Bearing housings
A bearing bore and its mounting feet need to line up. Include the bore fit, center height, mounting-hole positions and the faces used to locate the housing.
Cast Iron CNC
Machining
Cast iron housings, bushings and fixture parts
Flanged bushings and sleeves
Specify the bore, outside diameter, shoulder and flange thickness together. Identify the surface that locates the sleeve and any allowance for a later finishing step.
Fixture plates and blocks
Flat support faces and repeated hole positions define the useful geometry. Show which surfaces can stay as cast and which need full machining.
Covers and bearing end plates
A cover may need a locating diameter as well as a flat contact face. Mark the seating area, bolt pattern and required relationship between the bore and face.
Guide blocks and wear strips
Show the sliding face, mounting features and the part it runs against. Include any required hardness, finish and lubrication conditions on the drawing.
Hubs and mounting flanges
The bore, locating diameter and bolt circle may use different machining operations. Identify the fit and any specified runout requirement relative to its datum.
Illustrative part forms. Send your drawing to discuss the actual grade, blank and machining scope.
Casting supply and blank sourcing
I have castings ready
Send the casting drawing, finished-part drawing, photos and available inspection records. Include the quantity ready to ship and the approximate weight of each blank. We can review the machining scope before you move the batch.
Review cast bar stock
A simpler sleeve, hub or block may start from continuous-cast stock instead of a dedicated shaped casting. Supply the stock dimensions and grade, and allow room for surface cleanup. Stock-size conventions depend on the supplier.[2]
Help me source a blank
Send the finished model, expected batches and any foundry or pattern information you already have. Blank sourcing is a separate scope to confirm, including the supplier, tooling ownership, incoming checks and responsibility for nonconforming castings.
Machining a casting is different from producing it.Confirm who supplies the blank and which operations, records and treatments are included in the order.
Gray iron, ductile iron and specified grades
Gray iron and ductile iron belong to the cast iron family, but they are not interchangeable. Gray iron has flake-shaped graphite; ductile iron has nodular graphite. The grade and matrix structure affect both the finished part’s properties and its machining behavior.[1]
Use the complete designation on your drawing, including the applicable specification and delivery condition. A request for “cast iron” alone leaves important choices open. Any material alternative should be agreed before purchasing the blank.
- Material identity
- Specification, grade and supplier records
- Blank form
- Shaped casting, continuous-cast bar or pre-cut blank
- Condition
- As supplied, treated or pre-machined, as specified
- Size review
- Overall envelope, weight and fixture access
Gray iron
Flake-graphite gray iron is used for its vibration damping and machinability. ASTM A48 Class 40 identifies a specific grade; blank records and machining allowance still need to be agreed.[3]
Ductile / nodular iron
Ductile iron grades define different property requirements. For example, 65-45-12 is a designation used under ASTM A536. Include the exact required grade, hardness or treatment condition rather than substituting by appearance.[4]
A specified or treated grade
Compacted graphite iron, austempered ductile iron and high-hardness grades need a separate machining review. Name the exact material and its incoming condition so tooling, finishing sequence and verification can be checked.[5]
Specify the cast iron grade and governing standard. Cross-standard substitutions require approval.
| Property | 65-45-12 ductile iron Dura-Bar 65-45-12 | Condition |
|---|---|---|
| Minimum tensile strength (ksi) | 65 | Longitudinal specimen,mid-radius |
| Minimum yield strength (ksi) | 45 | Longitudinal specimen,mid-radius |
| Minimum elongation (%) | 12 / 9 | Diameter≥2in / <2in |
Values apply to as-cast bar; minimum elongation is 12% for diameters of 2 inches or more and 9% below 2 inches.
Machining allowance and datums for cast iron parts
Machining allowance on every face
A nominal casting envelope is only a starting point. Check the material available on each machined face and around each bore, including the effect of casting variation. For cast bar, use the supplier’s cleanup allowance rather than assuming the marked size is the finished size.[2]
Choose accessible locating and clamping points
Choose support and clamping points that hold the actual casting steadily while leaving the first machining areas accessible. A rough surface used for initial location may later be removed or replaced by a machined reference.
Relate the bore and mounting holes to the machined base
For a bearing housing, the bore centerline and mounting holes may need to relate to the finished feet. Mark those datums and limits on the drawing. Check the finished relationships after all operations that can affect them.
CNC milling, turning and bore finishing
Mounting faces, slots and hole patterns
Milling establishes the faces and locations needed for assembly. On a casting, identify where a fully cleaned-up surface is required and where an as-cast surface can remain. That avoids removing material that does not help the part fit.
CNC milling servicesDiameters, flanges and shoulders
Turning suits sleeves, hubs and circular locating features. Show the surfaces that must run true to the specified datum, together with shoulder positions and bore limits. Allow for any later operation that changes a fit.
CNC turning servicesBores that locate another component
A cast opening may still need substantial machining before it becomes a controlled bore. Boring, circular milling or a separate finishing operation can be reviewed against the size, geometry, access and surface requirements.
Explore machined partsThe incoming material changes the cutting job. Gray iron can chip at an unsupported exit edge, while ductile iron’s matrix and hardness change tool selection. Blank condition, cutter access and edge treatment belong in the machining review.[5]
Check the casting and the finished dimensions separately
Bore position, flatness and datums
For a housing, a machined bore can look good while its center height is wrong. A cover can meet its thickness and still miss a flatness requirement. Name the functional dimensions and geometric requirements so the inspection plan follows the assembly.
