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Understanding Rolled Threads vs. Cut Threads

Threads are a critical component of screws, bolts, and fasteners used in countless products and structures. The two primary methods of creating threads are rolling, which forms them, and cutting, which machines them. 

This article will compare rolled versus cut threads, analyzing the performance characteristics and advantages to determine the ideal option based on specific application requirements.

What is a rolled thread?

Rolled threads are created by forcibly reshaping a metal rod or wire through a set of heavy rolling dies to form ridge-like threads around the shaft. 

It is an efficient cold-forming process that uses extreme pressure to deform the material without removing metal. The smooth cylindrical rod gets squeezed between threaded dies that imprint the negative ridge shape onto its surface through the displacement of the material. 

This compresses and hardens the threads, resulting in increased strength. Rolled threads retain corrosion resistance when no material gets removed, avoiding waste generation. Because of minimal preparation before threading, this method enables high volumes of continuous production. 

The dimensional accuracy and finishing quality of rolled threads are also good.

What is a cut thread?

Cut threads are produced by cutting away material to form the ridges using various machining methods. Thread-cutting tools like pipe taps dies, lathes, and CNC gear equipment use sharp cutters to slice the profile out of a workpiece rotated through the threads. 

Single-point cutters, chasers, milling cutters, and grinding wheels can create external and internal thread forms through an interrupted machining sequence coordinated to the lead screw pitch. This removes metal chips, producing waste swarf that must be cleared and disposed of. Multiple roughing and finishing passes may be required to meet the final dimensional tolerance.

As material gets sheared during cutting, surface finish and fatigue resistance are reduced versus cold forming techniques unless post-processes like rolling or burnishing are applied.

Advantages of rolled threads:

  • High quality and tensile strength

The blanks, or unthreaded portion, are pushed between two dies pre-formed with the thread shape. After that, they deform the blanks into the desired shape. 

The material becomes work-hardened due to the increased dislocations this cold working process creates in the metal’s crystalline structure. 

Threads created with rolling machines are as much as 30% stronger than cut threads (untreated). However, heat treatment and post-processing of cut threads reduce this difference.

  • Cost benefits

Unlike cut thread machines, thread rolling machines employ a smaller diameter blank. The process generates no waste as it doesn’t remove any material. The feed rate and throughput are also faster (up to ten times than normal single-point thread cutting). These elements enable a lower cost per part because of decreased operating, material, and machining expenses.

  • Reduced fatigue failure

Metal reshaping produces A smooth root radius at the thread’s minor diameter. This makes it possible for the part to be free of cutter marks or tears. If power is concentrated in a single place, these marks may work as a stress riser, increase fatigue failure rates, and shorten the product life cycle.

Advantages of cut threads

  • Fine finish

Compared to rolled threads, components with a cut thread, like stainless steel screws, nuts, and bolts, might appear more organized and polished. Machine threads are, therefore, perfect for applications where aesthetics are preferred. However, this doesn’t mean rolled threads can’t be used there.

  • Lower costs

There are various tooling options available to create a cut thread. Screw-cutting tools are often more affordable and smaller than rolling plates, which are used to create rolled threads. Cut threads are a better choice for small runs of items or non-standard sizes since they can be made using both regular machine tooling and basic hand tooling.

  • Fewer limitations

Tooling used for cut threads allows for more flexibility in terms of thread length and diameter than for rolled threads; in areas where a forming tool cannot function, such as inside bodies or over short distances, cut threads can be used.

Which one is superior?

When deciding between rolled and cut threads, consider their applications and budget. Rolled threads are preferable if the threaded section and the body don’t have to have the same diameter, the necessary dimensions are minimal, and the cost is an issue.

For precise applications requiring precise body and thread diameter, as well as for bolts or screws with large or uncommon sizes, and when cost is less of an issue, cut threads are preferred.

Conclusion

Both rolled and cut threading methods have merits depending on tolerance, cost, and production quantity needs. Analyzing application performance demands and manufacturing constraints enables selecting the ideal thread production option to optimize functionality, economics, and part quality. Choosing the best process results in fasteners that meet strength, longevity, and budget goals.

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