Oct 13, 2026CNC Machining Tips
How to Prepare Drawings for a CNC Machining Quote (Checklist)
What to include in a CNC drawing to get an accurate quote fast — material, tolerances, surface finish, quantity and critical notes, plus a pre-send checklist.
A CNC machining quote is only as accurate as the information behind it. When a drawing is complete, the supplier can price real operations — material, machining time, fixturing, finishing and inspection. When key information is missing, every supplier does one of two things: adds a risk buffer to the price, or emails you questions and delays the quote. Neither is good for your project.
Key takeaways
• A complete RFQ package = material grade + marked tolerances + finish + quantity + inspection needs.
• Tolerance only what functions — blanket tight tolerances on every dimension raises cost with no benefit.
• STEP for the 3D model plus a vector PDF drawing is the standard machining-quote package; STL is for 3D printing only.
• Complete packages get engineering review and pricing back within 24 working hours — missing info costs a round of emails.
The good news is that preparing a complete drawing package takes about half an hour once you know what to include. This guide covers the eight items our engineers look for in every RFQ, plus a pre-send checklist you can run in under a minute.
The eight things every RFQ drawing should contain
1. Material grade and heat treatment
Specify the grade, not just the family. "Aluminum" is not a specification — 6061-T6 and 7075-T6 differ in strength, finish and price, and "stainless steel" ranges from 303 to 17-4PH. Write the grade and temper: for example 6061-T6, 7075-T6, 304, 316L, 17-4PH H1025, brass C3604, POM or nylon. If you are unsure, say so in the RFQ and ask for a recommendation — our engineers suggest a grade for free with the quote.
If you require material certificates (mill certs) or a specific material origin, state it now. It affects sourcing and lead time, and it is much cheaper to include at quoting than to request after production.
2. Tolerances — mark the critical ones
Mark every dimension that matters with its tolerance, and add a general tolerance note for everything else (for example ISO 2768-m). This is the single biggest cost lever in a drawing: a part with all-tight tolerances needs slower feeds, more setups and more inspection, while a part that tolerances only what functions prices dramatically lower.
A practical rule: tolerance the fits and interfaces, leave the rest general. If a dimension is untoleranced but actually critical, say so in a note — suppliers cannot guess which numbers matter.
3. Surface finish and treatment
State the finish for every visible surface: as-machined, bead blasting, anodizing (with color and gloss level), powder coating (with RAL code), passivation, zinc plating, QPQ or painting. For anodized parts, note whether color matching across parts and batches matters — it changes the process control required. If only cosmetic surfaces need a finish, mark them; finishing every surface of a hidden bracket is wasted budget.
4. Quantity and order structure
Give the quantity for the immediate order and, if possible, your expected annual usage. Unit price in CNC machining falls with volume because programming, fixturing and setup are spread across more parts — a 100-piece run typically costs far less per part than a 5-piece run. Quoting both a prototype quantity and a batch quantity in the same RFQ often saves a second round of emails later.
5. Threads, holes and features that need callouts
List thread specifications (for example M3x0.5-6H, M5x0.8, 1/4-20 UNC), thread depth, and any tight-tolerance holes for press fits or bearing seats. Note countersinks, counterbores, deburring requirements and any sharp edges that must be removed or kept. If a hole must be reamed or honed, say it — the tolerance on the hole diameter alone does not tell the supplier the process.
6. Critical features and inspection requirements
If you need a dimensional inspection report, first-article inspection (FAI) or a specific sampling level, include it in the RFQ. Inspection is a real cost, and it is much easier to price upfront than to retrofit. For regulated industries such as medical or automotive, state the standard and the documentation you expect.
7. File formats we accept
3D models: STEP or STP is preferred; IGES is acceptable. 2D drawings: PDF (vector, not scanned) or DWG/DXF. STL files are for 3D printing, not for machining quotes — they lose the exact geometry definitions that CAM programming needs.
Keep file names clear and versioned, for example bracket-A-rev3.step plus bracket-A-rev3-drawing.pdf. If the 3D model and the 2D drawing disagree, the drawing wins unless you state otherwise — so make sure they match before sending.
8. Commercial notes that avoid surprises
Include the delivery destination, required date, packaging requirements and any NDA or confidentiality terms. If your deadline is driven by a trade show, an assembly build or a customer commitment, share that reason — suppliers can often compress a schedule for a known cause, but not for a mystery.
The 60-second pre-send checklist
Material and grade named, with temper and certificate needs? Tolerances marked on critical dimensions, with a general tolerance note? Finish specified per surface, with color codes? Current quantity and expected annual volume? Threads and press-fit holes called out? Inspection and documentation requirements stated? Files in STEP plus PDF, clearly versioned, 2D and 3D consistent? Shipping destination and deadline included?
What happens after you send the RFQ
For a complete drawing package, expect a quotation with engineering notes within one working day. Our review includes a manufacturability check (DFM): if we see a feature that will be slow or risky to machine, we flag it with a suggested change — sometimes with a lower price next to it. If the package is missing information, we ask once, in one email, rather than sending questions out over a week.
Mistakes that slow quotes down
The most common ones: blanket tight tolerances on every dimension; missing material or finish; a 2D drawing that disagrees with the 3D model; STL files sent for machining quotes; and "quantity: to be decided". Each of these costs you a day of back-and-forth. None of them costs anything to avoid.
Send your drawings, get a quote within 24 hours
Email your drawings to info@prolathe.com or use the contact form. We quote CNC turning, CNC milling, sheet metal fabrication and 3D printing from prototype to low-volume production, with material certificates available on request. Your drawings and project details stay confidential.
