Thread Cutting Pass Guidelines

When cutting threads with multiple passes, it's important to distribute the material removal evenly to balance cutting forces and improve tool life. Here's a guideline for pass distribution:

Two Passes: Cut approximately 65% of the thread on the first pass and 35% on the finish pass.

Three Passes: Use a 50/30/20 ratio for material removal.

Four Passes: Use a 40/27/20/13 ratio for optimal balance.

These ratios help to equalize the side cutting pressure, reducing tool wear and ensuring a smoother finish.

Multi-Start Threads & Thread Mills

Thread mills can be used for cutting multiple-start threads. For assistance, please contact our engineering team. Additionally, thread mills can be modified—cut off for shorter thread depths or necked back for deeper thread depths.

Adjusting Feed Rates for Internal Threads

To properly apply the Feed and Speed chart, it’s important to note that machining centers use the feed rate at the spindle’s centerline. This works for straight-line cutting, but when cutting internal threads, the feed rate must be recalculated to account for the geometry of the internal cut. Always adjust your feed rate accordingly for internal threading operations.

Let’s do this together: we’ll walk you through the setup and calculation of cutting parameters for a TM290-24A tool used to cut a 3/8-24 thread in stainless steel.

Tool Specifications:

• Tool Type: TM290-24A

• Thread Size: 3/8-24

• Material: Stainless Steel

• Tool Outside Diameter: 0.290 inches

• Chip per Tooth: 0.001 inches

• Number of Flutes: 4

Calculating Revolutions per Minute (RPM):

To determine the appropriate RPM for the tool, use the following formula:

Where SFM (Surface Feet per Minute) is 150 and the tool’s outside diameter is 0.290 inches.

So, the RPM calculation is: