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Speaking of Precision Blog

Speaking of Precision

Speaking of Precision is a knowledge preservation and thought leadership blog covering the precision machining industry, its materials and services. With over 36 years of hands on experience in steelmaking, manufacturing, quality, and management, Miles Free (Milo) Director of Industry Research and Technology at PMPA helps answer "How?" "With what?" and occasionally "Really?"

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Thread Rolling Thin Walls--CJ Winters

Posted December 07, 2016 10:00 AM by Milo

Guest post by Lib Pietrantoni, CJWinter

Flaking threads and thread damage can be avoided when thread rolling thin walled parts.

Distortion during the thread rolling process can cause

  • Flaking,
  • Non-uniform thread geometry
  • Tearing
  • Collapse of threaded portion of part

These are particularly troublesome issues on thin walled parts.

These can be avoided if you assure that a minimum wall thickness is maintained for the process.

Minimum Wall Thickness is determined by Nominal Thread Diameter and Thread Pitch

Larger nominal thread diameters require thicker minimum wall thickness; so do coarser thread pitches.

The way that you roll the thread can also be a factor.

According to Lib Pietrantoni at CJWinter, specialized pneumatic radial-pinch-type thread rolling machine attachments can apply equalized rolling pressure across the workpiece, ensuring thread concentricity, eliminating side pressure on both the parts and the machine, and allowing precise control of the penetration rate — especially important for thin-walled parts.

You can download the Thread Rolling Reference Chart at CJWinter’s website: reference chart

As a steel mill Quality Metallurgist, I saw my share of complaints that “the steel was flaking- it must be the steel.”

But the lab results never found the flaking anywhere except where the thread had been rolled – it was never on the bars as shipped.

Pay attention to minimum wall thickness when thread rolling!

And don’t forget to pass this handy chart along to the engineer at your customer that is designing the parts that you make.

Thanks to Lib Pietrantoni at PMPA member CJWinter for providing this reference information.


Editor's note: CR4 would like to thank Milo for sharing his blog, which can also be read here.

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Re: Thread Rolling Thin Walls--CJ Winters

12/09/2016 2:03 PM

Why wouldn't you roll threads with the piece mounted on a mandrel? That would eliminate distortion of the tube.

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