When thread rolling screws and fasteners, it’s important to maintain minimum wall thickness.
This can be a challenging task, particularly when designing and manufacturing thin-walled parts, including bolts and screws, that require thread rolling.
If your design includes walls that are thin, thread rolling parts can become problematic during production, as distortion can occur. Distortion not only causes flaking and non-uniform thread geometry on a completed part, but it can also lead to the tearing or collapse of a part’s threaded portion during the thread rolling process.
To prevent the distortion of thread rolled parts — and the various issues caused by distortion — it’s imperative to maintain minimal wall thickness.
How to Determine Your Part’s Minimum Wall Thickness
In most cases, the required minimum wall thickness for a thread rolled part is determined by two factors: nominal thread diameter and thread pitch. Larger nominal thread diameters require thicker minimum wall thickness; coarser thread pitches also require thicker minimum wall thickness.
For example, take a part designed with 32 threads per inch, a rather fine thread count. Using blanks with diameters of as large as 0.5 in., this part would require a minimum wall thickness between .038/.048 in.; for blanks between 0.5 in. and 1 in., the part would require a minimum wall thickness between .048/.060 in.; and for blanks between 1 in. and 2 in., a minimum wall thickness between .072/.090 in. would be required.
By contrast, a coarser thread rolling screw with a specified 12 threads per inch would require more substantial minimum wall thickness. A 0.5 in. or smaller blank would require a minimum wall thickness nearly three times thicker than a 32-thread part, between .102/.128 in.; blanks between 0.5 in. and 1 in. require wall thickness of .128/.160 in.; and blanks between 1 in. and 2 in. would require minimum wall thickness between .192/.240 in.
The Best Attachments for Thin-Walled Parts
As important as it is to keep minimum wall thickness in mind when designing thread rolling parts, this may not be enough to protect your parts from distortion if you do not employ the correct equipment.
While you can use a standard tangential style attachment on your thread rolling machine to produce thin-walled parts, it is not ideal; even if required minimum wall thickness is maintained, tangential equipment can still cause out-of-round conditions, collapses, and tears.
CJWinter produces a range of specialized pneumatic radial-pinch-type thread rolling machine attachments. Our pneumatic radial-pinch attachments 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.
To learn more about CJWinter’s capabilities and the minimum wall thicknesses for thin-walled parts, contact us today. To assist with your next thread rolling project, we invite you to download our free reference chart to help you determine your part’s required minimum wall thickness.