May 12, 2012
From the Mailbag: Mounting to Coupling Hubs
By Stan Riddle
QUESTION: When mounting the lasers, if it isn’t possible to mount to the shafts, can they be mounted to a flanged sleeve gear type coupling? (The outer “floating hub”, not the inner one pressed on the shaft.) I have seen this done and do not think it is accurate due to the radial clearance between the inner and outer hubs, but others disagree. Thanks!
ANSWER: You are correct. Laser shaft alignment tools work great when mounted to a solid surface, whether it is the shaft or the coupling hubs. But if you mount on the coupling insert, sleeve, or anything else that can flex during the shaft alignment process, it will give you inaccurate results. This is true for laser alignment systems or dial indicators. The reason is the insert, by definition, “floats” or moves during rotation.
If by “floating hub”, you mean something like a Falk Steelflex, with a grid-type connecting “spring”, the hub moves on O-rings, which are mounted to the couplings hubs. It is simply a “cover” to hold grease in and dirt out, and should not be used as a precision surface for shaft alignment either.