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Medical CNC Machining: What to Ask Before You Send a Drawing

September 21, 2026

Most machined medical components are not hard to cut. A bone screw is a turned part with a thread. An instrument jaw is a milled part with a few tight features. Any competent shop can hold the geometry.

What a device company is actually buying is the evidence that the part was made the way the drawing said, that the material is what the certificate says it is, and that nothing will change quietly between this lot and the next one. That is the part general shops underestimate, and it is where most supplier relationships go wrong in month eight rather than week one.

This guide covers what to look for, what belongs on the drawing and what to put in the RFQ.

What changes against general machining

Four things, and only one of them is about cutting metal.

The quality system. ISO 13485 is not ISO 9001 with a medical sticker on it. It is built around risk management, traceability and holding a validated process still. A shop that improves its process every quarter is doing exactly what ISO 9001 asks and exactly what your device master record forbids without a change notice.

Traceability. The heat or lot number on the mill certificate has to survive every operation and come back out on the certificate of conformity. If a supplier cannot tell you which bar a screw came from two years later, you cannot run a recall and neither can they.

Validation. Where you cannot fully verify the result by inspecting the finished part, the process itself has to be validated. Cleaning and passivation are the usual cases. You cannot inspect a part and see whether the passivation bath was in spec, so the bath is validated and recorded instead.

Change control. No new tool coating, no different coolant, no moved sub-tier supplier without telling you first. This is the single most common cause of a supplier problem that nobody sees coming, because the part still measures fine.

Choose by part family, not by the word “medical”

A shop that runs 4 mm cannulated screws on Swiss lathes all day is not the shop for a robotic arm casting, and neither of them is the shop for a PEEK fluidic manifold. Medical is not a capability. It is a customer group.

• Orthopedic and trauma. Swiss turning and 5-axis milling in Ti-6Al-4V ELI and cobalt chrome. Cannulation, thread forms and surface finish on the bearing side.
• Surgical instruments. 17-4 PH and martensitic stainless, made to survive several hundred autoclave cycles without pitting or losing an edge.
• Dental. CP titanium and cobalt chrome, where the connection geometry between abutment and implant decides whether the part is usable at all.
• Endoscopy and minimally invasive. Small diameter and thin wall, where a burr is a patient safety issue rather than a cosmetic one.
• Robotics and capital equipment. Larger parts where positional tolerance across the whole envelope, not any single feature, sets the price.
• Diagnostic and lab. PEEK, PTFE and 316L, where internal surface cleanliness matters more than anything you can see.

Ask a candidate supplier which of these they do every week. The honest ones will name two.

Put the material standard on the drawing

The most expensive quoting mistake in this niche is writing an alloy name without the standard behind it.

Ti-6Al-4V and Ti-6Al-4V ELI released to ASTM F136 are not the same purchase. The ELI grade has controlled interstitials and comes with a certificate that ties the bar to a heat. Commercial Grade 5 to AMS 4928 is a different material at a different price, and a shop quoting against the wrong one will be cheaper every time.

The same applies down the list. 316L is a stainless steel. 316LVM released to ASTM F138 is a remelted implant bar with a certificate. PEEK is a polymer. Implant grade PEEK to ASTM F2026 is a traceable lot with a compliance history behind it.

Write the standard. If you do not know which one applies, write the requirement instead and let the supplier propose the grade.

What to send with the RFQ

A supplier who has to email you twice before quoting will quote in week two, not day two. Send this the first time:

Item	Why it changes the quote
STEP file plus a PDF drawing	The model gives geometry, the drawing gives intent, tolerance and notes
Material and its standard	Sets the bar cost and whether the shop can even source it
Tightest tolerance and where	One ±0.005 mm feature can change the whole process route
Surface treatment	Passivation, electropolish, anodising and polishing are separate operations with separate lead times
Cleanliness and packaging	A controlled clean and a double bag are hours, not an afterthought
Marking requirement	A UDI mark that has to survive passivation and autoclaving is not the same as a part number
Quantity, this order and annual	Fixturing that is worth it at 2,000 per year is not worth it at 50
Quality requirement	ISO 13485 required, preferred or not needed changes which shops can even bid
Drawing revision	If the part is on a device master record, say which revision you want quoted

Red flags when you talk to a shop

• They call ISO 13485 “basically 9001” or say the certificate is “in progress” without a date and a body.
• They cannot describe their change control process in one sentence.
• They quote passivation and cleaning as free extras rather than as operations with records.
• They say yes to every part family you mention.
• They offer to hold your validated process and also to keep improving it.

What is yours and what is theirs

Supplier qualification, the audit, the quality agreement and the decision to accept the supplier into your system are yours. They are part of your quality system and no intermediary can do them for you.

What you can outsource is finding the two or three shops worth spending that effort on. That is what this site does. We read the RFQ, we check that each shop holds a current certificate before it sees a preview, and we pass you to shops that run your part family. Your qualification starts there rather than with a search engine results page.

Once the part family and standard are chosen, the medical machining quote guide takes you through the RFQ, the quote lines and the comparison.

Frequently asked questions

Keep reading

• In-house vs outsourced machining for medical device components
• Common Mistakes When Sourcing a Machined Medical Component