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There are a bevy of factors that dictate the performance of a lead screw, to include how it is mounted, as we covered in our last article. However, we believe that the most important factor is the pairing of the lead screw with the lead screw nut.
There are a bevy of factors that dictate the performance of a lead screw, to include how it is mounted, as we covered in our last article. However, we believe that the most important factor is the pairing of the lead screw with the lead screw nut.
It may sound like we're stating the obvious but we don't think so. Due to the many advancements in nut design and material variety it's not such a straightforward decision these days. It’s common for some to overlook the impact of the nut after they've selected the lead screw for a particular application, but as many motion control applications are becoming more and more sophisticated - notably those in lab automation and medical equipment - the proper pairing of the lead screw and nut are becoming a paramount design decision. A single lead screw may have dozens of nut options and even those may not suit your particular application.
Yes, there are a variety of standard nuts available, which offer the perfect choice for most applications (just as standard lead screws are suitable for many applications). But then there's also the option of a custom-engineered lead screw nut to meet the needs of more advanced and sophisticated applications - applications where there's little room for error or applications where the parameters of the overall design require something “outside of the box”. How do you know whether or not a standard nut will do the trick or if a custom nut is in your application's best interest?
Here's a look at some of the design variables that you might want to consider during the nut-selection process to help with your decision:
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Temperature constraints: Does the application need to operate within a certain temperature range? Certain custom materials that we use for our custom nuts perform well in high and/or low temperatures.
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Chemical compatibility: How important is corrosion resistance? Will materials be impacted in a negative way by the environment the application will be operating in? Needless to say, certain materials are more corrosion resistant than others.
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Wear: How long does the nut need to last in the particular application? Nuts can be custom engineered to last for extended periods of time.
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Matching leads: Do all leads in the application have to remain consistent?
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Lubricants: It's common for a lead screw nut to require some sort of lubrication, but does your selection require a special type of lubrication? What about self-lubricated nuts?
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Backlash: Do you need to worry about lash? Should you be considering an anti-backlash assembly?
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Flange: Does a flanged nut, or a nut with no flange work better in your application? Can you eliminate another component or simplify the design by choosing a flanged nut?
- Cost: It's true that a custom design may cost a little more than a standard nut initially but that is not always the case. Perhaps it can even reduce the overall cost and complexity by incorporating design elements of other components, thereby eliminating them and their potential failure points. A custom nut may also contribute to lower maintenance cost and failure reduction. How heavily do these factors weigh in the design?
After you've carefully analyzed all of the design variables above, it's time to stack up standard nuts with custom nuts. Custom nuts don't necessarily have to be advanced or highly complex, in some cases they can be as simple as a dimensional change or use a special type of material or a custom mounting hole pattern. Thread options and specific manufacturing techniques may also be used to fabricate custom nuts. Custom nuts provide engineers with greater design flexibility and thereby allow them to design without being constrained by the parameters of the lead screw assembly.
Lead screw nuts can be created in a variety of advanced materials these days. At Helix, we're able to create custom nut configurations in many types of plastics, including PEEK, polyester, acetal, Torlon, Vespel, PVDF, UHMW and Ertalyte, to name a few. Many of the aforementioned nuts, such as those manufactured from Torlon, Vespel and PEEK are those that are ideal for applications that need to operate in high temperatures. Aside from plastic materials, nuts can also be fabricated from materials such as carbon fiber, graphite, glass fibers and even silicone.
As we mentioned earlier, lab automation and medical device design and manufacture are two areas that are playing a big role in driving lead screw development and innovation. This is primarily due to the requirement for increased precision and demands for a smaller footprint. With that being said, the resulting lead screw assemblies necessary to drive these applications have produced some impressive lead screw nut innovations. Custom nuts have already come a long way - and their design advancements are likely to continue.
As we mentioned earlier, lab automation and medical device design and manufacture are two areas that are playing a big role in driving lead screw development and innovation. This is primarily due to the requirement for increased precision and demands for a smaller footprint. With that being said, the resulting lead screw assemblies necessary to drive these applications have produced some impressive lead screw nut innovations. Custom nuts have already come a long way - and their design advancements are likely to continue.