Plain Linear Bearings | FAQs

Plain Linear Bearings | FAQs

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Why would I use a Simplicity plain bearing instead of the linear ball bearing I’ve always used?

There are multiple advantages that the Simplicity linear bearing with a FrelonGold liner has over linear ball bearings, but there are two that stand out the most. First, they are self-lubricating or do not require additional grease and oil to be added to operate properly. Linear ball bearings require grease to be used. Secondly, the Simplicity plain bearings handle contamination extremely well by creating a natural seal on the shaft and pushing the dirt, dust, chips, and other contaminants to the end of the stroke. Linear ball bearings must have added seals that often allow particulate to slip past and into the raceways where it will catch in between the balls and stop them from rotating which leads to failure.

Why would I use a linear ball bearing instead of a plain bearing?

There are two main reasons you might want to consider a linear ball bearing over a plain bearing. First would be that they have a low coefficient of friction meaning the balls will roll more freely than the surface of a plain bearing will slide. This will result in the ball bearing being better suited to higher speed applications. Second would be in places where a preload is required. In other words, the balls can be slightly “squeezed” by the casing around the bearing and the “play” between the bearing and shaft is removed. These bearings might be used where more precision may be needed.

Do all plain Bearings have a removable plastic insert?

The short answer is no. The term “plain bearing” applies to any bearing that does not have rolling elements, but instead is made up of a solid surface that slides along the shaft or raceway. The bearing surface could be plastic, bronze, or other polymer-based materials. PBC Linear Frelon and FrelonGold were specifically developed through intensive tribological testing for linear motion applications. Also, note that these materials from PBC Linear are not inserts, but rather the material is bonded permanently into place with a structural adhesive similar to how airplane wings are bonded together creating a one-piece bearing.

How do you mount linear bearings in place?

The easiest way is to purchase them already mounted in standard pillow blocks where they are fixed in place with retaining rings and/or a pin. If standard pillow blocks are not an option, you could create your own housing and retain the bearing at the ends with retaining rings or bore the housing to specification and then press fit the bearing. Instructions for bearing installation can be found in the RST catalog here: Catalog

What linear bearings will stand up to harsh chemicals?

In general, stainless steel jacketed bearings will hold up the best in harsh chemicals, and many polymer-based materials can be chemically inert. It is always best to check with a specific manufacturer on chemical compatibility. PBC Linear bearings Chemical Reaction Chart can be found here: Chart

What are the grooves on the outside of a linear bearing for?

The smaller grooves toward the ends of a linear bearing are designed for retaining rings that can hold the bearing in a housing. The larger inner grooves on Simplicity linear bearings are for O-rings that will help cushion slight movements when used in a self-aligning pillow block.

What happens when I put a cantilevered load on a linear bearing?

Both plain bearings and linear ball bearings will work in cantilevered load applications, but keep in mind there are consequences for each. With a plain bearing, the load must stay within the 2:1 ratio or the bearings will bind causing stick-slip or possibly locking up the motion. Linear ball bearings may continue to operate beyond the 2:1 ratio, but keep in mind that the balls will be causing increased point pressure on the shaft resulting in galling and severely shortened life. You can learn more about the 2:1 ratio here: Video

Are not all linear bearings imported into the USA today?

No, PBC Linear is committed to manufacturing in the USA and has a 50-acre campus with over 250,000 square feet of production space where approximately 100 machines keep their spindles turning to produce millions of bearings each year.

Can I use a linear bearing in a pivoting or rotary application?

You cannot use a linear ball bearing in a pivoting or rotating motion due to the arrangement of the balls in the raceways. However, because a plain bearing like Simplicity has a solid gliding surface for the bearing, it can move in any or multiple directions at the same time.

What sort of life expectancy can I anticipate from a PBC Linear plain bearing?

There is no known formula for accurately and reliably predicting the life of a plain bearing because there are too many dependent variables.

