McIver Engineering turns, mills and fabricates 304, 316, 431, 630 (17-4 PH) and 2205 duplex stainless at our Smithfield workshop, for food processing, medical, marine and general industrial work, from one-off parts to repeat batches.
Austenitic stainless does not behave like mild steel under a cutting edge. It has low thermal conductivity, so the heat generated at the cut stays in the tool and the chip instead of being carried away by the workpiece. That heat is what kills inserts, so cutting speed, coolant delivery and depth of cut are chosen to keep the edge working rather than to look fast in the cycle time.
The bigger issue is work hardening. Stainless hardens the moment it is deformed, so a light rubbing pass, a dwelling tool or a feed that drops too low leaves a hardened skin that the next pass has to fight through. The rule on the floor is to stay under that skin, keep a positive feed and cut in one committed pass rather than skimming. Interrupted cuts and tool dwell are designed out of the program for the same reason.
Chip control is the third factor. 304 and 316 produce long, tough, stringy chips that will wrap a turned part and score a finished diameter if they are not broken. We use insert geometries with a defined chip breaker, programmed peck cycles on deep holes and chip-breaking feed variation on long turns, so swarf clears the cut instead of welding itself to the tool.
The harder grades ask for different handling again. 2205 duplex is strong and tough, so it wants rigid work holding, reduced surface speed and a deliberate feed rather than a fast light cut. 431 and 630 are machined according to the condition the bar arrives in, which is why we ask whether 17-4 PH stock is solution treated or already aged before quoting. Stainless also grows measurably as it heats during a cut, so tight-tolerance bores and diameters are gauged once the part has stabilised rather than straight out of the chuck.
Food processing, pharmaceutical and wash down environments care as much about the surface as the dimension. A part that measures perfectly but carries a scratch running across the flow path, or a crevice at a joint, will hold product and fail on hygiene grounds. We treat surface condition as part of the specification, not as cosmetic tidying at the end.
Stainless is kept separate from carbon steel work so free iron is not pressed into the surface by shared tooling or abrasives, because embedded iron is what turns a stainless part rusty in service. Where machined parts are welded into assemblies, welds are dressed flush, linished to a consistent grain and passivated to restore the chromium oxide layer.
Internal corners, blind pockets and skip welds that cannot be cleaned are raised at drawing review rather than argued over at handover. If your part has a defined hygienic requirement, tell us at enquiry stage so the finishing route is priced in from the beginning.
On the lathes, the everyday stainless work is shafts, spigots, bushes, adaptors, threaded studs, sleeves and sealing faces. On the mills it is housings, mounting plates, manifold blocks, guide blocks, brackets and machined faces on fabricated frames.
On the fabrication side we make 304 and 316 benches, hoppers, chutes, product guards, covers and stainless framing, often combining laser cut and folded stainless sheet with turned or milled components that have to locate accurately.
Replacement and reverse engineered parts are a steady part of the work too. If a stainless component has failed and there is no drawing, send the part or what is left of it and we will measure it and machine a replacement.
We hold tolerances as tight as 0.01 mm on critical features in stainless. Tight tolerances are applied where the drawing needs them, on fits, bores, sealing faces and locating diameters, and opened up elsewhere so you are not paying for precision that does nothing for the assembly.
Finish in stainless is driven by how the cut is taken. A sharp edge with the right feed leaves a bright, consistent machined surface, while a worn edge smears rather than cuts and shows up immediately as a dull, torn finish. Finishing passes are run with dedicated tooling rather than the roughing edge, and turned parts are dressed and linished where appearance or cleanability matters.
Inspection is against your drawing, with critical features measured and recorded. If you need first article inspection or a dimensional report with the delivery, ask for it with your enquiry.
We machine 304 and 316 as our standard austenitic grades, 431 and 630 (17-4 PH) where hardness and higher strength are needed, and 2205 duplex where chloride resistance and strength have to come together. Material is bought in to your job, so tell us the grade and form you need with your enquiry and we will confirm availability before quoting.
Yes, both. 2205 duplex and 630 (17-4 PH) are grades we take on rather than turn away, and they are quoted with the cycle time they genuinely need. Duplex is strong and tough enough to need reduced speeds, rigid work holding and a heavy positive feed, and 17-4 PH is machined in the condition it is supplied in, so tell us whether your material is solution treated or already aged.
Yes, 316 is the more demanding of the two. The added molybdenum makes it tougher and more prone to work hardening, so it needs lower surface speeds, a heavier feed to stay under the hardened skin and uninterrupted cutting to avoid glazing the surface. That extra cycle time is normal for the grade and is priced into the job rather than discovered later.
Yes, passivation is done in our own workshop, so machined and welded stainless can be passivated as part of the job without going to another handler. Electropolishing is not something we do in house, so where a specification calls for it we arrange it with an outside finisher.
Yes. Stainless work is kept away from carbon steel so there is no iron pick up on the finished surface, with dedicated abrasives and tooling used on food contact parts. Welded stainless assemblies are dressed, passivated and returned with no heat tint or crevice left to hold product.
We hold tolerances as tight as 0.01 mm on critical features. Stainless holds size well once thermal growth during the cut is accounted for, so tight-tolerance bores and diameters are measured after the part has settled rather than straight off the machine.
Turned diameter and length, and the largest milled part, are set by our machining envelopes rather than by the material, so stainless is no more limited than any other grade we cut. Send the overall size with your enquiry and we will confirm it against our machines before you commit any engineering time.
Yes, we can supply mill certificates for stainless material we purchase for your job. Ask for certification at enquiry stage so the material is bought and recorded against your order from the start.
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