we can host it on our YT site if you want mitch send me the video and I’ll get it posted.
Machineshop 101 wire gauge method.
The Three-Wire Method is a widely accepted and standardized method for measuring the pitch diameter of threaded parts. It provides a high degree of accuracy by measuring the diameter across three evenly spaced wires of a known diameter, which are placed in the thread grooves.
Here’s a step-by-step guide to checking pitch diameters using the Three-Wire Method:
1. Understand the Concept:
- Pitch Diameter: It’s the diameter of an imaginary cylinder where the width of the groove and the width of the thread are equal.
- Three-Wire Method: Uses the known diameter of wires and the measurement over these wires to compute the pitch diameter.
2. Gather Necessary Tools:
- Micrometer: To measure over the wires.
- Set of Thread Measuring Wires: These come in various sizes; you need to select the correct diameter based on the thread pitch you’re measuring.
- Thread Pitch Gauge: To determine the thread’s pitch.
- Thread Tables or Calculator: To find the constant values for the wire size and the thread pitch being measured.
3. Procedure:
- Determine the Thread Pitch: Using the thread pitch gauge, identify the pitch of the thread you wish to measure.
- Select the Correct Wires: Based on the thread pitch, consult a thread-wire chart to determine the appropriate wire diameter to use.
- Place the Wires: Put one wire in one groove and the other two in two grooves on the opposite side, spacing them so they are evenly distributed around the part.
- Measure Over the Wires: Use the micrometer to measure over the top of the three wires, ensuring you are getting a measurement that’s perpendicular to the axis of the threaded part.
- Calculate the Pitch Diameter:
- Use the formula: Pitch Diameter=Measurement Over Wires−(Constant from table based on thread pitch and wire size)Pitch Diameter=Measurement Over Wires−(Constant from table based on thread pitch and wire size)
- The constant is typically found in machinery’s handbooks or thread measurement tables.
4. Tips:
- Ensure the wires and threads are clean.
- Make sure the micrometer’s anvil and spindle are parallel to the three wires when taking measurements.
- For better accuracy, take multiple measurements and average them.
5. Advantages of the Three-Wire Method:
- Highly accurate.
- Standardized, so it’s accepted across many industries.
- Allows direct measurement of pitch diameter, which can be challenging to measure by other methods.
By mastering the Three-Wire Method, you can achieve precise and reliable measurements of threaded parts, which is essential in many machining and manufacturing applications.
Wire size for 20 TPI:
More from machinist pocket companion:
Incase you want to measure the threads as properly as possible.
I don’t own any wire sets, so never used the three-wire method. Although I can see how it could be quite accurate I got quite a laugh out of imagining myself trying to hold a threaded part, three wires and a micrometer or caliper while adjusting the caliper to take the measurement. Still laughing when imagining the threaded part being held in a lathe chuck.
I think that either this is a theoretical method that nobody has ever actually used or else is an expert machinist’s secret process that is passed along from one old-timer to a worthy apprentice when they become a journeyman.
YouTube videos show several methods for holding the wires with and without aids.
Everything is easy when you are watching someone else doing it. Even Rhino.