Finding the Right Grit for Cast Iron – Why Testing 30#, 60#, and 120# Diamond Wheels Makes All the Difference

2026,07,09

Introduction

Cast iron is one of the most common materials in industry.

Engine blocks and cylinder heads
Machine bases and heavy equipment
Pipe fittings and industrial castings
Brake rotors and automotive components

But grinding cast iron is not a one-size-fits-all job.

Different cast iron types – gray, ductile, chilled, malleable – have different hardnesses and grinding characteristics. And different operations – roughing, general grinding, finishing – require different grit sizes.

So how do you find the right grit for your application?

The answer: test them.

That's why we offer brazed Diamond Grinding Wheels in three grit options – 30#, 60#, and 120# – so you can test and determine the optimal grit for your cast iron grinding application.

In this article, we'll explain the differences between these grits, when to use each one, and why testing is the smartest approach to tool selection.

Part 1: Understanding Grit Sizes

Grit size refers to the size of the diamond particles on the grinding wheel. The smaller the number, the larger the particle.

Grit	Particle Size (approx.)	Cut Rate	Surface Finish	Best For
30#	~500-600 µm	⭐⭐⭐⭐⭐ Very aggressive	Very rough	Heavy stock removal, rough grinding
60#	~200-250 µm	⭐⭐⭐⭐ Aggressive	Medium	General grinding, conditioning
120#	~100-120 µm	⭐⭐⭐ Moderate	Smooth	Finishing, surface smoothing

The Rule of Thumb:

Rule	Explanation
Coarser grit = faster cut, rougher finish	Large particles remove more material per pass
Finer grit = slower cut, smoother finish	Small particles create a smoother surface
Work from coarse to fine	Start coarse, then move to finer grits for best results

Part 2: The Three Grits – When to Use Each

30# – The Heavy Lifter

Aspect	Description
Cut rate	Very aggressive – removes material fast
Finish	Very rough
Best for	Heavy stock removal, rough grinding, fettling

Typical Applications:

Operation	Why 30# Works
Removing gates and risers	Fast material removal
Grinding off casting flash	Aggressive cutting
Heavy stock removal	Removes large amounts quickly
Rough surface preparation	Prepares surface for subsequent grinding

When to Choose 30#:

✅ You need to remove a lot of material quickly
✅ You're working on rough castings with excess material
✅ You're doing fettling or foundry work
✅ Surface finish is not critical at this stage

60# – The General-Purpose Grit

Aspect	Description
Cut rate	Aggressive – good material removal
Finish	Medium
Best for	General grinding, surface conditioning

Typical Applications:

Operation	Why 60# Works
General grinding	Good balance of removal and finish
Surface conditioning	Smooths rough surfaces
Pre-polishing preparation	Prepares for finer grits
Edge grinding	Good edge quality

When to Choose 60#:

✅ You need a balance of removal and finish
✅ You're doing general cast iron grinding
✅ You want to smooth surfaces without excessive roughness
✅ You're preparing for a finishing operation

120# – The Finishing Grit

Aspect	Description
Cut rate	Moderate – finer cutting action
Finish	Smooth
Best for	Finishing, surface smoothing, final preparation

Typical Applications:

Author:

Ms. wang wenqin

E-mail:

support@hnkm-abrasives.com

Phone/WhatsApp:

++86 18838275294