Both linear shafts and linear rails are used for linear motion, but there are some key differences between them:

Linear shafts:

• Simple design: A round shaft made of steel, stainless steel, or hardened chrome.
• Lower cost: Generally cheaper than linear rails.
• Easy to install: Can be supported by bearings or bushings.
• Less accurate: Can bend or deflect under load, leading to less precise motion.
• Lower load capacity: Not suitable for high-load applications.
• Higher friction: Requires more lubrication than linear rails.
• Limited self-alignment: Can twist or rotate under load, requiring additional components to prevent it.

Linear rails:

• More complex design: Consists of a hardened steel rail with rolling elements like ball bearings or rollers.
• Higher cost: More expensive than linear shafts.
• More difficult to install: Requires precise alignment and mounting.
• More accurate: Offers more precise and consistent motion due to its rigid design.
• Higher load capacity: Can handle heavier loads than linear shafts.
• Lower friction: Requires less lubrication than linear shafts.
• Self-aligning: Some types of linear rails can self-align, compensating for minor misalignment.

Key differences:

Choosing between linear shafts and linear rails:

The best choice for your application will depend on several factors, including:

• Required level of accuracy and precision
• Expected load
• Budget
• Complexity of installation
• Need for self-alignment

Here are some general guidelines:

• Use linear shafts for:
  • Low-cost applications
  • Simple designs
  • Light loads
  • Non-critical applications where high accuracy is not required
• Use linear rails for:
  • High-precision applications
  • Heavy loads
  • Complex designs
  • Applications requiring self-alignment

Here are some additional resources that you may find helpful:

• Linear rails vs. linear rods – which are better? https://www.matara.com/technical-articles/linear-rail-faqs/
• Round shaft or profiled rail for linear motion? How to choose https://www.linearmotiontips.com/round-shaft-or-profiled-rail-how-to-choose/
• Linear Ways vs Linear Rails vs Linear Rods (Im searched out and still lost) https://www.cnczone.com/forums/linear-and-rotary-motion/167612-cnc.html