Proper Shaft Coupling Installation

Proper installation can be critical in the function of rigid and flexible shaft couplings

Unless shaft couplings are carefully installed, problems can result affecting not only the function of the coupling but of the driving and driven components. Excessively large shaft misalignment can lead to premature coupling failure, and to larger-than-necessary reactive forces on support bearings, and to premature failure of these bearings. Improper hub mounting on the shaft can lead to the motor’s shaft getting torn up by the coupling, making removal very difficult, and degrading the performance of that coupling’s replacement.

While different types of couplings require different installation procedures, there are some general guidelines that can be applied to all. These can be separated into instructions for mounting flexible couplings and instructions for mounting rigid couplings; but many of the rules for mounting flexible also apply to rigid.

Installing Flexible Couplings:

We can break the process of installing a flexible coupling, typically consisting of two hubs with cylindrical clearance bores and one midsection, down into the following steps:

Hub installation: Both shafts should be clean, smooth, round, straight, and free of nicks. Driving component and driven component should be located near their final position, but at least one should still be capable of being moved. In most situations, a shaft-locking compound like Loctite© 603 retaining compound is recommended, as this increases engagement between shaft and bore and reduces the likelihood of destructive slippage during operation. Most of these compounds are non-permanent, and the hub will be removeable, with some effort; but the effort required to remove a hub that’s slipped, causing the set screw to chew up the shaft, or causing the hub to seize to the shaft, will be much greater.

Also recommended is the use of a non-permanent thread-locking compound on all set screws and clamping screws; Loctite© 222MS or Vibra-Tite© reuseable thread locker are both good choices.

With through-bores in the hubs, after application of a shaft-locking and thread-locking compounds, slide the two hubs over the two shafts and lock one hub into position, so that the end of the shaft is just short of coming through the other end of the bore. When tightening set screws, care should be taken not to strip the hexagonal socket. When tightening a hub with a clamping mechanism, care should be taken not to snap the head off of the screw.

With blind bores in the hubs, apply the locking compounds and push one hub all the way onto one shaft, and lock it down.

With keyed bores and shafts, apply the locking compounds, then slide the key into the shaft’s keyway, then slide the hub over both the shaft and key, and lock into position.

Midsection installation: Push the midsection onto the mounted hub. Push the unmounted hub into the midsection, and then lock it into position.

Align shafts: Even with flexible couplings, aligning the shafts as much as possible is critical to proper function. Methods for measuring and adjusting alignment will vary with the nature of the assembly, but in all cases, the installer must be aware of the different modes of misalignment possible, and must check and adjust for each.

The two shafts must be the same height above the mounting surface, and must both be parallel to this mounting surface; and the two shafts must have little radial misalignment as seen from an angle perpendicular to the mounting surface, and must be parallel to one another as seen from this angle. If adjustments are made to the two shafts to minimize each of these 4 modes of misalignment, the shafts will be well-aligned.

Lock down the second component: Be sure to check height above the mounting surface after tightening the bolts that hold this second component down, to be sure that the shafts are still the same height. Use shim if necessary to bring them up to the same height and angle.

Installing Rigid Couplings:

Many of the steps for installing flexible couplings apply equally well to rigid couplings. Of course, in the case of rigid couplings, good shaft alignment becomes much more important. The couplings themselves can be used as fixtures to “force” the two shafts into alignment before locking one of the components in place.

One-piece rigid couplings: Check shaft heights before installation; then loosen one component, install coupling, tighten coupling, and tighten component.

Three-piece clamping rigid couplings: These can be installed in the same way as one-piece couplings, or the installer can first fully align the shafts and lock the two components down and then install the coupling without moving either component (the same option as is available with flexible couplings with through-bore hubs).

written by:
Steven Elliott
OEP Couplings,
a division of Oren Elliott Products, Inc.