How to Use a Lathe to Thread a Gauge

Threading a gauge on a CNC lathe can help with accuracy.

Gauges are used by machinists to check the threads of parts that are made on a lathe. Like parts with threads, gauges must also be made on a precision machine such as a computer numerical control (CNC) lathe. Gauges must have very tight tolerances, which are deviations from specified sizes, and must be made accurately so that production parts are measured properly. Carefully setting up the lathe and checking the gauge before removal allow for this accuracy.

Things You'll Need

• Allen wrench
• Chuck jaws
• Carbide insert cutter
• Grooving insert cutter
• Threading insert cutter
• Thread gauge

Instructions

1. Set up the chuck to hold the material you will thread on the lathe. Use chuck jaws whose radius matches the radius of the material. Remove the chuck jaws that are in the chuck by loosening the two screws on each jaw and sliding the jaws out. Remove the retention blocks, place them on the new jaws and slide them into place. Tighten the screws on each jaw after lining them up to be equidistant to the center of the chuck.

2. Place an outside diameter carbide insert tool, grooving tool and threading tool in the tool turret. Lower the probe to teach the tools. Manually bring each tool tip up to the probe, enter teaching mode on the CNC control and wait for the beep. Teaching each tool tip allows the control to know where the tip is to machine the part accurately.

3. Program the machine to cut the threads for the gauge. Program the outside diameter to bring the material to the correct maximum diameter for the gauge. Set the grooving tool location and depth for the relief on the back side of the threads and program the threading passes, both roughing and finishing. Use the correct tool number for each so that the control knows which tool to use for each operation.

4. Set the Z zero for the part, which is the starting point for the program. Bring any of the tools to the end of the raw material and reset the Z on the control. An accurate starting point is essential for proper machining, as the control will use this spot to start the operations placed in the program.

5. Run the program by placing the lathe in "Auto" mode. Press cycle start and carefully watch the approach of the first tool, which will be the outside diameter cutter. Continue to watch each tool's approach to make sure that the program is correct. Examine the threads after the program has been completed to ensure that the cuts look correct before using a thread gauge to check them.

Tips & Warnings

• Check the gauge thread before removing it from the chuck. That way, you can rerun the program if the threads are too big.

References

• Dave Hylands: CNC Threading