Part 2 of How to replace damaged bearings on a precision CNC spindle
There are a lot of questions about replacing bearings on CNC spindles. As a result, we’ve decided to write a 5-part series of articles to help shops replace damaged bearings themselves. Should you run into trouble replacing the bearings yourself or have a question, email or call us. We’ll do our best to help. Email us at [email protected] or call 1-603-483-0333
- Introduction
- Part 1: Disassembling Your Spindle
- Part 2: About Angular Contact Bearings and Lubrication
- Part 3: Angular Contact Bearing Installation Arrangement and Preload
- Part 4: About Cylindrical Roller Bearings Installation and Preload
- Part 5: About Capture, Specialty Bearings and Hydraulic Nuts
Angular Contact Bearings, lubrication and how to preload them
In Part 1 we considered some tips on getting your spindle apart. Now we will need to get and install the correct bearings. Part 2 focuses on Angular Contact Bearings, lubrication and how to preload them.
Super Precision Spindle Bearings
When we’re speaking about bearings on a CNC spindle we’re speaking about two different types, Angular Contact and Cylindrical Roller Bearings (CRB). In a few instances, there may be deep groove type bearing and an occasional cup and cone. Their installation is usually straight forward and they are not going to be discussed in this article.
Angular Contact Bearings (ACB) can handle axial and radial loads and are considered thrust bearings. However, they can only handle axial loading in one direction; so they are always used in pairs. Roller bearings have tremendous radial capacity; but zero axial capacity. So if your spindle uses a CRB it will also have at least one pair of ACBs.
Because we warranty all of our work HST only uses top name brand bearings purchased from authorized distributors. We simply can’t take the chance that an inferior bearing will fail prematurely. These bearings have one thing in common; they are expensive. However, the DIY guy may want to take a chance and use some “off brand” bearings. Depending on the spindle, the price difference could be over a thousand dollars.
If you have a problem locating a bearing give us a call. We may be able to help you find a source and assist with the installation of spindle bearings.
About Angular Contact Bearings
High performance CNC spindles use Super Precision ABEC 7, ABEC 9 or P4 spindle bearings. For a long time these were purchased as a matched set. We always prefer matched sets. However, today matched sets are becoming more difficult to find and there is an industry movement toward P4 singles. The theory is that any P4 bearing will be within the tolerance specification for matched set.
As noted these Angular Contact Bearings (ACBs) can only resist axial loads in one direction. For this reason they must be used in multiple bearing arrangements to handle thrust loads in both directions. These bearings come configured in a number of different arrangements. To get started let’s take a look at an angular contact bearing.
The first thing to know is that ACBs have a front and a back. It is import to be able to identify which side is which. Most often bearing nomenclature is printed on the back of the bearing. But that is not always the case so it is good to be able to identify which side is which by looking at the bearing. If a bearing is installed backwards the spindle will not perform satisfactorily and the bearing is likely to be ruined.
Note in the diagram that the bearing can resist thrust on the shaft pushing from front to back. If any significant thrust is applied back to front the bearing can separate and be ruined. It is easy to see why when you look at the cross section.
Getting the Right Bearing
Bearing Installation Notes
Preparing Bearings for Installation
Lubrication
