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 to the demanding applications where engineers apply them.
Are Lead Screws For you?
Are you considering using a lead screw in your design? If so, here are four things to keep in mind.
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 to the demanding applications where 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 simplest modifications offered are custom lengths of the screw.Screws can be cut to any length +/- 0.005” with the aid of an abrasive saw or a 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 hand wheels.
Most screws follow the 29° acme thread form for screws in “inch” dimensions and the 30° trapezoidal thread from for metric dimensions. Hundreds of custom thread forms have been developed to create specific diameter and lead combinations to meet the demands of an applications. For example, screws that have 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 a set of thread rolling dies has been manufactured, the next step is the precision thread-rolling process. Lead screws are most commonly manufactured 12 foot lengths and then cut to specific lengths prior to 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 that can incorporate 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.
If you’re looking for opportunities to reduce part counts on bills of material, the design of a lead screw nut can incorporate different components of a machine easily, 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 important. Lead screws are typically used for low duty cycle or intermittent applications but the development of specialized PTFE coatings on screws, custom thread forms and PTFE and Silicone impregnated nut materials, they are often used in higher duty cycle 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 a great solution for creating precise linear motion. A 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 cusomized - take a look at Helix lead screws.