Queries on Drive Shaft

Forgot the attachment

if the drawing is near to scale i would suggest the angles are too steep.

universal joints do not transmit drive uniformly when operated at large deflections

http://en.wikipedia.org/wiki/Universal_joint

they are based on the hooke design so the output goes fast slow fast.

if you look at front wheel drive cars they have a different joint its called a constant velocity joint, its more complex but can deliver rotation at almost any angle of deflection

http://en.wikipedia.org/wiki/Constant-velocity_joint

http://www.bbc.co.uk/dna/h2g2/A693948

Peter,

Do you think thomson coupling will solve this issue?

Yes ive looked at their promo and looks ok.

http://www.thompsoncouplings.com/

In each case, shim the bearings so they split the difference in the angles coming and going. Make wedges or whatever you have to do. I would not put rubber mounts on the bearings, that would just allow the universal joints to impart vibration making stresses on the assembly.

Mike,

i didnt get your statement on " that would just allow the universal joints to impart vibration making stresses on the assembly". Could you please elaborate it further

After I posted that, I remembered my old truck having two driveshafts meeting at a center bearing, which was rubber mounted, so I guess it's ok to rubber mount such things. Some things you want to hold steady, so they don't start vibrating.

Once something starts vibrating, it can set up resonance and increase. You get weight in motion, and it acts against you.

I think a mould polisher or concrete vibrator can be good to see for your problem.

Sorry, Its a wrong post. should have posted at other place. (what you read is edited)

While your problem isn't uncommon the answers for it are. This is because there are many ways to solve it. The best is the use of double-cardan joints which aren't constant velocity but they are much closer to it than plain universals.

It seems to me that you have too sharp of an angle on at least one of the universal joints. You may need to add another universal joint or flange bearing near the one with the sharpest angle. I would also check the mounting hardware, brackets, and welds on the shaft and the metal wall to be sure everything is tight and sound and there are no broken welds or missing fasteners and the shaft is straight. If the shaft has been vibrating for very long there is a good chance you have some damage associated with the vibration.

I think you may need to install a new bearing and re-balance the vibrating shaft. Many times I have seen these sharp angles wear the bearings out and cause the shaft to become un-balanced from wear or bending. If the shaft is bent you can straighten it by by heating the bent area and cooling it with a wet rag to draw it back into alignment. BE CAREFUL NOT TO OVERHEAT THE SHAFT, IF IS MADE FROM CHROME MOLY OR OTHER HIGH STRENGTH ALLOY MATERIAL STAY BELOW 500 DEGREES F WHEN APPLYING HEAT..

I balance every drive shaft I build on my metal lathe unless they are to big and then I balance them on the piece of equipment they are from if possible. I do this by removing the end closest to the vibration being careful to just take out the weld and keep everything as square as possible. I mark the position of the end on the shaft so there will be an even gap around the shaft to prevent any one quarter of the weld from drawing more than the others.

After I am satisfied that the end is aligned correctly I tack it in one place and hand turn it a few revolutions so that it naturally finds the best alignment possible I weld a second tack 180 degrees out from the first tack. Once I get two good tacks on the shaft I will usually run the machinery for a short time to allow the joint to find its best balanced position . If the shaft runs at high RPMs it may be unsafe to run it with only two tacks because the rotating force on the shaft can shear or break the tacks. In this case I would hand turn it or try to run the equipment at a reduced speed if possible. Once I get it as close as possible I then tack it on two more positions (90 degrees out from the first two tacks)and the go back and cut the first two tacks and repeat the spin until it is balanced. After I get 4 evenly sized and spaced tacks on the shaft it is welded out in opposite quarters to minimize distortion.

When the shaft cools it is possible the stress from welding may draw the shaft a small amount out of balance, in this case I tack small pieces of metal to the "light side" and/or drill shallow holes to remove small amounts of weight on the "heavy side" of the shaft end to fine tune the balance. Do not drill on the the shaft tubing itself because the shafts are usually made from thin high strength tubing. Instead drill on the small balancing plates that you tack on the shaft or on the thicker end of the shaft. This will not help with your problem of having too sharp of an angle but even If you do reduce the angle I would still be sure to re-balance the shaft before running the unit.