Quote:
Originally Posted by Cothron Theiss
This is a pretty significant tangent, but it's not worth making a new thread over. What actually happens when you overconstrain a shaft? Does it automatically bind? Is it somewhat more prone to binding? Is the resistance (load) substantially increased? I know not to do it, but I don't know that actual effects of doing it.
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If you have a significant gap between bearings and good manufacturing/assembly tolerances (as in James' example above), you won't see much negative impact to performance.
Some potential effects:
1) You won't be able to install the shaft. This is an easy problem to spot. You have three bearings, try to slide the shaft in, and no dice.
2) You figure out a way to install the shaft, with a axially mis-aligned set of three bearings (maybe you constrained the bearings to a rigid member AFTER installing the shaft). In this scenario:
2a) The shaft rotates, but with additional load due to the shaft constantly bending/additional radial load on bearing. This inefficiency can sometimes be hard to spot right away, but can suck power from your system
2b) The whole thing seizes up and won't move. I've seen this happen, especially when the torque applied to the shaft is fairly weak (obviously, since the system is more susceptible to inefficiencies).
Like Chris said, do it right, and you won't have issues. But people don't always do it right, so it is important to understand where things can go wrong.
Best,
-Mike