Where Stainless Quotes Go Wrong, and What Each Mistake Costs the Shop

For Shops / 25 Sept 2026

A stainless job that loses money rarely loses it on the shop floor. It loses it in the twenty minutes somebody spent producing the number.

Here are the seven assumptions that do the damage, what each costs, and the check that prevents it.

1. Quoting the cycle from carbon steel experience

The assumption: the part is a simple turned shaft, so the cycle time is roughly what mild steel would take with a modest uplift.

What actually happens: austenitic stainless work hardens as it is cut. Austenite transforms to martensite under strain, so a light pass or a rubbing tool leaves a hardened skin that the next pass has to cut through. Thermal conductivity is around 16 W per metre kelvin, roughly a third of plain carbon steel, so the heat stays at the cutting edge. And it is gummy, so built up edge forms, tears away and takes coating with it.

The cost: the handbook machinability index is 45 for SUS304 and 36 for SUS316 against 100 for free machining steel. If you quoted from an uplift of 20 per cent on mild steel, you are out by more than double on the cutting time, and your tooling consumption is worse than that.

The check: price stainless from stainless data. If you have not run the grade recently, ask the operator who last did, not the table.

2. Missing the general tolerance class

The assumption: the untoleranced dimensions are general tolerance, call it plus or minus 0.2 mm.

What actually happens: the title block said JIS B 0405-f. Class f is plus or minus 0.1 mm between 6 and 30 mm and 0.15 mm between 30 and 120 mm. Roughly half what you assumed, applied to most dimensions on the drawing.

The cost: finishing passes on faces you priced as roughed, and a first article that fails on dimensions nobody individually toleranced. Rework on a part that already carries all its machining value.

The check: read the title block before pricing. Ten minutes. The tables are here.

3. Ignoring the geometrical class

The assumption: if no geometric symbol is drawn, no geometric tolerance applies.

What actually happens: JIS B 0419 classes H, K and L apply by default. Class H run-out is 0.1 mm. Class H flatness on a 200 mm face is 0.2 mm.

The cost: a shaft turned in two operations that will not hold 0.1 mm run-out without a plan. Either a second setup you did not price or a part that fails inspection.

The check: the class letter is appended to the B 0405 note. Read both letters, not the first one.

4. Treating the finish note as decoration

The assumption: the general note says Ra 0.8, but that is boilerplate, the part is as machined.

What actually happens: it is not boilerplate, or worse, it is a legacy triangle mark that maps to Ra 0.2 and means grinding.

The cost: Ra 1.6 is free on stainless. Ra 0.8 needs attention and a tooling change schedule. Ra 0.4 usually needs an added operation. Ra 0.2 needs grinding with its own fixturing. Quoting as machined against a four triangle face is an operation you did not price.

The check: if the drawing has triangle marks, get the intended Ra confirmed in writing before you quote. Details in the surface finish guide.

5. Quoting heat treated parts as a single operation

The assumption: machine the SUS630 part complete, send it for aging, ship it.

What actually happens: aging contracts the part, typically on the order of 0.0005 to 0.001 mm per mm depending on temper. On a 100 mm dimension that is 0.05 to 0.1 mm, far outside a tight tolerance. On SUS440C, hardening distortion is larger and less predictable.

The cost: every toleranced feature is now out, and at 58 HRC you are grinding features you priced as turned.

The check: rough, heat treat, then finish. Always. Price two machining operations. If the drawing does not state the sequence, state it in your quote. See SUS630 and SUS440C and SUS420J2.

6. Absorbing the certificate requirement

The assumption: a certificate is paperwork, it costs nothing to include.

What actually happens: EN 10204 3.1 with heat lot traceability narrows which stock you can buy. The bar you had on the shelf may not qualify. On a small batch, the material becomes the largest line in the quote, and the lead time moves.

The cost: on 10 pieces, potentially more than the machining.

The check: ask what the certificate has to name before you price, and quote it as a line. The certificate guide covers the types.

7. Under-quoting the thin wall or the deep hole

The assumption: a 1 mm wall is a wall, and a 40 mm deep 5 mm hole is a hole.

What actually happens: the wall deflects, so the cut gets shallower, so the tool rubs, so the surface work hardens, so the next pass is worse. Residual stress released during machining moves the part after it comes off the machine, sometimes overnight. The 8D hole needs through coolant or a peck cycle that doubles the drilling time.

The cost: scrap on the first articles, a fixture you did not price, and a stress relieving operation you did not plan.

The check: calculate the ratios. Wall height to thickness over 10:1 is difficult. Hole depth to diameter over 5D needs through coolant. Both are in the thin wall and deep hole guides.

The pattern

Every one of these is the same failure: pricing the part you assumed from the part you glanced at.

The fix is a fixed ten minute routine before any stainless number goes out:

General tolerance class, both letters
Projection symbol
Finish call-outs, including legacy marks
Material standard and certificate level
Thread classes
Heat treat sequence, if any
Ratios: wall thickness, hole depth, internal radii
Outside processes and whose queue they sit in

Anything you cannot resolve becomes a question to our engineer, not a margin. A blanket risk margin loses you work you could have done well, and it does not actually cover the thing that goes wrong.

Requoting when scope changes

One habit worth building: when a requirement arrives after the quote, requote in writing. A certificate added, a finish tightened, a quantity halved. In our network the change comes from our engineer, because the buyer changed something with us, and we requote the buyer on the same basis.

Absorbing it silently teaches everyone upstream that scope is free, and the next change will be larger. Requoting with a clear reason keeps the price honest in both directions, and it is the shop that requotes politely and promptly that keeps the repeat work.

If your shop cuts stainless to JIS grades and you want orders that arrive already read, join the network. Registration costs nothing, there is no exclusivity, and you are paid on terms agreed in writing before your first order.

Questions shops ask

What is the most expensive quoting mistake on stainless?

Quoting the cycle time from carbon steel experience. Austenitic stainless work hardens and holds heat in the cutting edge, so the same geometry takes far longer and consumes more tooling than the feed and speed table suggests.

Should I add a risk margin to unfamiliar drawings?

Only when you cannot resolve the unknown. A blanket margin loses you work you could have done well. Ten minutes on the title block usually removes the thing the margin was covering.

How much stock should I leave for finishing on SUS316L?

Typically 0.3 to 0.5 mm on diameters, so the finish pass cuts fresh material rather than the hardened skin the roughing pass left. Cutting lighter than the hardened layer is what causes the tearing.

Is it worth requoting when scope changes?

Always, and in writing. A certificate requirement added after the quote changes which bar you can buy. Absorbing scope silently teaches the buyer that scope is free.

Cut stainless to JIS grades?

Join the network and the orders come from us: a purchase order from SUS CNC, a drawing that has already been read, payment on written terms. No listing fee, no exclusivity.

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