callout guide reads a full callout element by element. Hard coat takes dye and AnoPRO runs other colors on request. The dense coating is naturally darker than Type II, so a given dye reads deeper on it. If color matters, send a color target with the print and the shop will confirm what is achievable on your alloy before quoting.
When the part also has to be slippery
Hard coat solves wear. It does not solve friction, and plenty of parts need both. When a drawing calls for a hard anodic coating and a low friction surface at the same time, the coating can be impregnated with PTFE so the wear surface carries its own dry lubricant. That is a separate service line, commonly specified under AMS 2482, and the PTFE impregnated anodizing page explains how it is called out.
What a hard coat request for quote should include
Four things get you a cost the same working day:
- The print or a clear description. A PDF, a STEP file or a marked-up drawing, with the MIL-A-8625 Type III callout exactly as written.
- The process the part needs. Hard coat, sealed or non-sealed, clear, black or a named color, plus any masking.
- How many parts. Say whether the job repeats, because a one-off and the first lot of a standing order are quoted differently.
- The date you need them back. Optional, and worth adding anyway.
Two more details speed things up: the alloy, if you know it, and a one-line note on what the part does. If your customer requires documentation, say so with the request so the shop can confirm what it can provide before you accept the quote. On cost, there is no rate card. Minimum fees depend on required services, so each job is quoted from the print and the count.
Turnaround, expedites and getting parts to Paoli
Standard turnaround is 3 to 5 days from the day parts reach the dock, and the date goes on the quote. Expedites typically run 24 to 48 hours, and as fast as same day when the schedule allows; expedite requests are answered by text with a straight yes or no on your date. AnoPRO picks up and delivers within a 100 mile radius of Paoli, which covers Indianapolis, Bloomington, Columbus, Louisville, Evansville and Terre Haute, so parts move on the shop's own trucks with no crating and no freight terminal.
Frequently asked questions
Is hard coat anodizing the same as Type III or hardcoat? Yes. Hard coat, hardcoat, hard anodizing and Type III all describe the same process, and a drawing may use any of them.
Can a hard coated part be stripped and run again? Talk to the shop first. Stripping an anodic coating takes base metal with it, so a dimension-critical part may not survive the round trip. A non-critical part is usually straightforward.
Does hard coat work on tight tolerance parts? Yes, when the drawing accounts for the build. Put the coating allowance on the callout and the shop finishes to it.
What metals does AnoPRO hard coat? Machined aluminum parts only. Keeping the shop to one metal is part of why finish quality and turnaround both hold.
Ready to send a hard coat job? Request a quote from AnoPRO, LLC with the print, the count and a line about what the part does, and the date goes on the quote.