Are Lead Screws for you?
Are Lead Screws For you?
Are you considering using a lead screw in your linear motion application design? If so, here are four things to keep in mind.
Lead Screw Costs
Lead screws are a lower-cost linear motion solution than any other mechanical, pneumatic, or hydraulic product. Precision lead and acme screws are manufactured from special high carbon alloy steels and anti-corrosive stainless steels that lend themselves to precision thread-rolling processes and the demanding applications engineers apply them. Precision thread-rolling is an efficient way to manufacture large volumes of screws. Lead nuts can also be injection molded in high volumes from engineered plastics at reasonable costs. Many manufacturers will require you to pay for tooling to mold nuts and, depending on the volume, will charge a one-time fee, amortize the cost over each part or waive the fee entirely.
Customization – Don’t be afraid to ask for something special
Nearly every aspect of a lead or acme screw can be customized to fit your application. The most straightforward modifications offered are custom lengths of the screw. Screws can be cut to any size +/- 0.005” with the aid of an abrasive saw or cold saw since they are typically in the Rockwell C range of 20-23. The ends of screws can also be easily machined to accommodate a bearing support block, lock nuts, couplings, pulleys, and handwheels.
Most screws follow the 29° acme thread form for screws in “inch” dimensions and the 30° trapezoidal thread form for metric measurements. Hundreds of custom thread forms have been developed to create specific diameter and lead combinations to meet the demands of applications. For example, screws with aggressive or high leads are designed with thread forms that migrate away from the acme screw and trapezoidal screw standards.
Manufacturing a custom screw requires a set of thread rolling dies that are precision ground from high-performance tool steels that can withstand pressures as high as 200,000 lbs. for most screws. Below is an image of a set of thread rolling dies for Helix precision screws.
Once thread rolling dies have been manufactured, the next step is the precision thread-rolling process. Lead screws are commonly manufactured at 12-foot lengths and then cut to specific lengths before machining the ends. Longer and shorter screws can easily be manufactured.
Lead nuts can also be manufactured in any shape, size, and material. Common materials include bronze, Delrin, PEEK, Acetal, and custom blends incorporating carbon fibers, PTFE, silicone, and glass. These materials can either be machined or molded depending on the design and volumes. Most lead nut manufacturers will create a custom nut design for you and deliver a rapid-prototyped part in 24 hours.
Suppose you’re looking for opportunities to reduce part counts on bills of material. In that case, the design of a lead screw nut can easily incorporate different machine components, which lends itself well to molding the nuts for higher volume OEM applications.
Matching the duty cycle of your application to the correct lead screw is essential. Lead screws are typically used for a low-duty cycle or intermittent applications. Still, the development of specialized PTFE coatings on screws, custom thread forms, and PTFE and Silicone impregnated nut materials are often used in higher duty cycles and precise applications like fluid pumps, medical equipment, security cameras, and coffee machines. Most lead screw manufacturers will assist you in selecting a lead screw to match the duty cycle of your application.
If your machine design demands clean components without oils and greases for lubrication, a lead screw is an excellent solution for creating precise linear motion. Screws can be manufactured from 300 and 400 series stainless steels that are anti-corrosive and coated with an array of PTFE coatings that make them perfect for medical diagnostic equipment, robotic applications, and semiconductor manufacturing applications.
If you need a solution for a linear motion application that is low duty cycle, needs to be clean and low cost, and needs to be customized - take a look at Helix lead screws.