Bridgeport Spindle Bearings

[fredhh47]

OK, I was going to add this to my other question, but thought better of it. My 3 Bridgeport CNCs, Boss 5 and Boss 9 (Ser I), and Boss 6 (Ser II), could all benefit from new spindle bearings. The last time I replaced a set of them, B'port was still in business and it cost a small fortune for a "matched" set of bearings. What are the chances of using standard replacements and getting good results, or do I have to find a source for "matched" sets? If the latter is true, where can I find "matched" sets and at what cost? Thanks. Fred Howe

[machintek]

Yes, they are not cheap, but a google search may get you good results.
Personally, I do not rebuild the spindles unless a customer is not concerned about holding very tight tolerance. I send mine to C & M precision spindles in Tualatin, Oregon. I have been doing this for about 12 years. For about the cost of the bearings from Hardinge, they will rebuild the spindle, pre-loading it correctly and regrinding the spindle tool holder surface while running in the new bearings to get the runout at close to zero as possible. I cannot do that in the field.
1-503-691-0955.

George

[fredhh47]

Thanks for the suggestion, George. I may give them a try. Fred

[NC Cams]

I concur with George and add the following:

The OEM bearings were precision matched for tolerance, had a noise inspection call out and also had special size/precision callouts for "matching" and/or selective fitting at OEM build. They are NOT generic versions of the bearing part number that is shown on some of the bearing seals that some people try to use/sell.

You could take a 7207CTYDULP4 (high speed), 7207CTYDUMP4P4 (general purpose) or 7207CTYDUHP4 (heavy milling/grunt work) NSK bearing and replace the OEM bearings with these.

These are ABEC7 grade machine tool bearings that easily meed or exceed the OEM bearing specs for accuracy. However, they are not sealed like the factory bearings so you might want/need to add an external seal to the spindle nose. And, they are expen$ive.

However, you'll still need to regrind the spindle ID afterwards to make the tool axis run concentric with the true axis established by the new bearings. Anybody who merely installs new bearings in a spindle and doesn't regrind the ID afterwards is not doing a proper spindle rebuild in my opinion.

I saw the Hardinge spindle repair operation in-person a number of years ago before they bought BPT and it is first class.

Pricey??? yes.

Definitely "filet mignon" and not hamburger.

[machintek]

BTW, all S1STD spindles that I have seen have no seals in the bearings. There is an oil cup on the head where the oil follows a pipe cleaner to the felt strainer on the top of the quill where it drips through and onto the spindle bearings.

George

[NC Cams]

Hmmmm. Something must have changed but that is probably more normal than not considering what the oem BPT mill product has been thru over the years.

The bearing drawings I have are reliably that of an OEM quality bearing design. The spindle bearings of the typical BPT mill (which I thought we were discussing) were a reworked, sealed 6207 bearings. Reworked in that they were modified for preload, size qualified, etc as mentioned earlier.

Properly greased ABEC 7 bearings like those stated in the original post should work fine (use the "DUM's" for general purpose mill work). I"d be inclined to NOT allow oil to drip into them.

Why? When properly greased with a good, long life synthetic grease, the bearings should perform for hundreds of hours without the need for relube.

In fact, grease contamination is one of the major reasons for bearing failures - even more so than fatigue. Dragging contaminated lube in from elsewhere in the machine or operating environment is always a risk when one adds oil from the outside unless proper care is taken.