Spindle bearing replacement for CNC mill.

[Spindel]

I'm rebuilding a CNC milling machine, and the bearings for the spindle are worn out(coolant corrosion)
And i want to replace the main roller bearing and the ball bearings.
Roller bearing : NN3007K
Ball bearing: 7008AC/TBTB x 3
These bearings are not that common and they need to be at least P4 rated, but the problem is that the price from SKF is a bit on the high side,( they wanted 1500$) As this machine is used for hobby use, i don't intend on using that kind of money just for bearings.

I've talked to some chineese bearing suppliers. They can supply the same bearings for 350$. But i'm a bit worried about the quality of these bearings. Does anybody have any tips to give regarding affordable bearing suppliers?
Having a bad spindle can make a lot of other problems, so i'm seeking help here

Quote from Chinese bearing supplier.

Picture of spindle assembly and forum thread of spindle repair if you are interested

Regards

 

[tbuelna]

Does anybody have any tips to give regarding affordable bearing suppliers?

Unfortunately, milling machine spindle replacement bearing sets are a case of you-get-what-you-pay-for. Precision class, matched sets, material quality, manufacturing process control and QA, etc. are all factors that affect cost. The premium you pay for bearings from an established manufacturer like SKF, NTN, NSK, FAG, etc. is so you can be confident the quality/performance will be what the manufacturer claims. You have no practical way to verify the bearings you purchase were manufactured correctly and comply with ISO/ABEC requirements. You basically have to take the manufacturers word for it, so reputation is everything.

The 7008AC/TBTB part number describes a matched set of three 25deg angular contact bearings 40x68x15, arranged back-to-back and tandem, with light axial preload. The photo above appears to show a four bearing set. Which is correct?

 

[Spindel]

Hello, thanks for the reply, the photo appears to have 4 bearings sets, but one of the rings are just a spacer ring.

 

[SwinnyGG]

According to your post in your forum thread you've already ordered bearings... so did you buy the Chinese sourced set?

The supplier listed by another poster in that thread apparently has the correct bearings in stock for a small premium over your Chinese source...

 

[Spindel]

Hello, we ordered new SKF bearings. Thanks for the reply, maybe i will try Chinese bearings in the feature for a less critical job.

 

[Tmoose]

Ever assemble a precision spindle before ?

Installing the new taper bore (K suffix) roller bearing is T-R-I-C-K-Y .
If grease lubricated, For all but the lowest speed applications, the choice of grease is critical.
Don't experiment with anything but Kluber, SKF, or FAG recommended products. Especially don't try any of the specialty hi temperature etc grease suppliers. They almost certainly will be experimenting with you, and and your $1500.
There are marks on the bearings' inner races that can (must) be used along with bare spindle measurements, to assemble and minimize the spindle taper runout.
If the first bearings failed by coolant ingress, the sealing arrangement might need an upgrade.
If grease lubed, a careful break-in procedure monitoring spindle temperature real time may be necessary to avoid infant mortality from over heating.