Lufa Bearings

Lufa Bearings

WHAT’S THE LUFA ROD END ?

Basically, the Lufa Rod End is a two-piece non-swaged spherical bearing. Undeniably, a two-piece rod end has greater radial static load carrying capability then that of a three piece design. A three piece rod end has a ball, a race swaged around the ball, and then the ball and race assembly staked into a rod end body (banjo).

A Lufa rod end has only two components…a ball and a banjo. Both components are tolerance machined to predetermined dimensions offering zero breakaway torque ensuring absolute surface contact area interface. The banjo head’s wall thickness is the same as the combined thickness of a three piece. Having two rod ends produced from identical materials, the Lufa will be stronger simply by design characteristics.

The Lufa design accommodates any machine capable material in any design configuration or any size desired by the end users. Cradin produces solid aluminum rod ends having a fluoropolymer coating applied to the ball surface to gain lubrication. Want a solid composite ball instead, not a problem. The advantage of a Lufa rod end is the ball element is easily replaceable. Meaning, you really don’t have to replace the entire rod end just the ball.
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More About the Lufa Bearing

Self-lubrication, now here’s a touchy subject. You have the homogeneous (black stuff) injected inside the race that supposedly encapsulates the ball without creating air pockets. Once cured, the black stuff bonds to the race but not to the ball. How do they do that? The black stuff sticks (bonds) to one part but not the other. Must be something magical applied to the ball’s surface to discourages surface bonding; which, I would think, introduces surface degradation leading to premature bearing failure…Or, simply the black stuff de-bonds and falls out. Which introduces the question of having a race to ball clearance significant enough (probably .015” to .030” per side) to allow the black stuff to readily flow inside between the ball and race. How do they keep the ball centered or from floating around during the cure cycle? Must involve some complicated fixtures.

PTFE (polytetrafluoroethylene) fabric impregnated self-lubricating liner systems, the time proven “dry wing” application solution. With all the advancement in composite materials one might consider them a bit archaic…but, hey, it’s worked for years. However, you have exactly the same problems associated with the black stuff. Everyone involved with self-lubricated spherical bearings has experienced liner de-lamination and/or liner de-bonding from the race…sometimes before the bearing was placed in operation. How about moisture absorption? Ever had a bearing get tight during a humid day while it was just sitting on your desk? This phenomena is often referenced as wicking (as in a candle wick) the problem is, once the fabric wicks or absorbs liquid (be it de-icing fluid, water, oil, etc.) the fabric strand literally release from the surrounding bonding resin system. Once this occurs, the bearing is doomed for failure.

Wouldn’t it be advantageous to have the ball element produced from an advanced composite material? You wouldn’t have liner de-lamination problems, because the liner system is the actual ball material. You wouldn’t have any wicking concerns or liner de-bonding issues, because you not dealing with a .012” to .014” thick resin impregnated woven fabric.

The Lufa bearing offers all of the above stated advantages…Plus more! There are no size restrictions associated swaged spherical bearings. The Lufa is completely machined. Material combinations are unlimited.

The Lufa design concept, a two-piece non-swaged spherical bearing, allows the use of detail components produced from exotic materials previously considered non-economical to produce. As an example, take a rod end having a titanium body and a carbon-graphite ball. This particular material combination has definite advantages when used in specific applications…the strength of titanium and the self-lubrication and low coefficient of friction properties of carbon-graphite. However, this material combination was once considered unthinkable because titanium doesn’t lend itself to cold forming (swaging) and a carbon-graphite ball could never be used as a bearing race forming member (it would crush). Cradin successfully produces this material combination rod end for use in throttle linkage.

The ultimate in strength, durability, weight savings and non-corrosiveness would be a 100% titanium rod end, but rubbing titanium parts, especially under load, results in severe galling. Cradin Aerospace has successfully produced this particular bearing assembly by having the interfacing titanium component contact surfaces separated by a thin (.0005”) surface deposition process which also offer self-lubrication.

The Lufa design accommodates any machine capable material in any design configuration or any size desired by the end users. Cradin produces solid aluminum rod ends having a fluoropolymer coating applied to the ball surface to gain lubrication. Want a solid composite ball instead, not a problem. The advantage of a Lufa rod end is the ball element is easily replaceable. Meaning, you really don’t have to replace the entire rod end just the ball.

Because the Lufa is a non-swaged bearing, all established required dimensions are controlled during the manufacturing processes. Lufa rod ends have zero breakaway torque and require no break-in to loosen them up. The established internal tolerances held during manufacture are maintained throughout the operational life of the rod end. Cradin’s high mis-alignment Lufa bearings and rod ends do not have the traditional stepped balls. They have a complete ball sphere which allows for greater mis-alignment deflection during cyclic actuation movement.

Cradin Aerospace does not employ traditional bearing self-lubrication by incorporating polytetrafluoroethylene (PTFE) impregnated in a fabric material bonded to the inside diameter of the bearing race. Our in-house testing continually demonstrates liner delamination and failure . The PTFE liner systems are considered, by Cradin Aerospace, to be old technology. With the rapid and continual advancement of composite materials and surface treatments, Cradin has elected to offer rod ends having ball elements produced from solid composite materials demonstrating low coefficient of friction and elevated temperature operational capabilities. For metal-to-metal rod end configurations, we apply fluoropolymer coatings to the ball. It should be note that the Lufa is not and should not be confused with a Messerschmidt (loader slot) bearing. By design, a loader slot bearing sacrifices a significant amount of the race material to gain ball entry, which normally requires the addition of material mass (weight) added towards compensating for the loss in radial static load carrying capability. The Lufa is dimensionally the same as “standard” specified rod ends.