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When sourcing CNC‑machined parts, furnish suppliers with a full‑detail RFQ. Missing dimensions, vague Material specs, or faulty CAD files cause endless follow‑ups, unforeseen costs, and production holdups.
A properly formatted CNC Machining RFQ enables manufacturers to comprehend all your technical specs ahead of production.
This article outlines the essential components of a standard RFQ file. Please use the provided checklist to improve communication with suppliers and obtain more accurate quotes.
1. What Is a CNC Machining RFQ Package?
A CNC machining RFQ package is a collection of technical files and order‑related purchasing information that buyers submit to manufacturers to obtain cost quotes for custom‑machined parts.
A typical RFQ package for custom CNC machined parts contains:
2D engineering drawings with measurements and tolerances
CAD files showing the part shape
Material type and condition
Surface finish and any extra processing needs
Number of parts needed and expected yearly usage
Quality inspection and documentation needs
Where to send the parts and when they are needed
Packaging, labels, and any special instructions
Not every project needs all the documents. Simple custom metal parts might only need a drawing and material details, while more complex precision parts may need detailed GD&T, inspection reports, and specific process needs.
The point is to give information so the manufacturer can quote the same product you want to buy.
2. Make a Complete 2D Engineering Drawing
2D engineering drawings serve as a vital piece of your CNC‑machining RFQ package. While 3D models display a part’s outer form, 2D drawings lay out key dimensions, tolerances, production requirements, and inspection criteria.
If no drawing is provided, fabricators can draw conflicting assumptions for the identical design, resulting in incomparable RFQ quotes.
2.1 Include All Important Measurements
Your CNC machining drawing should show the measurements needed to make and check the part.
Depending on the part, these may include:
Total length, width, and height
Diameter, depth and distance between holes
Thread size, pitch and depth
Width of slots, depth of pockets, and step sizes
Diameter of shafts, location of shoulders and groove sizes
Chamfers, radii and edges
Features that fit with parts and assembly measurements
For custom CNC turned parts, pay attention to diameter features that line up thread details and how far parts go in. For CNC milled parts, make sure hole positions, pocket depths, reference surfaces, and important geometry are clear.
Do not depend on measurements taken from a drawing. Every important measurement should be clearly listed.
2.2 Set Dimensional Tolerances
Tolerances show how much a manufactured measurement can change from the number on the drawing. They can have an impact on machining time, checking costs, and the total price of custom CNC machined parts.
For example, a general-purpose bracket may not need the level of measurement control as a precision shaft used in a tight fit.
Your drawing should show:
General tolerances for parts that aren't critical
Specific tolerances for important features
How parts fit together
Geometric tolerances where needed
Any special requirements for acceptance
Do not use very tight tolerances on every measurement without a reason. Tighter tolerances can mean steps in machining, more careful setup, special measuring tools, and more checking.
Instead, point out which measurements affect how parts fit, line up, seal, move, or work. This helps the manufacturer make the process while keeping important functions.
2.3 Use GD&T When Needed
Geometric Dimensioning and Tolerancing (GD&T) specifies form, positional, and alignment specifications that standard measurements fail to represent accurately.
GD&T proves highly beneficial for metal‑made parts such as shafts, flanges, bushings, mounting plates, and intricate housings.
Possible controls might include:
Position tolerance for holes and parts that attach
Perpendicularity between parts that fit together
Flatness for parts that seal or attach
Concentricity when needed
Circular or runout for parts that spin
Parallelism between reference surfaces
Set clear reference points and use a known drawing standard where possible. Only use the controls needed to show what the part needs to do. Many or conflicting tolerances can cost more without helping performance.
2.4 Say What Surface Finish and Edges Are Needed
Surface finish affects things like friction wear, sealing, how parts look, and how they fit together. If a specific roughness is needed, mark the surface and the value like Ra using a shared measurement standard.
Different parts on the metal component may need different finishes. A part that seals might need a different finish than a part that is not used much.
Also say if sharp edges are okay or if you need to remove burrs, round edges, or have specific bevels. If burrs could cause problems with fluid movement or safety, say that clearly.
3. Give the CAD Files for CNC Machining
3D CAD files help manufacturers see complex shapes, check how easy it is to machine, and plan the tools to use. They are very useful for custom CNC milled parts with features and designs that use both turning and milling.
The file type and how good the model is matter.
3.1 Choose the Right File Type
Common CAD formats for CNC‑machining RFQs include STEP, IGES, Parasolid, native CAD, and DXF. Most projects work best with STEP plus a dimensioned 2D drawing. Verify file integrity before sending to suppliers.
3.2 Check the Model Before Sending
An error or missing part in a CAD model can cause confusion during quoting and making the part. Before sending your files, make sure the following is true:
The model is the version that was approved.
The part is made to the size and units.
All features that are needed are there.
No gaps, missing parts, or extra shapes.
