Contact CNC Store Basic Steps: 5 Steps That Work
This guide is for design and sourcing engineers who need to reach out to a machine shop without wasting a week on email. It walks through contact CNC store basic steps: what to prepare, which questions to ask, and how to read a quote so you can judge whether the shop fits your part before you place an order.
In this article
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Key takeaways
What to prepare before you contact a CNC store
Most delays in the first week come from the buyer's side, not the shop's. A supplier cannot quote what it cannot see, and it will not guess at a material grade or a surface finish. Put the package together first, then send one complete message.
The minimum usable package is four items: a 3D model in STEP or Parasolid, a 2D drawing with tolerances and datums, the material grade, and the order quantity including spares. If the part has cosmetic requirements, add a photo or a sample of the acceptable surface.
Add an inspection note. Say whether you need a first article report, a material certificate, or dimensional data on every part. Shops plan inspection time differently when they know this up front.
Keep the drawing revision number in the file name and in the subject line. When a revision changes mid-quote, the shop can trace which version it priced. This one habit prevents a surprising number of disputes.
- 1ModelSTEP AP214 or Parasolid, one solid body per file
- 2DrawingPDF with GD&T, datums, and revision block
- 3QuantityPrototype count plus expected annual volume
- 4QualityFAI, material cert, or full dimensional report
How to screen a shop before you contact a CNC store
Capability comes before price. Open the shop's equipment list and match three numbers against your part: maximum travel, number of axes, and achievable tolerance. If your part is 900 mm long and the largest mill travel is 600 mm, the conversation ends there.
Check the tolerance statement carefully. A shop quoting ±0.005 mm on a 4,000 mm part is describing the machine, not the process. Thermal growth over that length is larger than the tolerance. Ask what tolerance they hold on your specific feature size.
Look at the materials list. Aluminum and mild steel are common. Titanium, Inconel, and beryllium copper are not. A shop that lists them has the tooling, coolant, and experience to cut them without burning tools.
Certifications matter by industry. ISO 9001:2015 covers general quality systems. IATF 16949:2016 applies to automotive, ISO 13485:2016 to medical, and ISO 27001:2022 to data handling. Match the certificate to your program, not to the shop's marketing.
Writing the first message that gets a fast answer
A good first message is short and structured. Lead with the part, the material, the quantity, and the deadline. Attach the model and drawing. Then list your questions as numbered points so the reply maps one to one.
Ask three technical questions in that first message. Which datums will you use for setup? How will you inspect the critical dimension? Who reviews the drawing for manufacturability? The answers separate a shop that quotes from a shop that engineers.
State your deadline as a date, not as "as soon as possible." A shop that knows the parts must ship by the 14th can flag a conflict immediately. If the schedule is tight, ask what they can do in 3–5 days and what has to wait.
Mention confidentiality early if the design is sensitive. Ask for an NDA before you send the model. A shop with a standard agreement will return it the same day. If the answer is vague, treat that as information.
Keep the thread in one email chain. Splitting the same RFQ across three threads and two phone calls is how a revision gets quoted at an old price.
Reading a CNC quote beyond the unit price
A quote has at least five numbers: unit price, setup or programming, finishing, freight, and lead time. Compare all five. A lower unit price with a separate programming charge and a longer lead time is often the more expensive option for a prototype.
Check what is included in inspection. If the price assumes a visual check and you need dimensional data on every part, the real cost is higher. Ask for the inspection plan in writing before you compare totals.
Watch the quantity breaks. On machined parts, the first piece carries most of the setup cost. The drop from one piece to ten pieces is usually steep; the drop from 500 to 1,000 is often small. Ask where the curve flattens so you order at the right step.
Finishing is the most common surprise line. Anodizing, electroless nickel, and laser marking all add cost and days. Laser marking needs a minimum character height of 1.5 mm to stay legible, so check your label design before you approve the finish.
Finally, ask what happens if a dimension is out. A written rework or replacement policy is worth more than a small discount.
Keeping the relationship working after the first order
Once a shop has your part history, the second order is faster. Keep one named contact on both sides. A process engineer who already knows the part will catch a revision problem before it reaches the machine.
