Ordering
custom CNC machining parts is straightforward when the enquiry contains the right information and painful when it does not. Most disputes about custom machined parts trace back to something that was never stated — a finish, a datum, a report format, a packing method.
This checklist sets out what to specify, what to expect back, and what to verify on arrival. It follows the customisation process used by Changzhou Yuqing Heavy Industry Machinery Co., Ltd. (Yuqing Heavy Machinery) in Changzhou, Jiangsu, China.
What "Custom" Actually Covers
Custom CNC machining is not one service. It is four decisions made in sequence:
1. Geometry — a part designed for your application rather than selected from a catalogue
2. Material — a grade chosen for the service condition, not the nearest stock item
3. Process — the machining route, plus any heat treatment and surface treatment
4. Packaging — protection and marking that matches the transport mode and the destination
A supplier who only asks about the first one will produce a part that fits and fails in service.
1. Drawing Formats and Review
Send the model in a format the supplier can actually program from. Yuqing accepts CAD, SolidWorks, UG and Pro/E files, and works from both 3D models and 2D drawings.
Include on the drawing:
• Material grade and condition
• General tolerance note, plus individual tolerances on critical features
• Datum callouts
• Surface finish (Ra) on functional faces
• Heat treatment and surface treatment specification
• Any marking or traceability requirement
Expect process optimisation suggestions back. A supplier reviewing a drawing properly will usually find one or two features that can be relaxed or re-approached to save cost without changing function.
2. Material Selection
Common Traps in Grade Choice
Material should follow the service condition. The common ranges:
|
Requirement |
Material options |
|
General structural, low cost |
Q235, 45# carbon steel |
|
Corrosion resistance |
201, 304, 316, 316L stainless steel |
|
Lightweight, high strength |
6061, 6063, 7075 aluminium; AZ31B magnesium |
|
Electrical or thermal conductivity |
Copper, brass, bronze |
|
High load, high temperature |
40Cr, Cr12MoV, titanium alloy, high-temperature alloy |
|
Insulation, low friction |
POM, PTFE, nylon, PEEK, acrylic, bakelite |
Two common traps. Aluminium 7075 has excellent strength but is generally not welded, so a part that gets welded after machining needs 6061. And 316L work-hardens if the feed rate is too light, so cycle time — and price — is higher than 304 for the same geometry.
3. Tolerance Classes
Spending Tolerance Where It Matters
Apply tight tolerance where it does something and general tolerance everywhere else. That is the single largest cost lever available to a buyer.
|
Class |
Range |
Use |
|
General |
±0.2 to ±0.5mm |
Non-mating faces, clearance features |
|
Commercial precision |
±0.05 to ±0.1mm |
Most mating and locating features |
|
Precision |
±0.01 to ±0.02mm |
Bearings, seals, alignment |
|
Ultra precision |
±0.005mm and finer |
Only where function demands it |
Yuqing holds tolerances within ±0.005mm on precision custom work, with finer results achievable on specific features using precision grinding and lapping. Standards can be set to ISO GPS, ASME Y14.5, DIN or JIS depending on the destination market.
4. Surface and Heat Treatment
Post-processing is specified on the drawing, not agreed verbally. Name the process, the thickness or coating weight, the surfaces to be masked, and the colour if appearance matters.
Available at Yuqing: electroplating in zinc, chrome and nickel, anodising, passivation, painting, hot-dip galvanising, plus precision forging, sheet metal bending, surface grinding and polishing. Heat treatment is sequenced before finish machining so that distortion is corrected rather than discovered.
5. What Should Come Back With the Parts
The Inspection Package
Ask for the inspection package before you place the order, not after. A complete set for custom machined parts normally includes:
• Full-dimension CMM report on critical features, with measured values
• Surface roughness measurements
• Hardness test results where heat treatment applies
• Metallographic analysis for critical parts
• UT, RT or MT reports for welds and castings
• Material certificates
Yuqing provides full-size CMM testing, roughness testing, hardness testing to Rockwell or Brinell, metallographic analysis and non-destructive testing, with quality systems aligned to ISO 9001, TS 16949 and AS9100 requirements.
6. Size Range and Where the Supplier Fits
A custom part shop needs to cover both ends of the size range. Yuqing's capability runs from micro precision electronic components to large engineering machinery structural parts, with gantry machining centres up to 6000 × 13000mm and floor-type boring and milling machines handling bores from 20mm to 500mm and deep holes to 2000mm.
If your part set spans small fittings and multi-tonne frames, sourcing both from one supplier removes the interface problems that appear when two vendors machine features that have to match.
7. Packaging for Export
Custom parts often travel far, and damage in transit is expensive to resolve. Yuqing uses damage-proof export packing — vacuum packaging, foam protection and wooden pallets — suitable for sea, air and land transport and compliant with international logistics requirements.
Specify the packing requirement if you have one. Heavy parts need a pallet rated for the load, and parts with machined faces need protection that does not itself mark the surface.
8. Questions to Ask Before Ordering
1. Which machine will run my part, and what is its working envelope?
2. What tolerance can you hold across the batch, not just on the sample?
3. Who does the heat treatment and surface treatment — in house or subcontracted?
4. What inspection report will I receive, and does it include measured values?
5. What is the packing method, and is it suitable for my transport mode?
6. What is the process if a part is found out of tolerance on arrival?
Working With Yuqing Heavy Machinery
Changzhou Yuqing Heavy Industry Machinery Co., Ltd. has been machining and casting since 1989. The company operates a 10,000m² plant in Xueyanqiao Town, Wujin District, Changzhou, Jiangsu, with more than 70 staff and over 30 pieces of equipment, holds ISO certification, and was recognised as a national high-tech enterprise in 2025. Customers are located across China as well as in the United States, Japan, South Korea, India, Thailand, Finland and Germany.
For bespoke
CNC parts made to your drawing, contact sales@czyqzg.com or call +86 13906152937.