If machining exposes a cavity or other unexpected indication, agree how the affected part is identified, documented and held for a decision. Define the disposition route before production; repair, impregnation or material substitution needs separate approval.
| Feature | Specification | Acceptance condition | Verification |
|---|---|---|---|
| Incoming blank | Material identity; machining stock; damaged areas; reports | Specified cleanup allowance | Incoming checks; disposition of insufficient stock |
| Bores and locating diameters | Size limits; form; datums; finish | Applicable drawing and general tolerances | Dimensional and surface checks |
| Mounting faces and hole patterns | Flatness/orientation; center height; hole position | Final reference faces; defined setup | Datum-referenced measurements |
| Casting condition | Defect criteria; material/NDT requirements | Specified method, coverage and acceptance | Material/NDT reports separate from dimensions |
| Treatment and final condition | Hardness; heat-treatment records; masks; final surfaces | Required records and responsible supplier identified | Separate test records, appearance and dimensions |
Coating boundaries and rust protection
Machined fits and contact faces
Show the bore, locating diameter, sliding face and any other surface that must be protected. Specify permitted edge breaks so deburring does not change a seat or corner that matters.
Paint and coating boundaries
Mark coated areas and masking boundaries on the drawing. Keep dimensional requirements tied to their final state, including whether an inspection occurs before or after coating.
Rust prevention and packing
Agree temporary protection that can be removed without harming the next process. Protect machined faces from contact damage and keep the part identity linked to its batch records through packing.
From the first sample to repeat cast iron batches
Review the blank
Check the casting or bar source, dimensions, grade and drawing revision before pricing the machining route.
Agree the sample check
Use an agreed first piece or sample batch to review cleanup, datum transfer, fits and the required records.
Release the batch
Keep the approved revision, material route and processing sequence with the order. Confirm changes before repeating the job.
Identify each shipment
Link part marking, packing labels and agreed reports to the released batch. Keep later finishing and shipment dates clear.
Compare the whole blank-to-part cost
A near-net casting can reduce stock removal but adds a foundry and tooling scope. Cast bar can avoid a dedicated pattern for some shapes while requiring more machining. Compare blank cost, fixture preparation, machining, inspection, treatment and batch quantity together.
Compare CNC quotation scopeBlank supply and machining responsibilities
VETCNC works with factories and partner companies in China. Confirm the blank supplier, machining scope and communication responsibilities before ordering.
Meet VETCNCCast iron CNC machining questions
Can cast iron be CNC machined?
Yes. Gray and ductile irons can be milled, turned and processed with suitable hole-making tools. The exact grade, structure and hardness affect the machining route.[1] Send your blank information and finished drawing to review the work with VETCNC.
Can you machine castings that I supply?
Customer-supplied castings are a route to review. Send blank photos, dimensions, weight, grade records and the finished drawing first. Agree the incoming acceptance checks and how nonconforming blanks will be handled before shipping them.
Do you supply the casting as well as the machining?
State whether you need machining only or help sourcing the blank. Any foundry or stock-supply arrangement must be confirmed separately, including patterns, supplier responsibility, material records and the acceptance of the blank.
What is the difference between gray iron and ductile iron?
Gray iron contains flake graphite; ductile iron contains graphite nodules. That structural difference affects mechanical behavior, and the matrix and grade affect machining.[1] Specify the required grade rather than treating the two names as interchangeable.
Can the part be machined from continuous-cast bar?
For suitable shapes, cast bar is an alternative starting point to review. It still needs the correct grade and enough stock for all machined surfaces. Compare the supplier’s size convention, cleanup allowance and available shape with the finished drawing.[2]
What tolerances can you hold on cast iron parts?
Start with the drawing’s limits and any applicable general tolerances. Highlight bore fits, datum relationships, flatness and surface finish. A commitment needs the actual material, feature size, blank variation and measurement plan, not one blanket tolerance for every part.
How much machining allowance should a casting have?
There is no single allowance for every blank. It depends on the casting process, shape, variation and surfaces to be cleaned up. Provide the raw and finished drawings together. For continuous-cast stock, confirm the supplier’s published sizing and cleanup rules.[2]
Does every cast iron part need stress relief or heat treatment?
No blanket treatment sequence should be assumed. Provide any specified treatment, final hardness and dimensional-stability requirements. The material supplier and machining team can then review where treatment belongs in the route and what finishing work follows.
What happens if machining reveals porosity or another casting defect?
Agree a process for identifying the affected part, documenting the location and holding it for review. Acceptance depends on the specified defect criteria and function. Repair, impregnation or use-as-is decisions need authorization; they are not automatic machining allowances.
What should I send for a cast iron CNC machining quote?
Send the finished model and drawing revision, raw casting or stock details, grade and condition, sample and batch quantities, critical dimensions, treatment and inspection requirements. Add blank weight and photos when available. The quotation should distinguish blank supply from machining.
Your cast iron blank and machining brief
Bring the raw blank and finished part together
A housing quote needs more than a finished bore diameter. Include the casting drawing, stock condition and the surfaces that locate the part during machining and inspection.
Use this brief to collect the details, then attach your files in the quote form. You can also download it for your own project folder.
Selected example
PROJECT SUPPORT
Discuss your cast iron part
Share your drawing, material and quantity. Tell us what you need and we will reply by email.
Related material and machining guides
Technical references
References for cast iron grades, terminology and machining considerations.
- Sandvik Coromant — Cast iron material groups
- Dura-Bar — Stock allowances and sizing conventions
- Dura-Bar — G2 gray iron and its ASTM A48 Class 40 reference
- Dura-Bar — 65-45-12 ductile iron and ASTM A536
- Sandvik Coromant — Milling cast iron grades
