Robert Giesen 
B & B Electric Motor Co. 
Wichita, Kansas 
Technical Education Committee Member 

Editor's Note: The procedures outlined in this article exclude explosion proof motor end bracket rebuilding.  

Many motor service centers bore and sleeve end brackets (end bells) in machine lathes. When using a lathe you need one large enough to swing the outside diameter of the end bracket and the large mass is hard to indicate true. Many times it is difficult to clamp onto the lathe chuck or faceplate. 

When rotating a large mass there is always a chance of the part coming loose and causing damage to the end bracket or injury to the machine opera­tor. We have bored and sleeved end brackets for more than 25 years in a vertical milling machine. We find the mill is a more useful machine; it is faster and more accurate to indicate in and set up. 

The boring of the diameters are true and concentric and it is much safer to rotate a cutting tool and not the part. Following is a step-by-step procedure to bore and sleeve end brackets in a verti­cal milling machine. 

Secure to mill table 
First, clean the end bracket and check for a flat surface to secure it to the mill table. If you do not have a flat surface you can turn the end bracket over, supporting it on the machined areas, and make a light fly cut across the outside end of the end bracket to obtain a flat area. 

The end bracket can be clamped to the mill table by using a bolt and washer large enough to fill the exit hole and se­curing it to a T nut in the mill table. 
In some cases it may be necessary to support the end bracket with blocks and clamp it at the block supports. Caution needs to be taken not to distort the end bracket when clamping.

Sometimes it may be necessary to drill a hole in the end bracket center to clamp it to the mill table. The hole can be tapped and plugged with a setscrew when the machine work is finished. 

End Bbracket boring 
Use an adjustable tool holder in the milling ma­chine spindle to hold the cutting tool for boring of the end bracket. Select the proper cutting tool to bore the housing and set the depth gauge to stop the cutter from going too deep into the housing. 

Attach a dial indicator to your adjustable tool holder and indicate the outer flange for flatness by rotating the indicator around the housing (Figure 1). By tilting the milling machine head you can obtain the correct plane for true indication (or use leveling blocks under the end bracket bolt hole). 

Next indicate the inside flange by moving the indicator around the flange. Adjust the mill table right and left / in and out to ob­tain true indication. Lock all of your adjustments and proceed to remove material from the bearing bore. 

Check outside diameter 
Select the sleeve material to be used and mic the outside diameter. Check the outside diameter at different points for roundness of material and select a dimen­sion that will give you a .003” to .004” press (.08-0.1 mm) fit. 

Bore the housing to give the proper fit for the new sleeve material (Figure 2). When finished boring be sure to vacuum all cuttings for the hous­ing before inserting the sleeve. 

Use cast iron sleeves when possible since you’re using like material; the expansion and con­traction will be the same to eliminate the possibility of the sleeve coming loose in the hous­ing. In some cases it may be necessary to machine a sleeve from steel tubing or stock. 

Select the proper sleeve and cut the sleeve to a length slightly longer than the depth of the housing. For many years, we have used cast iron engine cylinder sleeves. The cost of the sleeves are less than purchasing sleeves from suppliers. Some sleeves can’t be bought in the correct dimensions for ball bearing sizes; in this case you will need to purchase a precut sleeve.

Use bearing mount adhesive 
Prior to installing the over the end of the sleeve and driving the sleeve into the housing using a soft face mal­let. An alternative is to freeze the sleeve to shrink it and just drop it into place. Then use the mill head to press in the sleeve. It is not neces­sary to remove the end bracket from the mill table (Figure 3). 

Re-indicate the end bracket after inserting the sleeve. Follow the above procedure for indication. 

Machine the inserted sleeve to the proper fit for the bearing outside diameter. (See “EASA Cylindrical Roller Bearing Fit Tolerances” and “Radial Ball Bearing Fit Tolerances” charts in the EASA Technical Manual, Mechanical Refer­ence Handbook or laminated versions.) 

Chamfer inside edge 
After machining to the proper bearing size, face the end of the sleeve flush with the original housing. Insert a chamfering tool and chamfer the inside edge to make it easier to install the bearing into the housing (Figure 4). Vacuum the cuttings from the housing. 

Before removing the end bell from the mill table verify that the shaft opening is concentric with the bearing diameter. If the hole is not concentric it will be necessary to bore and sleeve the exit hole. 

I recommend using brass or aluminum for sleeve material to prevent shaft damage in future failures. Follow the same boring procedures and give the proper clearance for the shaft. It may be necessary to re-clamp to bore the exit hole. 

Thoroughly clean the end bracket housing prior to installing onto the rotor and stator. 

We have also had great success boring large sleeve bearings in the mill, and having very little, if any, binding or heating of the finished bearing. If you have a milling machine try this process; 

I believe you will find it will take less time, keep the repair cost down for your customer and give a better housing repair.

Categories: Bearings, Repair procedures & tips, Service center equipment

Tags: Bearing housings End brackets/end bells

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