G76 Fanuc Threading Cycle, And Depth Of Cut In CNC Threading

Skip to content G76 Fanuc threading cycle, and depth of cut in CNC threading

Written By Ashish Kumar S

|

November 6, 2025

Book a free demo

Make you part first-time-right on machine.

• Cost and Cycle-time optimization
• Program in 15 minutes
• Easy to learn

Book a Demo

CNC threading: G76 Fanuc threading cycle – first depth of cut calculation

CNC threading often fails because of improper depths of cut. Too high depth of cut causes excessive load on the tool and part, high tool wear, and poor part quality. Too low depth of cut causes high cycle time and work hardening. In the G76 Fanuc threading cycle you have to specify the first depth of cut. This is also common to other controllers like Haas and Mitsubishi.

Calculating the first depth of cut involves a simple formula, but is not done on 90 % of shop floors. Most programmers have a thumb rule that has no scientific basis.

Here’s the explanationThe cutting load is proportional to the cross sectional area of material being removed. If the depths of cut are constant, the load increases with each cut. The load in cut 2 is twice that in cut 1, in cut 3 it is 4 times more than in cut 1, in cut 4 it is 6 times more, etc. Disastrous for the tool and the part.

To prevent this, controllers have a constant area cutting logic in the threading cycle. The depth of each successive cut is reduced to keep the cutting area and hence cutting load constant. Unfortunately for the programmer, the G76 Fanuc threading cycle (as well as on Haas and Mitsubishi) requires that you specify the first depth of cut in the threading cycle command. They calculate the remaining depths of cut from this. This involves a small calculation, and most programmers do not do this, ending up getting the thread right after some trial and error that involves rejecting a few parts.

This is how you calculate the first depth of cut – just 3 steps:1. Determine the number of cuts based on the workpiece material, type of thread (Metric, UNI, etc.) and the pitch, from the tool manufacturer’s catalog.2. Use this formula to determine the first depth of cut.E.g., if the thread depth is 1.28 and the number of cuts is 8, the depth of the first cut is 0.45.

3. Use this value in the threading cycle. E.g. on a Fanuc controller you would program this as Q450 in the second line of the G76 cycle (the value is programmed in microns in Fanuc).

Action pointEnsure that this simple method is used for calculating the first thread depth to program threading.ORGet a software like CADEM CAPSturn CNC lathe programming software that automatically determines the number of cuts based on the type and size of thread, and outputs the correct value in the threading cycle in the program.

Author

Ashish Kumar S

cadem Ashish brings strong techno-commercial depth across CNC productivity solutions, CAD/CAM systems, and skill development initiatives. As the face of CADEM’s CNC ecosystem, he drives solution adoption and market growth by aligning advanced manufacturing software with real-world production challenges. A passionate advocate of CNC education in India, he actively engages with customers and students to bridge the gap between industry needs and workforce readiness.

• Share this article

Blogs

Explore Similar

How to Build a Scalable CNC Training System That Reduces Attrition

Snapshot In this article you’ll learn: Why CNC operator attrition is risingRisks in traditional trainingHow virtual CNC training protects machinesHow Read More > You Bought a CAM Software. Now Who Will Run It?

Snapshot Buying CAM software is easy, but running it efficiently depends on who knows how to use it • Many Read More > Constant cutting speed – benefits in CNC lathes

Constant Cutting Speed in CNC lathes – ignorance can be expensive Using Constant Cutting Speed (also called Constant Surface Speed Read More > CNC Milling – 2D, 3D, 5-axis milling

CNC What is 2D, 3D and 5-axis Milling2D milling (also called 2.5 D milling): 1. The tool axis is constant Read More > Tool life definition – what is tool life in CNC machining ?

Tool life definition – it’s not when the tool breaks Tool life definition: Tool life is the duration of actual Read More > 5S in LEAN manufacturing – what is it, and how does it benefit ?

What is 5S in LEAN manufacturing ? 5S in LEAN manufacturing is a method of organizing the workplace to improve Read More >