Threads, holes, grooves, and pockets match the engineering drawing.
The 3D model and 2D drawing are the same.
If something is hard to show in a model, use a detail view or section view in the drawing.
3.3 Keep the 2D Drawing and 3D Model the Same
The 2D drawing and 3D model have jobs. The model shows the shape while the drawing gives tolerance checking rules and other details.
4. Define Material Specifications for CNC‑Machined Components
Material choice impacts machinability, mechanical performance, corrosion resistance, component weight, surface finish, and overall part cost. Your CNC machining RFQ should specify precise alloy grades instead of generic terms like “steel” or “aluminum”. Common options include aluminum 6061/7075, stainless steel 303/304/316, carbon alloy steel, brass, copper, plus engineering plastics such as POM, nylon, and PEEK. Base your material selection on real‑world operating conditions and functional needs rather than chasing the cheapest available option.
For high‑spec CNC orders, add material temper, hardness values, and applicable industrial standards to your RFQ. Where material traceability is necessary, clearly list required deliverables including material test reports and certificates of conformity. Avoid requesting unnecessary certifications; extra testing and paperwork will raise expenses and extend production lead times.
5. Define All Mandatory Surface Finishes and Processing Steps
Many custom metal parts need more than just CNC Turning or milling to meet their needs.
Possible extra steps include:
Anodizing for aluminum parts that need it
Zinc plating for steel parts that need it
Passivation for stainless steel parts that need it
Electroless nickel plating or other coatings as needed
Heat treatment
Grinding or other finishing steps
Removing burrs and polishing
Marking, engraving, or laser marking
Assembly and special packaging
Also say if the measurements are for before or after surface treatment. Surface coatings will alter part dimensions, assembly fit, thread performance, and clearance tolerances. For components requiring mating assembly after plating or anodizing, suppliers must be notified of this requirement during process planning.
For functional surfaces, say if masking or special inspection after processing is needed.
6. Define Order Quantities and Order Placement Instructions
The amount you need has a big effect on the cost of CNC machining. A supplier who is making an order may plan differently than one who is making hundreds or thousands of parts.
Your RFQ should say what you need at first and what you expect later.
Add the following details if you have them:
How many parts for the sample
How many parts for the initial run
How many parts you expect to use each year
How often you will order
If you think the amount might go up later
If you will order more than one part number at the same time
For custom parts made by CNC machining, the lowest price per part is not always the choice. Think about setup charges, checking costs, risk of wasting time to make. If the supplier can keep the same quality when making more parts.
7. Make sure to say what quality checks and paperwork are needed
Quality needs should be clear before you ask for a quote, especially when making parts for companies or for things that need strict rules.
A full RFQ may say:
What measurements need to be checked
If First Article Inspection is needed
If reports on measurements are needed
If reports from a Coordinate Measuring Machine are needed
If documents proving the material are needed
If checking the surface texture is needed
If checking hardness or coatings is needed
If checking a sample or rules for accepting parts are needed
If tracking where parts came from is needed
If handling parts that do not meet standards is needed
Not every part needs a report. For parts, checking basic measurements may be enough. For parts that're complicated, with tight measurements or that must fit with other parts, more checking may be needed.
If your company has a quality rule or if the customer needs a certain way of checking, add the right paper or explain clearly.
8. Common Mistakes That Slow Down CNC Machining Quotes
Even smart buyers can miss things that stop makers from giving a quote.
Mistake 1: Not Being Specific About the Material
Words like "aluminum" or "stainless steel" do not say what kind or condition the material is.
Solution: Say the type of material and the rules it must follow. Add hardness, treatment, or certification needs when needed.
Mistake 2: Making All Sizes Too ExactToo
much exactness can cost more time and checking.
Solution: Find the parts that need to be exact and use exact sizes for others.
Mistake 3: Not Saying About Surface Treatments
A quote based on making the part may not include plating, painting, heat treatment, or other steps.
Solution: List all steps needed. Say if sizes are for the final part.
Mistake 4: Not Telling About How Many and Future Needs
A maker cannot plan best without knowing how many parts you need.
Solution: Tell how many you need now, how many in the run, and how many you might need later.
9. Get a Good Price for Your Custom CNC Machined Parts
Making an RFQ helps lower back-and-forth, avoid mistakes, and get better prices and lead time for making.
The main papers are usually a drawing, a 3D model, the right material, clear sizes, and the right amount.
For complicated parts, add details on surface treatments, checks, how the part is used, and how to send the parts. These details help the maker see the job, not just the making part.
At CNC Parts China, we help customers who need custom parts made by CNC machines and precise metal parts. Whether you need parts like shafts, bushings, screws, or other metal parts, a full RFQ helps our team understand your needs and find the way to make them.
Want to ask for a quote for your parts? Get your drawings, 3D files, material needs, how many you need, and any special checks, then talk to our team at engineer@cncpartschina.com or 8618998057602 for a check and a quote.
