Alignment Problem In Universal Coupling

I have never heard about a coupling that needs the input and output shafts to have a misalignment to work well. Everybody uses laser alignment devices to align motors and driven devices as much as possible to avoid unwanted loads in the joint and the bearings and maximize equipment life...

Aren't you talking about the phase angle between two cross type joints in a shaft?

Yes good point i was thinking of that too! with only one joint and the high speed of most pump types any misalignment would cause vibration. However, this only applies to U joints with bearings solid U joints of Rubber or cloth tend to damp the vibration to zero by the twisting action in the joint material and the necessity of the whole shaft to turn together. personally if it is a centrifugal pump or the pump shaft is self supporting i'd hard couple it to the motor and fix the motor in position to the pump case

You´d be well advised to disregard that advice. Any misalignament is bound to induce vibration and lead to coupling wear and early failure. Shaft to shaft misalignment costs billions in down time and maintenance worldwide.

The suggestion for purposefully misaligning the universal joint is to create some movement in the u-joint bearings so they don't sieze up. However, in your application I would also suggest a hard couple as a single U-Joint at an angle will cause vibration.

Tis my comsidered opnion that who ever told you that you need a missalignment is right and wrong. IF you are using a COUPLING then , no you do not want any missalignment. IF you are using a driveshaft with universal joints, then yes you do want about 3 deg. missalignment. The reason for the 3 deg. missalignment is so the needle bearings in the u-joint move. That helps keeping the lubricant in there moveing and the needles won't wear grooves in the caps and cross shaft. Check with the vender that you got,or would get a similar coupler from and see what they say.

By the way don't take the words all in caps as yelling I only did that to accent the item I was refering to.

If it is a gear or disk coupling, line it up dead on.

If it is universal (U) joints then if it is dead straight the needles hammer into the race and it is destroyed, so the input and out put shaft need to be offset but parallel. The knuckles must be dead in phase. About 3 deg of angle at each joint is good.

If the knuckles are not aligned or the input and output shafts are not parallel then an angular acceleration occurs and you get vibration.

If you can line up dead on you may want to consider zero backlash couplings (disk couplings or shim pack) that will absorb the very slight misalignments but be grease-less and maintenance free.

There are also a number of synthetic couplings that will absorb torque vibrations, but are not rotationally stiff. Selection depends on what you are trying to achieve.

hilltopper is correct. If thermal growth is a consideration you want to make sure that your cold alignment accounts for the minimum missalignment during operating conditions. visit www.ameridrives.com ; I have found them to be a very reliable technical resource on this very topic.

I can't stand it! I must comment. Our dear guest is connecting, likely, an engine to an irrigation right angle gear drive and vertical pump or straight to a pump. This is a "Cardan shaft" or a "drive shaft" as we say over in here USA. YES, you misalign it off the horizontal / vertical plane (I don't care which) 3 - 15 degrees, but check with the shaft manufacturer as some allow more. This rolls the needle bearings in the grease in the U-Joint caps and distributes the hammering load (torsional vibration) common in engines. If you line it up straight, they won't roll and will brinell (flatten) on one side in a few weeks / months and lock up and come apart. I assume you have a shaft length of a half meter or more. Now the other misalignment is to be avoided and that is angular misalignment, where the faces of the U-Joints are not PERFECTLY parallel. Most U-Joint suppliers allow only up to 2 degrees angular misalignment. This angular misalignment stresses the yokes and they will fatigue crack.

George (the engine dude)

PetroPower, thank you for an excellent technical summary.