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Grant's 077 bearing report

January 5, 2006
reference Jan 4th log

Wednesday 1/4/06 we found one shaft had been severely damaged by the needle bearing on the end. When I got it home and contemplated the situation, it became clear that the needle bearing had worn the shaft down from .3285" original diameter to .249", yet the machine still had the audacity to at least spin the rollers for a few minutes! Bob has suspected that the oilite porous bronze bearings were heating and gumming up. I think this is also a likely problem but it also became clear that fixing the badly worn shaft might be more important.

I've measured up the shaft and determined that the needed needle bearing is .3285" id x .561 od x .500 width. For the bearing conversant that think metric, let me save you the effort of calculating - .3285 is 8.344 mm, a definite oops. Or perhaps it is an odd inch fractional size - another oops at 21.024/64". My searching of Torrington, Timken, MRC and NTN web catalogs yielded nothing. The IBM original bearing is marked "Torrington NB-3 patented USA". My search leads me to believe that NB-3 means "Needle Bearing #3", like the third one ever made, leading to further speculation about how old Bob really is :-) .

Two of the three center journals on the shaft show light scoring wear but measure .500". The third measures between .4995 and .4987, which is not enough to worry about. All four card rollers seem perfectly round and measure 1.194". So, except for the one bearing failure this shaft is in much better shape than the one I reworked for the 1402 punch.

I happened to run into a couple of machinist friends and we figured out a way to restore the shaft by turning the shaft end to .249 and sleeving it back to .3285." However, doing this with a hardened sleeve that has a right sized taper pin hole in the right place is worth extra points in the annual impress your friends machinist contest. Needle bearings like to run on shafts hardened to Rockwell 58C or so - very hard. Taper pin reamers instantly go "snap" in steel this hard. So, not finding a replacement needle bearing is a blessing is disguise and permits me to propose a part I can make, an oilite bearing of the right size that runs ok on an unhardened sleeve. It won't last as long as a well maintained needle bearing but should be good for at least a thousand hours, which makes the next repair not worth worrying about.

I've poked around a bit on the web looking for info on restoration, re-lubricating, etc oilite bearings but not found anything as yet. "Vacuum impregnated turbine oil" is mentioned as the lubricant and the oilite is about 25% pores in the standard grade we would use and likely the only grade circa 1940's, although turbine oil was somewhat scarce then. So, a solvent soak, maybe ultrasonically, followed by thorough drying, best in a vacuum, followed by vacuum oil impregnation might remove gum and add oil. The 6 or so oilite bearings I measured while Bob was taking the machine apart all measured very near to their shaft diameters, which is quite good news.

One design mystery for the shaft I have is how it is axially located as all of the bearings are sleeves or needles, no thrust bearings I'm aware of. The drive gear is straight cut, so it doesn't provide an axial reference or preload either.

I'll order some oilite stock and hopefully will have time to make the sleeve and replacement bearings by 1/25. I won't be at the 1/11 work day.

Any better ideas for a fix or thoughts on resuscitation of the other oilite bearings would be welcomed. I'll take a few photos and send them to Ed for posting.

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