Introduction
Starting-point cast iron calculator for milling across gray iron, ductile iron, malleable iron, and CGI. Use dedicated drilling, turning, and boring workflows when the process changes.
How It Works
Enter the planning inputs for this calculator, review the computed output, and compare the result against your machine limits, tooling, material, and shop-floor validation workflow.
Key Formulas
Use the formulas, assumptions, and process notes on this page to validate the result before applying it to a quote, investment case, or live machining setup.
How to Use
Follow the step-by-step guidance, worked examples, and caution notes on the page before locking in the final numbers for production or procurement.
Related Calculators
Use the related calculator links on this page when the current workflow needs a more specific model for speed, feed, cost, capacity, maintenance, or machine selection.
Cast Iron Speeds & Feeds Calculator 2026
Set a first-pass RPM, chip load, and feed for cast iron milling across gray, ductile, malleable, and CGI grades. Route turning, drilling, boring, and reaming to their dedicated workflows before release.
Calculate Cast Iron Milling Parameters
Cast Iron Milling Guide
Search intent around cast iron feeds and speeds usually starts with milling questions: how hard the graphite structure will abrade the insert, whether to stay dry, and how to keep dust under control without creating slurry. That is the real scope of this page. It is strongest for first-pass cast iron milling across gray iron, ductile iron, malleable iron, and CGI. Turning, drilling, boring, and reaming should move to their dedicated workflows before release because feed-per-rev, boring-bar stability, and tool-geometry decisions change the safe answer.
What This Page Covers Best
First-pass cast iron milling parameters where graphite structure, dust behavior, edge abrasion, and coolant strategy determine whether the cut is stable.
Where It Needs Backup
Turning, drilling, boring, and reaming all need feed-per-rev logic or stability checks this milling model does not represent. Deep-hole dust evacuation also needs process-specific validation.
Best Next Links
Use the main feeds and speeds calculator when you need the broader RPM, chip load, MRR, and power workflow. Use the face-mill chart, drilling calculator, turning calculator, or boring bar calculator when the workflow gets more specific.
Cast Iron Types
Gray Iron
Graphite: Flake structure
Most common type. Graphite flakes interrupt the matrix, making it brittle but easy to machine. Excellent vibration damping. Produces fine graphite dust.
- • Class 20-30: Soft, easy machining
- • Class 40-60: Harder, slower speeds
- • Best machined dry or with air blast
Ductile Iron
Graphite: Spheroidal nodules
Also called nodular or SG iron. Round graphite nodules give ductility and higher strength than gray iron. Machines more like steel than gray iron.
- • 60-40-18: Ferritic, easy machining
- • 80-55-06: Pearlitic, moderate
- • 100-70-03 and up: Similar to steel
CGI (Compacted Graphite Iron)
Graphite: Vermicular (worm-like)
75% stronger than gray iron with 2× fatigue strength. Used in diesel engines. Extremely abrasive! Tool wear is 5-10× faster than gray iron.
- • Requires CBN or SiAlON ceramic
- • Reduce speeds vs gray iron
- • Production challenge
Malleable Iron
Graphite: Temper carbon nodules
Created by heat treating white iron. Good ductility and shock resistance. Machines well, similar to gray iron. Used for pipe fittings and hardware.
Cutting Speed Reference
| Grade | Machinability | Milling (m/min) | Turning (m/min) | Notes |
|---|---|---|---|---|
| Gray 20-30 | 100-110% | 150-350 | 190-420 | Easy machining |
| Gray 40-60 | 65-85% | 80-190 | 100-240 | Harder, slower |
| Ductile 60-40 | 80% | 130-280 | 160-360 | Similar to mild steel |
| Ductile 100-70 | 55% | 75-165 | 95-215 | High strength |
| CGI | 50% | 70-160 | 90-200 | Very abrasive! |
* Speeds for coated carbide (Al₂O₃). Ceramic can run 2-3× faster. The turning column is reference-only on this page; validate any real turning or boring setup in the dedicated calculators before release.
Tool Selection Guide
Carbide Inserts
Al₂O₃ (Alumina) coating is best for cast iron - excellent abrasion resistance. TiCN is also good. Use K-grade (uncoated) or Al₂O₃ coated grades.
Ceramic (High Speed)
Si₃N₄ (silicon nitride) and SiAlON excel at high-speed roughing of gray iron. Can run 500-1000+ m/min. Avoid flood coolant - thermal shock risk.
Frequently Asked Questions
Gray iron has graphite in flake form, making it brittle but excellent for damping (machine beds, engine blocks). Ductile iron has spheroidal graphite nodules, giving it ductility and higher strength, more similar to steel. Gray iron is easier to machine but produces more dust.
Continue The Cast-Iron Workflow
Use these tools when the job branches from cast iron milling into face milling, drilling, turning, or boring.
General Feeds & Speeds
Return to the main CNC feeds and speeds calculator for RPM, feed rate, chip load, SFM, MRR, and power context.
Face-Mill Chart
Quick-reference insert-based milling windows when the cast iron job uses a face mill instead of an end mill.
Drilling Calculator
Switch here for cast iron drilling feeds, peck cycles, and chip evacuation decisions.
Turning Calculator
Use feed-per-rev, diameter-at-cut, and insert-style logic for cast iron turning.
Boring Bar Calculator
Validate bar rigidity, overhang, and finish risk before releasing cast iron boring data.