Universal Shaft Joint

You give too little detail of the actual equipment for a definitive answer, but be aware that you not only have a maximum misalignment angle, but equally important a minimum. Somewhere round about 0.5 deg minimum to around 1.5 to 2 degrees maximum would not be uncommon. (Best way is to contact the manufacturer and get his recommendations)

The professor is always right

What is the power transmitted, the RPM (at the copling stage) etc are all required parameters. Also what are the problems you are facing with the coupling will give us some idea about the cause of the problem.

The question is not what is the maximum allowed. Try to keep always the alignment within minimum achievable/measurable to give best life not only to your coplings but also the shaft bearings - roll side and gear box side. Improve the system efficiency and in extreme cases (we have seen in very heavy duty equipments) save the gearboxes, shafts etc.

"but equally important a minimum."

Are you saying that it would be bad to have zero misalignment angle? I find that hard to believe. Some kinds of flexible joints would have more play when aligned than misaligned, but if that's a problem then a different kind of joint should be chosen. There are many kinds and brands, each with strengths and weaknesses.

dkwarner,

Yes sir, that is exactly what I am saying, but maybe not clearly enough.

This angular misalignment (offset) is required on Cardan shafts to ensure lubrication of the joints.

The driver and driven however, need to be parallel relative to each other. Maybe the attached document will explain it better than I am doing.

http://www.ludeca.com/casestudy/telediag0606-1.pdf

I had never heard the term 'Cardan Shaft' before. I gather (from Wikipedia) that it is a mostly European term. It still is not entirely clear whether the term would be used when a single flexible joint is employed to join two shafts, or only when an intermediate shaft with two flexible joints is used.

I do understand how a small movement in the joint would continuously move lubricant around within the joint, but if the two shafts were so perfectly aligned that no movement exists, then no lubrication should be required!

As I believe I stated in another post, my experience with flexible couplings is with low power levels, and most of the dozen or so different couplings I have tried use no lubricant at all. We commonly use the helical joints illustrated by gsuhas, and to join gearboxes to rolls, as in the OP's original question, we use Lovejoys.

Sorry about the Cardan word - European upbringing coming through.

I would (rightly or wrongly) use the term Cardan joint completely interchangeably with Universal joint. Though I have never really thought about it, when I refer to a cardan "shaft" I do tend to mean two joints and an intermediate shaft.

I have never used a single universal joint to couple two machines as the velocity variations are too great and can cause problems not encountered with other types of flexible couplings. The two joints with an intermediate shaft like a motor car prop shaft tend to cancel out this problem and give an almost constant velocity if the angles are not too great.

"if the two shafts were so perfectly aligned that no movement exists, then no lubrication should be required!" True, but then a rigid coupling would be the first choice.

I just assumed that the OP referred to a double joint.

Thanks.

I've gone back to read the original post several times, and I'm still not absolutely sure how to interpret it. When I read 'universal shaft joint', I thought of 'flexible coupling', not 'universal joint', because that is what we use. In most of the places where I have used flexible couplings, their principal purpose is to allow less-than-perfect shaft axial alignment, and a single U-joint, of the kind used in automotive drive shafts, does not serve that purpose.

Hi Zmun

I have some pointers for you, notwithstanding the previous comments:-

a) Yes, there is a minimum angle that a UJ should be driven at, the reason is to provide enough movement in the joint for the needle rollers to lubricate.

b) Yes, there is a maximum permissible angle to drive the UJ at. This is a manufacturer's specification but would normally be around 45° (perhaps optomistic)!

c) If you need constant velocity on the output shaft and you have an axial miss-alignment, you must provide TWO UJ's with equal but opposite angles. This is critically important otherwise, as the output shaft turns, there will be an increasing and decreasing velocity each revolution.

d) Unless the input shaft and the output shaft are supported from the same RIDGED structure, you will also need a section of the PTO/shaft that can telescope. This needs providing for in the build.

I'm sure that there is more that we could all say on this subject but without specific info......!

Good luck with it!

Also please remember that the Universal coupling output speed is not directly same as input. Though rpm of input and output are same, angular velocities are different angle to angle.

There are better types of couplings like, helical flexible couplings.

http://www.rw-america.com/shaft-couplings-line-shafts/index.php is just an example. You may find many more suppliers.

Or you may contact me, I can suggest supplier from India, who can supply these at very low rates as compared to others from USA/ Europe.

Try this website

http://www.johnsonpower.com/paper.html

Look under Installation & Maintenance

Jim C

after reading the other posts i did not see much about lubrication. that is the biggest problem i see in the real world. we change many u-joints here and thats the biggest reason that i see for replacement. sounds like the other posts are accurate too. remember, "if you love it lube it".

Please note Flexible shaft coupling (Helical) doesn't need lubrication.

Your post indicates concern about angular misalignment, and that is clearly a concern, but so far no one has mentioned shaft offset or axial misalignment. It is quite possible (in fact probable in many cases) for shafts to be accurately parallel, but not accurately in line. Some types of universal joints are more forgiving than others for any specific kind of misalignment.

You would probably get more useful information if you supply Brand/part numbers and/or photos of the kind(s) of joints you are dealing with, in addition to torque and speed requirements.

"but so far no one has mentioned shaft offset or axial misalignment."

Yes, we did! In #4!

Oops - Sorry, I missed that! I stand corrected!

I had also missed your reason for a minimum alignment... Very few of the many kinds of flexible couplings I have used recently (all low power) require lubrication, so that would not apply. I also stand a bit more educated. Thanks!

Is it possible to reposition the gearbox and use double-row roller chain? Very durable if properly sized.