Questions That Separate a Stainless Shop From a Shop

September 21, 2026

Most vetting advice is about certificates and machine lists. Those matter less than how a shop behaves before it has your money.

The questions that actually separate shops

1. Which stainless grades do you run in a typical month?

You are listening for specifics. 316L and 17-4 PH weekly, duplex occasionally is a real answer. We machine all materials is not. A shop that runs your grade regularly has parameters, tooling and scrap history for it.

2. What is your approach to work hardening on 316L?

You do not need to evaluate the technical answer. You need to hear that there is one. Sharp tools changed early, heavier feeds, rigid fixturing, high pressure coolant is the shape of a real answer. A blank response means the material is not routine there. Work hardening covers why this is the right question.

3. Do you passivate in house or send it out? To which standard?

The answer tells you about lead time and about control. In house citric to ASTM A967 with a copper sulphate test is a shop that understands the requirement. We can arrange that is a shop that will be quoting a subcontractor. Neither is wrong, but the second has a queue you cannot see. Citric against nitric.

4. What certificates can you return, and can I see a redacted example?

Mill certs with heat numbers, first article reports, passivation certificates. A shop that produces these regularly can show you one in minutes. A shop that has to think about it has not been asked before.

5. What would you change on this drawing to make it cheaper?

The single most informative question you can ask. A shop that knows the material will name two or three things: an internal radius, a tolerance that does not need to be tight, a finish note applied globally. A shop that says nothing either has not read the drawing or cannot see the cost drivers in it.

6. What on this part worries you?

The good answer names a specific feature. The deep pocket, the thin wall, the tolerance after ageing. A shop that says nothing worries them on a difficult part is either very experienced or has not looked.

7. What would you decline?

Shops that decline work have standards. A shop that takes everything is either very large or not being straight with you.

Red flags in the quote itself

It arrives immediately with no questions. On a drawing with any ambiguity, silence means assumptions. Those assumptions are in the price and you cannot see them.

It is much cheaper than the others. Check what is included. Usually the finish, the passivation certificate or the inspection is missing, and it will reappear later as a variation.

Passivation is priced without a standard named. They have quoted something. You do not know what.

Lead time is dramatically shorter than everyone else. Ask what is being subcontracted and whether that subcontractor has confirmed.

The quote does not restate the specification. A good quote tells you back what it thinks you asked for. That is your chance to catch a misreading before parts are cut.

They cannot say where the material comes from. On any part that needs traceability, this is disqualifying.

Certificates, and what they actually mean

ISO 9001. A documented quality management system exists and is audited. It does not mean the parts are good, it means there is a process for finding out when they are not. Adequate for most industrial work.

ISO 13485. The medical device quality system. Required for most regulated medical work. See ISO 13485 against ISO 9001.

AS9100. Aerospace, built on ISO 9001 with additional requirements around configuration control and counterfeit parts.

IATF 16949. Automotive, with heavy emphasis on production part approval and statistical control.

None of these tell you the shop is good at stainless specifically. They tell you it can document what it does.

Things that matter less than people think

Machine brands. A well maintained older machine in a shop that knows the material beats a new one in a shop that does not.

Shop size. A small shop can be the right answer for a complex low volume part and the wrong one for 5000 pieces. Match the shop to the job.

A slick website. No correlation either direction.

Being local. It helps with communication and shipping. It does not make a shop good at 316L.

Practical steps

1. Start with a small order where you can afford a problem. A validation batch tells you more than any audit.
2. Ask for a first article before the full run. On a new shop and a new part this is normal and reasonable.
3. Give the same complete package to every shop. Otherwise you are comparing scopes rather than prices. What to put in a stainless RFQ.
4. Keep the drawing under an NDA if it is sensitive, and ask before you send files.
5. Watch how they communicate under pressure. The shop that tells you early about a two day delay is worth more than the one that tells you on the due date.

How this works here

We are a matching service, not a machine shop. We read your RFQ and pass it to up to three shops that already cut your grades, so the vetting questions above are ones you put to them directly. We take no commission on the order and you deal with the shop you choose. Send your RFQ or see how it works.

Frequently asked questions

Figures in this guide are published specification limits or published typical values for the alloy, not measurements of any part. Machinability is rated against free-machining carbon steel B1112 at 100 and PREN is chromium plus 3.3 times molybdenum plus 16 times nitrogen. The conventions are set out in thereference section and the editorial standards.

Keep reading

• Which Quality System Does Your Machined Part Need?
• The Information a Stainless Shop Needs to Quote You