Threading operation on Lathe Machine

Threading operation:

External threading:

Internal threading:

To produce helical grooves (threads) on a cylindrical or conical surface , threading operation is done using lathe machine with the help of single-point cutting tool. 

Threading operation is  essential for making fasteners, motion converters, and mechanical joints.

Procedur for threading operation on Lathe Machine:

1. Set up the workpiece:

Secure the workpiece firmly in the lathe chuck, workpiece should be properly centered. 

Machine (turning) the outside surface of the workpiece to the correct major diameter for the thread. (as per the specifications)

Cut a chamfer at the end of the workpiece.

2. Set up the tool and angle:

Mount a 60-degree threading tool in the tool post. 

Set the tool's height so it is aligned with the lathe center. 

Use a thread gauge to set the tool's cutting point square to the workpiece. 

For right-hand threads, set the compound rest at 29 degrees to the right of the workpiece. 

3. Set Lathe Speeds and Gears:

Adjust the quick-change gearbox to the required pitch i.e. threads per inch (TPI).

Begin with a slow spindle speed, typically around 100 RPM for beginners. 

4. Position the Tool for the First Cut:

Apply a layout solution (like a layout dye) to the area to be threaded. 

Move the tool carriage so it is near the beginning of the desired thread length. 

Use the cross-feed handle to bring the tool close to the workpiece, stopping when the handle is at the 3 o'clock position. 

Set the cross-feed dial to zero. 

Using only the compound rest, feed the tool into  the workpiece with light touch, then set the compound rest dial to zero. 

5. Perform the First "Scratch Cut":

Turn on the lathe. 

Engage the half-nut (or split-nut) to start the cut, using the thread chasing dial for tracking. 

Apply a very shallow "scratch cut" along the length of the part. 

6. Check the Pitch and Continue Cutting:

At the end of the cut, disengage the half-nut, move the cross-feed to clear the workpiece, and then return the carriage to the starting position. 

Stop the lathe and check the pitch of the scratch mark with a thread pitch gauge to ensure the settings are right. 

If the pitch is correct, begin cutting the thread to depth. 

On each subsequent pass, feed the compound rest in by a small amount (e.g., 0.001- 0.002 inches) and take another cut. 

Continue making cuts, increasing the depth gradually, until you reach the desired thread depth. 

This way threads (external / internal) are done on the workpiece with the help of Lathe Machine.