What's the difference between CCMT and CCGT carbide inserts?

The distinction between CCMT and CCGT carbide inserts lies primarily in the chip breaker geometry, edge preparation, and intended application—despite them often having the same basic shape and size. Here’s a breakdown:

Designation Format (ISO 1832)

Both CCMT and CCGT follow the ISO insert naming convention. The letters each mean:

• C: 80° rhombic shape (diamond shape)
• C: Clearance angle 7°
• M/G: Tolerance class
• T: Fixed with a screw

So the key difference is in the third letter:

• M = M class tolerance
• G = G class tolerance

However, when we compare CCMT and CCGT inserts in practical use, there are clearly many differences not summarized by a simple difference in the ISO designation. These are difference commonly found between CCMT and CCGT inserts that aren't indicated in the simple 4 letter designation:

1. Edge Geometry

• CCMT: Tends to have a honed or chamfered edge (slightly stronger), suitable for general turning, including roughing and semi-finishing. The edge can withstand interrupted cuts and harder materials.
• CCGT: Often has a razor-sharp, ground edge with a positive back-rake angle. It’s optimized for finishing and cutting on small low rigidity lathes, particularly in softer materials like aluminium, copper, brass, plastics, and sometimes stainless steel.

2. Cutting Force and Material Compatibility

• CCMT: Handles higher cutting forces; works well with ferrous metals like steels and cast irons.
• CCGT: Produces low cutting forces, which is ideal for thin-walled or flexible parts and softer materials. Often used with high rake angles and positive cutting geometries.

3. Surface Finish

• CCGT generally gives a superior surface finish due to its sharp edge.
• CCMT can also produce good finishes but may generate slightly higher cutting forces and burrs, especially in soft materials.

4. Cost and Wear

• CCGT inserts wear faster due to their sharpness and are more expensive due to precision grinding.
• CCMT inserts are more robust and economical for general use.

Summary Table

If you're choosing between them, the primary question is whether you need edge strength and versatility (CCMT) or low-force precision cutting with better finishes on soft materials (CCGT).