TPI for Metal-Cutting Blades: Thickness-Based Chooser and Variable-Pitch Made Easy

For metalworkers, the most crucial specification on a saw blade is not its length or width, but its TPI, or Teeth Per Inch. TPI determines how many teeth engage with the material at any given moment, directly impacting your cut speed, finish quality, and blade lifespan. A blade with the wrong TPI can strip teeth, cause excessive vibration, or result in a jagged, unusable cut. This guide will help you select the perfect saw blade for any metal-cutting job.

TPI and Tooth Engagement Basics

The fundamental rule of TPI is simple: you need at least three teeth in contact with the material at all times. If fewer than three teeth are engaged, the teeth can "hook" or "gouge" the material, leading to stripped teeth, blade damage, and a ruined workpiece. This principle is your primary guide for selecting the right TPI for the thickness of your metal stock.

Thickness-to-TPI Chooser

Selecting the right TPI is a simple formula based on the thickness of the material you are cutting.

Browse Benchmark Abrasives' full line of saw blades for wood and metal by TPI and material.

Variable-Pitch vs. Constant Pitch

Saw blades come in two main tooth configurations: constant pitch and variable pitch.

Constant Pitch

Blades with a constant TPI (e.g., 14 TPI) are ideal for cutting a single, consistent thickness of material. They offer predictable performance and are great for production work.

Variable-Pitch

These blades feature teeth with alternating TPI (e.g., a 10/14 TPI blade has a repeating pattern of 10 teeth per inch and 14 teeth per inch). This is the most versatile blade type. The alternating pitch helps to:

• Reduce Vibration: The irregular tooth pattern dampens harmonics, resulting in a smoother, quieter cut.
• Expand Versatility: A single blade can effectively cut a range of material thicknesses, which is especially useful for cutting hollow stock like tubing or angle iron. This allows the blade to engage with the thinner walls and the thicker corners without stripping teeth.

Tooth Forms and Set Patterns

The shape and arrangement of the teeth also impact performance.

1. Raker Set: The most common pattern for cutting solid materials. The teeth are set in a pattern of one right, one left, and one straight tooth, which creates a wide kerf and helps to clear chips.

2. Wavy Set: The teeth are set in a series of gentle waves. This pattern is ideal for thin-walled sections like sheet metal and tubing, as it distributes the cutting load and prevents stripping.

3. Alternate Set: Teeth are set alternately, one to the right, one to the left. This is a versatile set pattern for general-purpose cutting.

Material Playbook

• Mild Steel and Carbon Steel: These are relatively soft and easy to cut. Use a constant TPI blade that matches the material thickness.
• Stainless Steel: Stainless steel work-hardens quickly. To avoid this, use a slower blade speed and a constant, firm feed pressure. A variable-pitch blade with a positive tooth angle can help to prevent work-hardening.
• Aluminum: Aluminum is soft but can gum up the blade. Use a coarser TPI (lower number) and a lubricant to prevent chips from sticking.
• Tool Steel: This material is very hard. Use a fine TPI blade with a high-speed steel or carbide tooth and apply consistent feed pressure to avoid chipping.

Troubleshooting Common Issues