Thomson™ - Round vs. Square

Design your machine and don't assume that any one linear guide is the
right answer. Problems may arise from lack of experience, miscalculation
and, sometimes, the lack of calculation altogether. A common mistake,
for example, is to over design the linear guide solution, needlessly
increasing component costs and installation time.

Understand the variables and methodically review your machine's
functional objectives. Check out our Application Analyzer to request
free, personalized assistance and also gain immediate access to a recent,
detailed white paper on the proper selection of round vs. square rail and
related online resources. You can also follow this Quick Contact link to reach us immediately.

A Round Rail Overview

Thomson invented the world's first anti-friction linear Ball Bushing bearings in 1946. For many years, these round rail linear guides satisfied every linear motion-control requirement. However, as machines necessitated closer tolerances, round rail didn’t fit the bill every time. Today, round rail is most often used in vertical applications with heavy loads.

KEY ADVANTAGE: Able to accommodate torsional misalignment with little increase in stress to bearing components

Pros

Self-aligning design is more forgiving of poor parallelism and variations in rail height.
Can handle moment loads
Available with continuous support or end support (can span gaps)
Excellent smoothness
Low drag
Highly effective wipers & seals
Generally easier and less expensive to install

Cons

Lower maximum accuracy
Less load capacity
Single bearing can't support roll moment

A Square Rail Overview

Square rails have been in use for over 35 years and were initially designed for the machine tool industry, replacing integrated carriages and ways. Because of their streamlined stature, they are often chosen when esthetics are important.

KEY ADVANTAGE: High positioning accuracy — they hold from 0.0002 to 0.001 in. over 10 ft.

Pros

Highest possible accuracy
Higher rigidity
More compact
Higher load-life capacity

Cons

More difficult to install (mounting surfaces must be precise)
Can’t span the gaps a round rail can
Higher preloads increase drag

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	Design your machine and don't assume that any one linear guide is the right answer. Problems may arise from lack of experience, miscalculation and, sometimes, the lack of calculation altogether. A common mistake, for example, is to over design the linear guide solution, needlessly increasing component costs and installation time. Understand the variables and methodically review your machine's functional objectives. Check out our Application Analyzer to request free, personalized assistance and also gain immediate access to a recent, detailed white paper on the proper selection of round vs. square rail and related online resources. You can also follow this Quick Contact link to reach us immediately. A Round Rail Overview Thomson invented the world's first anti-friction linear Ball Bushing bearings in 1946. For many years, these round rail linear guides satisfied every linear motion-control requirement. However, as machines necessitated closer tolerances, round rail didn’t fit the bill every time. Today, round rail is most often used in vertical applications with heavy loads. KEY ADVANTAGE: Able to accommodate torsional misalignment with little increase in stress to bearing components Pros Self-aligning design is more forgiving of poor parallelism and variations in rail height. Can handle moment loads Available with continuous support or end support (can span gaps) Excellent smoothness Low drag Highly effective wipers & seals Generally easier and less expensive to install Cons Lower maximum accuracy Less load capacity Single bearing can't support roll moment A Square Rail Overview Square rails have been in use for over 35 years and were initially designed for the machine tool industry, replacing integrated carriages and ways. Because of their streamlined stature, they are often chosen when esthetics are important. KEY ADVANTAGE: High positioning accuracy — they hold from 0.0002 to 0.001 in. over 10 ft. Pros Highest possible accuracy Higher rigidity More compact Higher load-life capacity Cons More difficult to install (mounting surfaces must be precise) Can’t span the gaps a round rail can Higher preloads increase drag A great way to start a conversation with one of our application engineers is use the Application Analyzer. It asks questions which will help us begin to identify the optimal linear solution for your specific application. You will receive a personal response and immediately receive the option to download a new, detailed white paper on the selection of round vs square rail.