A Quick Guide to Linear Shafts

A linear shaft is a metal rod that moves large objects or assemblies on a linear plane. These precision parts are used in a variety of industries, and they provide smooth and precise movement. You’ll find linear shafts in things like MRI machines, vehicle seats that move back and forth, and printing and packaging machines. The linear shaft is the part that provides support and keeps everything in the proper place as they move.

There are a few different types of linear shafts. Most of these are made with hard metals and have the strength required to support 100s or 1,000s of pounds.

This guide to linear shafts will give you some info about how the shafts are manufactured, the various types, and their use cases.

What is a linear shaft?

A linear shaft is a metal rod that supports linear motion (moving in a straight line). Usually this is a sliding or gliding motion. The shaft is mounted onto the application and doesn’t move, but rather supports the parts and components that are moving. In the case of powered mechanisms, the shaft works with an actuator, support rails, or bushings and ball bearings for manual movements.

The shaft is the piece that’s usually bearing most of the weight, so they’re manufactured with durable metals that can withstand the weight and resistant to wear over time from the other parts sliding back and forth.

Types of linear shafts

The general shape of the linear shaft is the same—a smooth metal rod. There are slight variations, depending on the specific use of the rod.

Many linear rods are solid metal to provide the necessary tensile strength. They can be hollow or have a key slot that allows wiring or liquid to move through them.

Other features are added to the ends of the rods. Inner and outer threading, stepped and chamfered ends, or holes can be added to the ends for mounting purposes.

Common applications

Linear shafts are used in just about anything that moves or slides back and forth with precision. You won’t find these shafts in your sliding kitchen drawers, because precise movement isn’t required.

Here are a few of the real-world applications:

Aerospace industry: Linear shafts are used to move seats and to slide out stairs and ramps.

Automotive industry: Linear shafts are used for electric seat adjustment.

Medical industry: Linear shafts are used for many different machines like MRI machines, scan machines, operating tables, and more.

Manufacturing industry: Linear shafts are used for printers and packaging machines, and sliding tables.

Linear shafts can only be mounted and supported from each end, because the other parts are moving up and down the shaft. In cases where longer distances are required, and more weight is being moved, a rail system is preferred. The rail system can be supported at multiple points without interrupting the movement because the moving parts only use the top part of the rail.

How are shafts machined?

To provide smooth back and forth movements, the shafts need to be machined with precision, and have a smooth surface finish. The most common machining method is CNC turning or lathe machine.

These machines hold the raw bar stock in a spindle and rotate it at high speeds. A cutting tool works to remove the material to the specified part design. CNC turning machines are the most efficient type of machine for making cylindrical parts with precise measurements like linear shafts.

In most cases, the milling machine can form all of the part features at the same time, so no secondary machining is required. Depending on the surface roughness requirements, the shafts might be polished after machining to improve the smoothness.

Materials and coatings

The primary function of linear shafts is to support weight and provide smooth movements.

The most common materials used are stainless steel alloys. Stainless steel provides great strength and resistance to wear and corrosion. 304, 316, and 316L stainless steel alloys are the most commonly used because they provide excellent corrosion resistance. 316 and 316L are preferred for applications in food processing, semiconductor, and medical industries. 440 stainless steel is also great for high pressure applications.

In cases where lower tensile strength is needed, aluminum alloys are used. Aluminum is much lighter, less expensive, and still has good corrosion resistance. Most aluminum shafts are anodized to increase durability.

When rust and corrosion is less of a concern, carbon steel is used. This is much less expensive and offers similar tensile strength as stainless steel. Carbon steel can also be plated or heat treated to improve corrosion resistance.

Order custom linear shafts

Spex offers a large selection of custom precision machined parts for whatever your project needs. We are an ISO 9001:2015 certified company, and our team specializes in precision machining and supply chain efficiency. Our machined components are available in an array of different materials and finishes and are manufactured to meet all the highest quantity needs.

Reach out to our team to get a quote for your next project.