Log the results. Record the actual lead time, the first-pass yield, and any inspection findings. After two or three orders you have real data instead of a feeling about the supplier.
Share forecast changes early. A shop that knows volume will double next quarter can reserve machine time. A shop that finds out on the day the PO arrives cannot.
When a problem appears, send photos and a measurement report rather than a description. Machinists solve problems from numbers. A photo with a caliper reading on the feature gets a fix moving the same day.
The 5 basic steps to contact a CNC store
Run these in order. Each one has a check you can complete before moving on.
- 11. Build the RFQ packageExport STEP, add a 2D PDF drawing with GD&T, write the material grade and quantity, and name the files with the revision number. Check: could a machinist quote this without asking you anything?
- 22. Shortlist three shopsMatch travel, axis count, tolerance, materials, and certifications to the part. Check: does the largest machine travel exceed your part's longest dimension with room for fixturing?
- 33. Send one structured messageState part, material, quantity, and deadline date. Attach both files. Ask about datums, inspection method, and DFM review. Check: are your questions numbered so each gets an answer?
- 44. Compare quotes on five linesUnit price, setup, finishing, freight, lead time. Request the inspection plan in writing. Check: is the cheapest quote still cheapest once finishing and inspection are added?
- 55. Confirm scope in writing before the POAgree on tolerance per feature, finish spec, inspection report type, and ship date. Sign the NDA if needed. Check: does the order confirmation repeat every number from the quote?
Which contact method fits which situation
Pick the channel that matches your part and schedule.
| Situation | Best channel | What to include | Watch out for |
|---|---|---|---|
| Simple bracket, loose tolerance | Online quote form | STEP file and quantity | Missing finish spec adds a round trip |
| Tight tolerance, ±0.005 mm | Email plus a call | Drawing with datums and feature list | Quotes without a per-feature tolerance note |
| Prototype, one piece | Email, no MOQ shop | Model, material, target date | Setup fees hidden outside unit price |
| Confidential design | NDA first, then files | Signed NDA before any upload | Vague answers about data handling |
| Repeat production, 10,000+ | Named engineer contact | Forecast, drawing revision history | Quantity breaks that never flatten |
| Exotic alloy, Inconel or Ti | Email with material callout | Grade, stock form, and heat treat | Shops without the material on their list |
Questions engineers ask before they contact a shop
What files does a CNC shop need to quote?
A STEP or Parasolid model plus a 2D PDF drawing is the standard pair. The model defines geometry; the drawing defines tolerances, datums, and surface finish.
If you have no drawing yet, send the model with a note listing the critical dimensions and their tolerances. The shop can quote, but expect a follow-up question about inspection.
How long should a quote take?
For a straightforward part with a complete package, a quotation and DFM analysis can come back within 12 hours. Complex geometry or exotic material takes longer because the shop has to plan the setup.
If you have sent a complete package and hear nothing for two days, send one short follow-up. Do not resend the files in a new thread.
Do I need an NDA before sending a model?
Ask for one if the design is not public. A shop with a standard non-disclosure agreement will return it the same day, and uploads should be handled as secure and confidential.
Send the NDA first, then the model. Once files are in an email thread, you cannot take them back.
Is there a minimum order quantity for prototypes?
It depends on the shop. Some accept a single prototype with no minimum order quantity and scale to 10,000+ part runs. Others add a setup charge that makes one piece uneconomical.
Ask directly. If one piece is possible, ask what the price is at 5 and at 50 so you can see where the setup cost flattens.
What tolerance can I realistically ask for?
On small features in aluminum or steel, ±0.005 mm is achievable with the right machine and inspection. On long parts, thermal movement and fixturing dominate, so the practical tolerance grows.
List tolerance per feature rather than one blanket note. General tolerances cover everything else and keep the price down.
What surface finish values should I put on the drawing?
As-machined surfaces typically fall in the Ra 1.6–3.2 μm range. A fine finish at Ra 0.2–0.8 μm needs extra passes or a secondary operation and adds cost.
Only call out a fine finish where it matters: sealing faces, sliding surfaces, or cosmetic exteriors. Marking the whole part with one tight value raises the price for no benefit.
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