  • Many of the factors are dependent upon the coefficient of friction, which can change and is difficult to exactly determine. Page 15 of the Round Shaft Technology catalog describes some of the application parameters and factors affecting wear life.
  • A “life calculator” provides estimates, but infinite variables result in too many possibilities. In addition, the failure mode depends upon the user’s definition – is life defined as complete wear out of the liner, or increased running clearance due to wear that results in too much play?
  • Testing under the specific application conditions is the best method to determine life. An online resource comparing PBC Linear to a competitor under specific conditions can be easily viewed here: White Paper
  • PBC Linear has a wear rate vs. life expectancy example for linear plain bearings detailed on our online Catalog.
Are end stops available for support rail assemblies?
PBC Linear does not offer end stops for any Round Shaft Technology.
Are Simplicity bearings FDA approved?
Standard Simplicity bearings with the Frelon liner and anodized aluminum housing are not considered FDA “approved.” However, they are FDA compliant when installed properly. If the food item is not yet packaged, Simplicity bearings are compliant as long as there is no contact with the food item. If the bearings are located over the unpackaged food item, there should be some sort of shield between the bearings and the food. If the bearings are located away to the side or below the unpackaged food, no shielding is necessary. If the food item is already packaged, there is no issue. The Frelon W liner is suitable for food contact.
Can I use Simplicity bearings on cold rolled steel shafting?
Simplicity Frelon lined bearings are designed to run on shafting with a surface finish of 8-12 RMS for best performance, but can accept up to 16 RMS. Rougher shafting can be used, but both bearing and shafting will wear at accelerated rates and binding may occur. Likewise, shafting that is smoother than 8 RMS will result in accelerated wear because the Frelon will not be able to accomplish the transfer process.
Can you interchange Simplicity Plain Bearings to other manufacturer's (or part number) bearings?
Simplicity linear plain bearings are made to industry standards and can offer a dimensional interchange to most other manufacturers’ linear bearings. This comparison applies primarily to ID, OD, and length. Differences such as distance between snap ring grooves, materials, or load ratings should be addressed according to the customer's specific application. It is the customer's responsibility to verify proper fit for their application.
I need a system with low friction. Which PBC product offers the lowest coefficient of friction?
A rolling element, such as ball bearing or roller, will offer a lower coefficient of friction than a sliding element (plain bearing).  There are many factors to consider in addition to coefficient of friction, so it’s important for PBC to understand all aspects of the application to offer proper guidance.
How thick is the Frelon liner?
The thickness has been optimized to provide long life for almost all applications.  The exact thickness is confidential.
I require a flange mount larger than 1" diameter, what are my options?
For an off-the-shelf item, the SDS, DDS, and PAC die sets offer options for a flange mount in diameters up to 2".
What is the average life of a bearing?
Basic life or L-10 as defined by the International Organization for Standardization (ISO) and American Bearing Manufacturers Association (ABMA), is the life that 90% of a sufficiently large group of apparently identical bearings can be expected to reach or exceed. The median or average life, sometimes called Mean Time Between Failure (MTBF), is about five times the calculated basic rating life. PBC Linear has a broad range of linear motion solutions and a detailed approach to calculating life.
Is there a brake for Simplicity pillow blocks?
PBC does not offer a brake for the Simplicity pillow blocks.
The bearing plugs on my square bearing seems loose, can I use Loctite?
You may use removable thread locker to hold the adjustable bearing plugs in position on the square bearing.
Why do the metric pillow block housings list one bolt size in the catalog, but the CAD model measures differently?
Referencing the catalog, threaded portion that extends from the bottom surface of the pillow block and refers to the thread listed in the table. This is intended for a fastener coming from the bottom and threading into the block from the mounting framework.

The counter bored part of the mounting hole originates from the top, or open side of the block, and this mounting direction is intended for a smaller diameter fastener installed from this side of the pillow block. This ensures the fastener has enough clearance to go all the way thru the threaded section of the block without interference, and thread into the mounting framework.
Do the seals add to the overall length of Simplicity Bearings?
Seals are installed into grooves machined into the ID of the bearing, therefore the overall length of the bearing is not affected.
What do the terms accuracy and repeatability mean?
  • Accuracy refers to the ability to achieve a commanded position
  • Repeatability refers to the ability to go to any given spot in a consistent grouping
For more information please see our blog: Factors Which Affect Accuracy & Repeatability
What are the press fit/slip fit dimensions for Simplicity bearings?
PBC Linear recommends use of the compensated ID bearings for press fit applications. Inch (PS & PSF) and metric (PSM & PSFM) sleeve bearings have fit info in the dimensional tables specific to each particular series in the Round Shaft Technology catalog.
What are the velocity and acceleration limits of a Simplicity Plain Bearing product?
For a Simplicity Plain Bearing product the velocity and acceleration is rated in terms of speed or “PV” — this is a calculated value based on “P”resure (or load) multiplied by “V”elocity (speed) to determine the acceptable speed of the bearing in a given application.

