# What bearing friction coefficient should I use for actuator sizing?

> Bearing friction is typically the largest single force term in an actuator sizing calculation, and getting the friction coefficient right matters more than any other input. Catalog values by bearing type: Profiled linear rail (recirculating ball) — μ = 0.003 to 0.005 Cam rollers on steel plate — ...

**Last updated:** 2026-03-24

**Source:** https://live-roll2roll.pantheonsite.io/resources/faq/what-bearing-friction-coefficient-should-i-use-actuator-sizing

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## Question

What bearing friction coefficient should I use for actuator sizing?

## Short Answer

Profile linear rail: 0.003-0.005. Cam rollers on steel plate: 0.002-0.005. Plain bushings: 0.07-0.12. Use our calculator for common presets.

## Detailed Answer

Bearing friction is typically the **largest single force term** in an actuator sizing calculation, and getting the friction coefficient right matters more than any other input.

**Catalog values by bearing type:**

- Profiled linear rail (recirculating ball) — μ = 0.003 to 0.005
- Cam rollers on steel plate — μ = 0.002 to 0.005
- Plain bronze bushings — μ = 0.10 to 0.20
- PTFE-lined bushings — μ = 0.04 to 0.10
- Roller bearings (cylindrical) — μ = 0.005 to 0.010

**The critical reality: installed friction is 2 to 5 times catalog values.**

Catalog friction coefficients represent clean, properly lubricated, perfectly aligned bearings under controlled conditions. In a production environment, actual friction is higher due to:

- Contamination (dust, web debris, adhesive residue)
- Inadequate or degraded lubrication
- Rail or bearing misalignment from installation tolerances
- Preload variation from mounting surface flatness
- Side-loading from web tension or mechanical misalignment

The Detailed calculator includes a **kinstall** multiplier (default 2.0 to 3.0) that scales catalog friction to installed conditions. This is the single most important correction factor in the model.

**Best practice: spring-scale pull test.** Attach a calibrated spring scale to the carriage and pull horizontally at a slow, steady rate. The peak reading is your actual installed friction force. This 5-minute test eliminates the largest source of sizing uncertainty and is far more reliable than estimating from catalog values. If you can measure it, measure it.

Use the [actuator sizing calculator](https://r2r.tech/actuator-sizing-calculator) with measured pull-test values in Detailed mode for the most accurate sizing result.

**Category:** Technical

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## About Roll-2-Roll Technologies

Roll-2-Roll Technologies designs and manufactures patented fiber-optic web position sensors and advanced web guiding controllers — the precision measurement and control core of modern roll-to-roll manufacturing. Spun out of Oklahoma State University's Web Handling Research Center and trusted by Fortune 500 medical, battery, and nonwovens manufacturers, our patented sensors work without recalibration at ±0.1mm accuracy up to 760 mpm — typical customer outcomes are 50%+ less downtime and payback under six months. Headquartered in Stillwater, Oklahoma, our team of PhDs, controls engineers, and industry veterans extends the sensor + controller core into complete web guide systems including stepper-motor-based linear actuators (RLA, BLA, LHS).

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