How to Handle CNC Machine Work From Drawing to Shipment
This guide is for design engineers and buyers who need parts that hold tolerance the first time. It covers what to send, what to ask, and which checks catch problems before the spindle starts.
Key takeaways
How to Handle CNC Machine Inputs Before Quoting
Handling a CNC job starts before the machining question. It starts with what you send. A STEP file alone tells us the shape, not the intent. Without tolerance callouts we can only guess which surface matters, and guessing is how a part comes back for rework.
Send a 2D drawing next to the 3D model. The drawing should carry the datums you actually measure from, the tightest tolerance on the part, and any surface finish callout by area. If a bore needs Ra 0.8–1.6 μm and the rest can stay at Ra 1.6–3.2 μm as machined, say so. It changes the tool path and the cycle time.
State the material grade, not just the family. 6061-T6 and 6061 machine differently. So do 316L and 17-4PH. If the part sees heat, salt or body contact, name the grade and add any certification you need to keep on file.
Mark the critical features. Two or three dimensions that must hold matter more than fifty that can float. When we know which ones those are, we choose the machine and the fixture to protect exactly those features.
Run a DFM Pass Before You Release the Order
Design for manufacturability is not a sales step. It is the cheapest review you will ever pay for, because at this stage changes cost nothing but a redraw. At GreatLight the quotation and a free DFM analysis come back within 12 hours.
A DFM review looks at wall thickness, corner radii, thread depth, hole depth-to-diameter ratio and how the part will be held. A 0.5 mm wall in aluminium will chatter. A tapped hole that bottoms out at 3× diameter will break taps. These are fixable on the screen and expensive on the machine.
Watch for features that force an extra setup. A slot on the back face, a cross-hole at 30°, or a pocket that needs a long reach tool all add a re-clamp. Every re-clamp adds a small position error. Tolerance stack-up across four setups eats the budget faster than any single tight callout.
When the DFM notes come back, reply with decisions, not questions. Say which tolerance you can relax and which one is fixed by the mating part. That single reply often cuts both price and lead time.
Pick the Right Machine for the Geometry
Three-axis work is still the workhorse. Flat plates, blocks, brackets and housings with features on one or two faces run fastest on a 3-axis mill. Our 27 three-axis machines handle travel up to 750 × 1,150 × 550 mm and 600 × 600 × 600 mm.
Four-axis suits parts that need indexing: a shaft with flats, a manifold with ports around a bore, a housing with features on four sides. A Ø400 mm rotary table lets the part rotate while the tool stays in cut. Our 12 four-axis mills cover that range.
Five-axis is for two situations. Either the geometry is genuinely freeform, or the part has features on many faces and you want to avoid re-clamping. Our 16 simultaneous 5-axis machining centers cut impellers, medical housings and complex brackets in fewer setups. Fewer setups means less stack-up error.
Size decides the rest. For long parts we run a 4,000 mm maximum processing size, with travel up to 4,000 × 400 × 150 mm. Mill-turn centers handle parts that need both turning and milling, so a shaft with milled flats never leaves one machine.
Set Tolerances You Can Actually Hold
A ±0.005 mm tolerance is achievable, but not on every feature and not on every material. In aluminium with a rigid setup and light finishing passes, it is routine. On a thin stainless flange 300 mm across, thermal drift and tool wear make it a different conversation.
Call out the tight tolerance only where it matters. If a bearing bore needs ±0.005 mm, mark it. Let the mounting holes sit at ±0.1 mm. A drawing where everything is tight forces slow feeds, small stepovers and more inspection, and the price reflects all of it.
Tolerance interacts with finish. Holding Ra 0.2–0.8 μm requires a finishing pass with a sharp tool and stable coolant. That same pass also holds size better. If you need both a fine finish and a tight bore, say so, because we may leave grinding stock and finish on a grinder.
Note the reference temperature if your assembly is sensitive. A part measured at 20 °C and a part measured at 30 °C are not the same part. For long parts and mixed materials, state the inspection temperature so the numbers mean something.
How to Handle CNC Machine Work: 7 Steps
Follow in order; each step assumes the one before it is done.
- 11. Send a complete packageUpload STEP plus 2D drawing with datums, tolerance callouts, finish by area, material grade and quantity. Note any certification you need. Missing one of these delays the quote.
- 22. Read the DFM notes carefullyWithin 12 hours you get pricing and manufacturability notes. Check every flagged feature. Decide which tolerances can relax and which are fixed by the mating part.
- 33. Freeze the revisionConfirm one revision number and stop editing the model. A revision change after setup usually means scrapping the first article and re-quoting.
- 44. Agree on the critical featuresList the two or three dimensions that must hold, with their tolerance and measurement method. This drives fixture design and the inspection plan at ±0.005 mm where needed.
- 55. Confirm material and finishLock the grade (for example 6061-T6 or 316L) and the finish. Anodizing, electroless nickel or bead blasting all change final size slightly on tight features.
- 66. Approve the first articleFor new geometry, review the first article report before the run continues. Catching a datum error here costs one part instead of a lot.
- 77. Receive with inspection dataAsk for inspection reports with the shipment. Parts ship in 3–5 days for standard work; 100% inspection happens before shipment on every order.
Which Machine Handles Which Part
| Part geometry | Machine choice | Why it fits |
|---|---|---|
| Flat plate, features on one face | 3-axis mill | Fastest cycle, one setup, no rotation |
| Housing with features on four sides | 4-axis with rotary table | Indexes between faces without re-clamping |
| Impeller or freeform contour | 5-axis simultaneous | Tool reaches undercuts in one setup |
| Long beam, 4,000 mm class | Large-travel 3-axis | Fits the 4,000 × 400 × 150 mm envelope |
| Shaft with milled flats | Mill-turn center | Turning and milling in one program |
| Thin wall under 1 mm | 3-axis, light finishing passes | Rigid support, low cutting force |
| Tight bore at ±0.005 mm | 5-axis or grinder finish | Fewer setups, finishing pass holds size |
Questions Engineers Ask Next
How do I handle a CNC machine quote if I only have a 3D model?
Send the STEP file anyway. We can quote from the model for simple geometry.
For anything with fits or mating surfaces, add a 2D drawing. Tolerance intent is not visible in a solid model, and the quote will carry assumptions you may not want.
What tolerance can I expect on a first prototype?
On rigid aluminium parts with a clean setup, ±0.005 mm is achievable on critical features.
On thin walls, long parts or difficult stainless grades, expect looser numbers unless you accept extra finishing passes and longer lead time.
Do I need to pay for DFM analysis?
No. Quotation and a free DFM analysis come back within 12 hours.
The value is early: a chamfer or a radius change on screen costs nothing, while the same change after setup costs a re-quote.
How should I specify surface finish?
Give finish by area, not one number for the whole part. Ra 0.8–1.6 μm on a sealing face and Ra 1.6–3.2 μm as machined elsewhere is common.
If a face also carries a tight tolerance, mention both. The two requirements are machined together.
Can I order one part?
Yes. There is no minimum order quantity, from one prototype to runs over 10,000 parts.
One-off parts still get the same inspection before shipment, so the number on the report is real.
How do you protect my design files?
Uploads are secure and confidential. An NDA is available on request before you send anything.
We hold ISO 27001:2022 for information security alongside ISO 9001:2015 and IATF 16949:2016.
Send Your Drawing and Get a Real Answer
Upload a STEP file and drawing, and an engineer replies with price and DFM notes within 12 hours.
12-hour quote100% inspectionNDA on request
More machining notes
We publish setup notes, tooling trials and inspection data from the factory floor.
