Installing new spindle bearings

[bilinghm]

Hello,

I am planning to install new spindle bearings in an X2 mini mill and need expert advice getting the new bearings into place without damage. The old ones were very tightly press fitted and I successfully removed them with a puller. The new upper and lower bearings must press fit into the head/housing, and the spindle shaft must then press into the bearings.

I am thinking heating/freezing, but I sure would appreciate any good advice from anyone that has done this before.

Thanks,

Bill

[cam1]

I'd recommend measuring the boreand shaft that the bearings are going to be pressed into first. Then, select your bearings, and verify that the housing to bearing OD fit is appropriate. Heat/shrink fits are fine, but the amount of interferance has to be correct with respect to the bearing and it's intended application.Too tight, and the bearing will fail (reduced ball to outer race clearance). Spindle /precision bearings rely on very minimal radial clearance to acheive accurate runouts. On housing to OD fits, only the outer race can be pushed on. If you install the bearings by forcing/hammering on the inner race, you will ruin the bearing.On shaft fits, you can only apply force on this inner race. The reason for this is that you do not want to tranmit force/shock loads through the balls.

regards

[bilinghm]

Do I understand you that the outside bearing race should be a press/shrink fit and that the inside/spindle side should be a looser fit?

Originally Posted by cam1 I'd recommend measuring the boreand shaft that the bearings are going to be pressed into first. Then, select your bearings, and verify that the housing to bearing OD fit is appropriate. Heat/shrink fits are fine, but the amount of interferance has to be correct with respect to the bearing and it's intended application.Too tight, and the bearing will fail (reduced ball to outer race clearance). Spindle /precision bearings rely on very minimal radial clearance to acheive accurate runouts. On housing to OD fits, only the outer race can be pushed on. If you install the bearings by forcing/hammering on the inner race, you will ruin the bearing.On shaft fits, you can only apply force on this inner race. The reason for this is that you do not want to tranmit force/shock loads through the balls. regards

[cam1]

Hi: Typically you would use angular contact bearings, with the outer race fixed at the lower end, and the opposite bearing outer race end free(sliding fit), with a preload washer. This preloads the bearing The inner races would be a light press fit onto the shaft. This arrangement allows the shaft to expand (grow) away from the cutter.

Please refer to attached document

regards

[cam1]

Here is the attachement....

[bilinghm]

cam1,

I see your point. Angular contact would be ideal. The standard set up is deep groove radial bearings. I will have to do some major rethinking to go angular contact.

Thanks!

[cam1]

Bill: Angular contact is a way to go, and provided that you have the room to install them, it would be an improvement over palin deep groove bearings.
Just 1 question: what is the reason for changing the old bearings?

regards

[bilinghm]

I have the machine completely apart, and I decided to investigate the beatings prior to increasing the spindle speed (from 2,500 to 5,000). The bearings are "no name" units that look pretty modest in terms of quality.

Originally Posted by cam1 Bill: Angular contact is a way to go, and provided that you have the room to install them, it would be an improvement over palin deep groove bearings. Just 1 question: what is the reason for changing the old bearings? regards

[cam1]

Hi: Another way to go is to use a higher quality deep groove bearing. (Spindle Bearing)
Try this link for some more info:
http://www.pacamor.com/technical/abe...ances.ssi1.php
This may be a more "linear way" of solving the problem, and the 5000 RPM will not be that difficult to acheive, even with grease lubrication. I still recommend getting the Engineering info from the bearing manufacturer that you select (just ask for some photocopies from the bearing shop).
You will want to verify the shaft to inner race fits and the outer race to housing fit.
The bearings should slide into the housing without having to be beaten on. At the most I'd anticipate a light press fit. (housing ID = bearing OD-.0001).The bearings are typically encapsulated, and held in place with a Cap. The loads are relatively light, and what is important is bearing stiffness, and circularity.

regards

[mc-motorsports]

I rebuilt high end spindles for 9 years. Looking at that blueprint you posted, the two bearings at the top and the two at the bottom are angular contact, the one in the middle is a radial. As far as mounting the new bearings, polish the shaft so it is free of any defects, scrathes, gouges, anything that would stick up and I don't nessessaritly mean make it look like chrome or use sandpaper, maybe just rub it with a stone, ect. Use a heat gun to heat the ID of the bearings SLOWLY, I really can't tell you a temp, probably 180*F, I go by feel, if you do it right, the bearing will slip right over the shaft, but you will only have about 1 second literaly once the ID of that bearing touches that shaft before it shrinks and grabs.

Bearing ID's are generally made to be press fit on shafts and accept a certian amount of distortion accordingly. OD' generally do not like any kind of press-fit. The OD of the bearing should be a gentle slip fit into thier bore and are either held in place by the bearing pre-load or a cover which is bolted down and you wouldn't want more than .0015" inteference. Any spacers between two angular contact bearings should be parralel and flat within .0002", little overkill for a low RPM spindle, but good practice.

And new bearings should be fallowed up by proper balancing. It will help the spindle performance as well as extend the bearing life, it's a win win situation.
Good luck!

[bilinghm]

The mini mill spindle is supported by two radial bearings, a 6206 and a 6007. The measurements are:

OD Bore: 61.90 mm (Both 6206 and 6007)
OD Bearing 61.99 mm " " " "

ID Bore 34.97 mm (6007 bearing 29.96 mm)
ID Shaft 35.01 mm (6007 bearing 30.00 mm)

Are these bore/bearing/shaft fits appropriate for a spindle? They are all pretty tight.

[cam1]

Hi: Looks a bit tight : Bore ID 61.90 - Bearing OD 61.90 = -.09mm or .0035 inch. Thats really too tight for the OD.

regards