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WOODEX Oil-

impregnated Wood

Bearings: Design

& Engineering

Information

Choose a topic or scroll down for all information.

Physical Properties

Speed vs. Load - P/V Factor

Material Max P/V

Wall Thickness

Shaft Diameter & Recommended Wall Thickness

Installed Bearing Clearances

Press Fits

Close-In

Grain Direction

Lubrication

Installation

Application Information

Physical Properties

Lubricant content by weight 41-47%

Tensile Strength 1150 psi

Compression permanent deformation (psi, for .005" set) 7500

Specific Gravity 1.3

Coefficient of thermal expansion per F 4.3 x 10^-6

Temperature range -50 - 160F

Coefficient of friction .07 to .115

Weight per cubic inch, lbs. .039

Wear rate factor

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Max V 2,000 SFM

Speed vs. Load - P/V Factor

All bearings have a P/V rating (Pressure/Velocity) based on empirical

testing. The rating is a mathematical expression of Pressure (PIA = pounds

per inch of projected area) times Velocity (SFM = surface feet per minute).

The expressed P/V value of a material is the maximum load-speed that a

bearing can withstand. This value is further refined by the maximum PIA

and SFM that the material can withstand regardless of the total P/V value.

The recommended P/V factor for WOODEX is 12,000, with a maximum

PIA and SFM of 2,000 each.

As a comparison, the following are operating characteristics of a variety of

bearing materials:

Material Max P/V Max P Max V

Inj. Molded Nylon 101 3,000 380 475

Delrin 3,000 1,000 100

UHMW-PE 4,000 1,200 50WOODEX 12,000 2,000 2,000

Babbitt (10% tin) 18,000 1,300 1,400

Oilite Bronze 50,000 2,000 1,200

Cast Bronze SAE 660 75,000 3,000 750

WOODEX is unusual in that it has the capability to handle both high

speeds and loads, a quality that enhances its flexibility. As an example, in a

dry, ambient condition a 2" long WOODEX bearing supporting a 1" shaftcan support a shaft load of up to 1,800 pounds, while the shaft is rotating

at 50 rpm. Conversely, the bearing can tolerate a shaft RPM of up to 1,800,

while the shaft load is 50 pounds.

To calculate the P/V for any given application, use the following formulas:

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PIA and SFM must each equal 2,000 or less. Multiply PIA times SFM: the

product (P/V) must be 12,000 or less. If true for all three values, WOODEX

may be right for your application.

OTE: Add appropriate safety factors to both load and speed before

calculating.)

Wall Thickness

It is important that the wall thickness of the bearing meet minimum

standards. Proper wall thickness will guarantee a sufficient supply of

lubricant to last the life of the bearing. Shaft size can rarely be reduced, but

housing size may be increased to satisfy this requirement.

Shaft Diameter Recommended Wall Thickness*

up to 1/2" 1/16" to 1/8"

1/2" to 1" 1/8" to 3/16"

1" to 1 1/2" 3/16" to 5/16"

1 1/2" to 2" 5/16" to 3/8"

2" to 2 1/2" 3/8" to 1/2"

2 1/2" to 4" 1/2" to 5/8"

* Thinner bearing wall may produce reasonable service life under certain

conditions.

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Clearances

An oil-lubricated bearing must have sufficient clearance to allow the

lubricant to penetrate and form a lubricating film. Insufficient clearance

will inhibit this lubricating film and excessive clearance will allow

excessive movement between parts. Either condition will result in

premature bearing failure. The inside diameters of all WOODEX bearings

are machined oversize to provide the required clearance. Designs that

require tighter tolerances can be met by supplying bearings without built-

in clearance and calling for reaming at installation. Reaming will not

restruct the self-metering lubrication qualities of the bearing.

Installed BearingClearances

Shaft Diameter Operating Condition Roll-end OperatingCondition

Dry Wet Dry Wet

up to 1/2" .002"-.010" .020"-.028" .015"-.024" .030"-.035"

1/2" to 1" .004"-.016" .024"-.032" .024"-.028" .035"-.042"

1" to 1 1/2" .007"-.019" .038"-.046" .024"-.030" .038"-.050"

1 1/2" to 3" .010"-.025" .045"-.060"

3" & up .015"-.031" .050"-.066"

Press FitsA WOODEX bearing remains stationary in its housing because it has been

furnished with an oversized outside diameter to ensure firm retention.

Sleeve, flange and roll-end bearings are all machined to include this press

fit. Oil impregnated maple bearings have greater press fit dimensions than

metal, since they are much more compressible.

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Close-In

The compressibility of oil-impregnated rock maple means that

approximately 70% of the press fit on a WOODEX bearing will be reflected

in close-in of the inside diameter. WOODEX bearings are normally

furnished with an oversized inside diameter. This provides a correct

running clearance once the bearing has been pressed in place and the

close-in effected.

Press Fit - Close-In

Nominal O.D. Press Fits Close-In Factor

up to 1/2" .003"-.006" .003"

1/2" to 1 1/2" .004"-.008" .004"

1 1/2" to 3" .005"-.010" .005"

3" & up .006"-.012" .006"

Grain Direction

In a lubricated bearing, the oil must be delivered to the load carrying area

of the interface. In order to do this, a wood bearing must have its bore at

right angles to the grain of the wood. Aligned in this cross-grain fashion,

the cell structure meters the lubricant to the interface.

Lubrication

WOODEX bearings self-lubricate in three modes:

boundary lubrication

full film (hydrodynamic) lubrication

mixed film lubrication

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These modes indicate the effectiveness of bearing lubrication in reducing

friction.

Under full-film lubrication, the shaft is completely separated from contact

with the bearing by a thick film of lubricant. Without shaft to bearing

contact, bearing service life is nearly infinite. This condition is rarely - if

ever - achieved with a wood plane bearing.

Boundary lubrication permits bearing-shaft contact in the presence of an

extremely thin lubricating film. Bearing wear is proportional to load and

speed.

Mixed film lubrication combines both other modes. Pools of self-

pressurized lubricant accept part of the load while very thin films take the

rest.

WOODEX bearings are charged with a lifetime lubricant supply. Outside

lubricants should not be used, as they will impair the natural action of the

WOODEX lubricant.

Installation

An arbor press should be used to press a WOODEX bearing into place. A

slight chamfer is furnished on one end of the bearing as an aid in starting

the fit into the housing. The inside of the housing also should be slightly

rounded or relieved to make sure there is no burr on the edge of the

housing to cut the bearing as it is pressed into place.

Application Information

When inquiring about custom WOODEX bearings, please be sure to

include the following information:

Nominal Housing Dimensions

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Bearing Length

Shaft diameter

Shaft Speed

Shaft Load

Temperature, and

Operating Condition (wet, dry or partially-wetted)