Plain Bushing Bearing Sizing Guide: Key Parameters, Formulas & Examples

VIIPLUS provide The  self-lubricating plain bearings of any size according to your needs. Our engineers are here to help you! Self-lubricating plain bearings can be used in all kinds of applications, including combustion engines, propellor shafts, and more. Reach out to our sales team for pricing and delivery information!

• Wide variety of product options for different application conditions​
• Lubricated for life options available for decreased grease use​
• High corrosion resistance versions available​
• Wide range of sizes
• Standard assortment includes spherical plain bearings, as well as rod ends, bushings, thrust washers and strips
• On request, VIIPLUS can provide also application or industry specific plain bearings

• Selecting bearing size

   

  Having decided on the appropriate bearing type, it is then necessary to determine the requisite bearing size. The bearing size to be used for an application can be initially selected on the basis of its load ratings in relation to the applied loads and the requirements regarding service life and reliability.

   

A plain bushing bearing—also known as a sleeve bearing or journal bearing—is a cylindrical sleeve designed to support a rotating shaft through sliding contact. Its main function is to reduce friction and distribute loads between moving parts.

Proper sizing of a bushing bearing involves defining its inner diameter (ID), outer diameter (OD), length (L), and radial clearance. These dimensions ensure the bearing can handle load, speed, lubrication, and temperature without excessive wear or seizure.

1. Basic Dimensions

Inner Diameter (ID or d)

• Typically matches the nominal shaft diameter.

• Add a small radial clearance to allow smooth operation under thermal expansion and load.

Outer Diameter (OD or D)

• Determined by the housing bore.

• For press-fit installations, the OD should be slightly oversized:

  • 0.001–0.003 in for shafts ≤ 3 in

  • 0.003–0.005 in for larger sizes

• This ensures adequate interference fit with the housing.

Length (L)

• Usually ranges from 0.5 to 2 times the shaft diameter (L/d ratio).

  • Shorter bushings are better for high-speed applications (improved alignment).

  • Longer bushings are ideal for heavy loads (better load distribution).

2. Radial Clearance (c)

• Diametral clearance = 2c

• Rule of thumb:

  $$c=0.001–0.002\times \text{shaft diameter}$$

• Example: For a 50 mm shaft,

  $$c\approx 0.05–0.1\text{ mm}(\text{diametral clearance }0.1–0.2\text{ mm})$$

• Relative clearance (ψ):

  ψ=2cd≈0.001–0.003ψ = frac ≈ 0.001–0.003ψ=d2c​≈0.001–0.003

  Suitable for hydrodynamic lubrication conditions.

3. Load Capacity (Projected Area Method)

The specific pressure (p) on the bearing surface is:

p=Fd×Lp = fracp=d×LF​

Where:

• F = Radial load (N)

• d = Shaft diameter (m)

• L = Bearing length (m)

Keep p below the material limit (e.g., Bronze: 5–10 MPa static, lower for dynamic applications).

L=Fp×dL = fracL=p×dF​

4. PV Factor (Pressure–Velocity Limit)

For dry or self-lubricating bushings, performance is often limited by the PV value:

$$PV=p\times v$$

where

v=π×d×RPM60v = fracv=60π×d×RPM​

Typical limits:

• PTFE-based bearings: 0.35 MPa·m/s

• Bronze bearings: 1–2 MPa·m/s

If PV exceeds the limit, increase the diameter or length to reduce pressure and extend service life.

5. Material Estimation (Circumference & Volume)

To estimate material requirements:

$$\text{Inner circumference}=\pi \times ID$$ $$\text{Outer circumference}=\pi \times OD$$ Wall volume≈π×L×(OD2−ID2)4text ≈ fracWall volume≈4π×L×(OD2−ID2)​

6. Press-Fit Housing Calculations

For accurate press-fit installation:

• Use standard fits such as H7 (housing) and s6 (bushing OD) tolerances.

• Calculate minimum/maximum interference and required bore size using the nominal OD.

• After press-fitting, expect the effective ID reduction to be 70–100% of the interference value.

7. Advanced Hydrodynamic Performance

For lubricated bushings, performance depends on parameters such as:

• Viscosity of lubricant

• Operating speed

• Applied load

The minimum oil film thickness (hₘᵢₙ) must exceed surface roughness:

hmin>1.2×(Ra1+Ra2)h_ > 1.2 × (Ra_1 + Ra_2)hmin​>1.2×(Ra1​+Ra2​)

This ensures stable operation and prevents metal-to-metal contact.

8. Step-by-Step Design Example

Given:

• Shaft diameter, d = 40 mm

• Radial load, F = 5000 N

• Speed = 1000 RPM

• Material = Bronze (max p = 8 MPa, dry PV limit = 1.5 MPa·m/s)

• Oil-lubricated, desired L/d = 1

Step 1: Determine Clearance

$$c=0.001\times 40=0.04\text{ mm}$$

→ Bushing ID ≈ 40.08 mm (diametral clearance 0.08 mm)

Step 2: Shaft Surface Speed

v=π×0.04×100060≈2.1 m/sv = frac ≈ 2.1 textv=60π×0.04×1000​≈2.1 m/s

Step 3: Projected Area and Pressure
Assume L = 40 mm

$$A=0.04\times 0.04=0.0016\text{ m²}$$ p=50000.0016=3.125 MPa<8 MPap = frac = 3.125 text < 8 textp=0.00165000​=3.125 MPa<8 MPa

Step 4: PV Check

$$PV=3.125\times 2.1=6.56\text{ MPacdotpm/s}$$

→ Too high for dry running, but acceptable for oil-lubricated conditions.

Step 5: Select OD and Fit
Choose OD = 50 mm (wall thickness = 5 mm).
Press-fit oversize OD by approximately 0.05 mm.

Step 6: Verify and Adjust
Recheck for heat dissipation, alignment, and compliance with ISO 2795 or manufacturer standards.

9. Recommended Fits and Standards

For precision installations, use tolerance combinations like H7/g6 or H7/f7.
Always consult manufacturer sizing charts for standard dimensions and clearance recommendations.

Conclusion

Accurate sizing of plain bushing bearings is essential for reliable operation, long service life, and optimal friction control. By considering clearance, pressure, PV value, and fit tolerance, engineers can design bushings that perform efficiently under a wide range of speeds, loads, and lubrication conditions.