Why does rigidity (or minimal deflection) matter in a linear guide?

If you're machining a part, for instance, you don’t want the part or the tool to shift when the guide is loaded. In other words, if you’re working on a surface, you don’t want that surface to deflect under load. You want it to stay flat – which means everything involved needs to be as stiff as possible.

So what affects the rigidity of a linear guide?

A bunch of things:

• Design: Ball size, number of balls in the load zone, ball raceway geometry, X- or O-arrangement, and how forces are transmitted through the guide.
• Material: Steel quality, heat treatment, and bolt strength class.
• Size: Size of the guide, type of carriage, and chosen preload class.

So what’s a typical deflection in a ball-type linear guide?

A size 25 guide with a standard carriage and 2% preload – probably the most common type used in handling systems – compresses around 8 microns (0.008 mm) when loaded with 200 kg per carriage.

For machining applications, people often go with 8% or even 13% preload, move up a size, or choose roller guides instead – which drastically reduces deflection.

There’s a great video on this with Carry Lindholm from Bosch Rexroth.