Basic theory for ball bearing installation

In almost all instances the outer race is a slip fit in the housing, held staionary by use of spring or finger washers and/or threaded retaining rings. The inner race is often a press fit on a shaft, or in the case of a slip fit held fast with nuts, spacers or washers. In some special bearings set screws, notched inner races or other proprietary means are used.

Pushing the outer and inner races very slightly in opposite directions along the axis of the shaft is a techinque often used to provide pre-load. Pre-load is a method to remove some inherent play in the manufacture of standard duty ball bearings. Note that not all play can be removed, as the bearing would bind in operation.

How long do bearings last ?

Small bearings as found in many machine tools are considered consumable, to be replaced before becoming mechanically worn out. The determining measure of wear for bearings under normal usage is the lifespan of the grease. Bearing manufacturers put this as low as 2 years under continuous use operations. For intermittent shop use 7 years is a more realistic minimal lifespan. "Lubricated for life" bearings, as described, should not and cannot be relubricated. The impracticality of getting lubricant past bearing shields or seals as well as cleaning the old grease out makes replacement of the bearing the only viable solution.

Even sitting on a shelf, grease can calcify and degrade, rendering "NOS" (new old stock) bearings of questionable quality and value.

How do I know when it's time to change the bearings ?

It is best to change bearings on a schedule based on time in service, otherwise - when turned by hand, worn bearings may resist turning, feel erratic, and may seem "gritty". Under power they can be loud and high pitched. In extreme circumstances there may be excessive runout in the shaft/spindle, or sometimes a seized bearing can cause scoring of journals and/or shafts.

Note that the mass of the assembly that a suspect bearing is installed in, (e.g.; saw arbor or drill press spindle), will often mask the true condition of the bearing. Best to remove any old bearings before delivering a final verdict.

If a bearing race has spun on a shaft, can the shaft be repaired ?

Yes, sometimes by using silver brazing rod to build up the shaft and turning down to the proper diameter on a lathe. But it is a labor intensive operation.

What machines do you currently supply bearings for ?

Anything I should watch out for ?

Do I need any special tools ?

A 1 or 2 ton arbor press helps, as well as bearing pullers.  Snap ring pliers. If you're driving bearings off or on a shaft, a lead hammer or wood wallet should be used.  

Always keep in mind: bearings are a consumable commodity, just like brake pads or oil filters.