Please see our Round Shaft Technology catalog for specific technical specifications.
What does the 2:1 ratio for cantilevered loads mean?
In general terms, if the load or driving force is located (1) off centerline of the bearing(s), or (2) in the line of movement but some distance from the bearings, this distance must not be greater than twice the distance of bearing separation on the same shaft.  Or, if only one bearing is used, the distance must not be greater than twice the length of the bearing itself.  Binding will occur if the 2:1 ratio is exceeded.  Besides proper bearing separation, another method of preventing binding is to use a counterbalance. Please see our blog Cantilevered Loads and the 2:1 Ratio for more detail
What effect will “X” chemical have on Simplicity bearings?
Frelon J has almost universal chemical inertness. Only molten sodium and fluorine at elevated temperatures and pressures show any signs of attack. FrelonGOLD has fillers that can be attacked by certain harsh chemicals. The standard anodized aluminum shell has good chemical resistance in most industrial applications. The optional 316 stainless steel shell has excellent chemical and corrosion resistance in most industrial applications. Check the chemical reaction chart for specific chemicals. The information provided is for reference only – the user must test specific applications.
What is L-10 life?
The L-10 (L10) life is the number of hours in service that 90% of bearings will survive. Or, conversely, 10% of bearings will have failed in the L-10 number of service hours. L10 life is the preferred term in specifying bearing life and is defined by the American Bearing Manufacturers Association (ABMA). PBC Linear provides load ratings on all our products in order to calculate L10.
What is the coefficient of friction (COF) for Simplicity bearings?
The coefficient of friction for filled Teflon can range from .125 to .4 depending on the fillers used.  FrelonGOLD has an average COF of .125, while FrelonJ has an average COF of .12
What is the difference between the 2-sided and 4-sided square bearings?
The 2-sided bearing has only 2 sides with adjustable plugs, the other 2 sides have a Frelon pad. The 4-sided bearing has all 4 sides with bearing plugs.
What is the dynamic load rating for a Frelon-lined bearing?
Plain bearings do not have a dynamic load rating, but are rated by their limiting PV, which is a combination of load over a given surface area and the velocity.

P – pressure or load in pounds per square inc (psi) or kilograms per square centimeter (kg/cm2).
V – velocity or surface speed in feet per minute (fpm or sfm) or meters per minute (m/min).
PV – pressure velocity value, P x V

NOTE: All three parameters must be met by an application for the bearing to perform properly. Max P times Max V does NOT equal Max PV: if one increases, the other must decrease in order to not exceed Max PV.
For a more in-depth look at PV, please see our blog: Calculating PV for a Plain Bearing
What is the max RPM (rotary application) for Simplicity?
Simplicity bearings are designed specifically for linear motion, and are not the ideal choice for high speed rotary applications.  However, when applied properly, Simplicity bearings will work very well in rotary applications. Stationary rotary applications do not allow the heat to be spread over an extended area – it is retained in the ID of the bearing, thus limiting speed and load.  - 40 sfm for precision ID - 140 sfm for compensated ID
What is the operating temperature for the Square bearings?
−400° F to 400° F (−240° C to 204° C)
What is the temperature range for Simplicity?
−400° F to 400° F (−240° C to 204° C)
What is the thread size for the lube fitting on bearings and housings that have the lube option?
¼-28 UNF thread
What lubrication is recommended for use with Frelon?
Recommended lubricants include:  way-lube oils, lightweight petroleum based oils and greases, or 3-in-1 type oils.  Lubrication can greatly increase the performance of a bearing when properly applied, but please refer to the catalog for detailed information.  
What seal materials are available?
Inch series seal materials include Polymod, urethane, and Viton.  Metric seals are available in urethane only.
What’s the difference between compensated and self-aligning?
Compensated refers to the ID of the bearing. Self-aligning refers to the capability of the bearing within a housing to “rock” in all directions to allow for some shaft deflection and misalignment.
What’s the difference between precision and compensated ID?
Simplicity bearings are available with two classes of running clearance.  Precision (FL) has the tightest running clearance of approximately .001” (.025mm).  This class is ideal for applications that require high precision.  Compensated (FLC) has additional clearance built into the ID of the bearing to .003” (.0381mm).  The FLC helps to accommodate or “compensate” for slight misalignments.
When I have both a standard and compensated fit Simplicity bearing how can I tell which is which when the bearings are not marked and no longer have the packaging?
A compensated fit bearing is looser fit to the shaft diameter, a simple method of checking would be to place both precision and compensated bearings on the shaft the compensated bearing should feel loose by comparison to the standard precision fit bearing.
Where can I find the housing bore tolerances which should be utilized for installation of Simplicity plain bearings?
Refer to Pages 138 - 141 (Installation Simplicity Linear Plain Bearings) in the appendix of the RST (Round Shaft Technology) Catalog
Why am I experiencing sticks, slips, and stutters using plain bearings?
As it relates to linear plain bearing technology stick-slip is often described as a temporary cycle of alternating rest and motion.  If this type of motion is repeatedly observed at the same location, then it is likely that an unknown force is acting upon the system at that location. The most common external forces are caused by misalignment or deflection of the linear shafts or an imperfection in the rail which can be caused by damage. Please see our blog Cantilevered Loads and the 2:1 Ratio for more detail.