VN How To Proceed With #12 Head Cleaning?

Jeff,

I reached out to one of my mentors, a master machinist and mechanical engineer who is very skilled in machine tool repair. He suggested heating the cutter-head up to about 150 degrees for a day and applying a penetrant like Kroil to the bearing/spindle interface. Then let it cool overnight and press the spindle out of the bearing. He doesn't think you will damage the bearing by doing this.

I know that I've seen the Timken bearing load tables somewhere, but I can't seem to find them now. You might try the NSK or SKF tech data for bearings of that size, if you can't find Timken's data. If you find the tables, please let me know where.

If you have a large enough arbor press, that would probably be the way to go, since you'll have a better feel for what's happening to the bearing.

Cal
 
Hi Jeff,

Thanks for the link!

I would guess that the cup is 28300, which has a 3.0000" OD; at least that's the OD of the rear bearing in my No. 16 (which uses 2780/2720 for the rear spindle bearing.) You drawing shows Ca90=3000 lbf. So a ton of axial force should be well within limits. Put a pressure gauge on a bottle jack and (knowing the diameter of the cylinder) you can calculate the maximum gauge pressure to stay within limits.

Cal
 
Hi Jeff,

I passed the specs on to my mentor and he thinks that 5 tons force is no problem. He's confident that the bearing will move long before you reach that level.

Cal
 
Thanks Cal:

I actually got some conflicting information from a bearing expert... a friend of my father who was the tool room foreman and a master machinist for the Barden Bearing Company for almost 50 years and just recently retired. He told me that roller bearings (and also angular contact ball bearing sets) should be firmly preloaded in spindle applications, especially in relatively slow speed spindles such as used in the VN head. When he moved the spindle by hand (with the head off of the ram) he did not think that the preload was excessive. We ran the mill for about 15 minutes and made some pretty nice looking cuts. The top and bottom areas of the head were noticeably warmer than the mid-section which concerned me, but my friend was unswayed in his opinion that the preload was fine. Pointing to the specs, he showed me that the upper bearing was rated for 1 million revolutions with 8 tons of radial load, so why was I worrying that it felt a little stiff to turn by hand? I guess I can see his point.

I may still take everything apart anyway for a different reason. I've noticed more old grease coming out of the bearings along with new grease, so I did not get all the old junk out the first time. I washed the lower (front) bearing out with flowing kerosene before you told me about the set-screw and collar covering the lower bearing, so I obviously didn't do a thorough enough job. I'll also switch from the urea based grease I used the first time to the Mobilith SHC grease you suggested as it seems to be better suited to the application.

I won't have any time to play for the next week or so, but I'll post again after I try something.

Thanks again... Jeff
 
Hi Jeff,

The bearing end clearance numbers that I gave you came from Van Norman information that I have.

I'll see what my machine tool mentor thinks about the question.

Cal
 
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