Shaft alignement

If you are using universal joints , what is the tolerance or allowed maximum offset? What are you driving ? What is the Speed of the primary Mover?

If your using an universal joint, there is no advantage to have them in perfect alignment.

Hello Guest

Be very careful in the installation of a shaft with a universal joint at each end. Universal joint I refer to has four small bearings on the ends of a four legged cross piece, which I will call "the spider". The spider then connects to two outer "fingers". The following are my tips:

1. The spiders must be in perfect angular alignment with each other. By looking along the drive shaft, all four ends of the two spiders must be in perfect alignment. If not vibration will appear on light structures, or bending stress will be there ( but not all that apparent) and cause premature bearing failure.

2. The driver and the driven shafts/couplings must be parallel with each other if none of the symptoms from 1 above are to be induced.

3. Both the drive and the driven halves of the fingers (the ones NOT on the coupling shaft) must be set correctly. This is that the bearings in one must be at 90 degrees to the opposite one. This enables the two spiders to work (they oscillate to and fro on each revolution). Without this the spiders actually "click" or "flick" as they pass each half rotation setting up the problems in 1.

4. If the shaft has a slip joint (as in motor car rear wheel drives) then the manufacturer normally adds alignment marks to each side to ensure that they are assembled in the correct radial angular position.

I have had plenty of experiences. Two that spring to mind are the flywheel of a diesel engine was connected to a drive but the connecting shaft had a universal joint on one end only. This broke the engine crankshaft a few times until the cause was found. Another case saw the engines driving a jet drive on a boat. There were three universal joints in the drive, one being in the near centre of the shaft to enable a wider angle. They were never going to work and so I re aligned the shaft by adjusting the height of the centre joint. Problem solved!

By the way, if not a universal joint, it might be a CV joint. CV joints can do the same job, but are quite different in their mechanics

To answer the question...the alignment is not critical, its the application and understanding of how they work that needs to be understood. The universal joint is known in more technical circles as "Hookes Coupling" If you Google this you can get plenty of info.

Sorry to be so long winded !!