How To Repair Bushings & Pulley Bores

If I were doing it, and this gear was intended to free float on that shaft, I'd bore it larger and put a Oilite bushing in. It would be easily serviceable in the future that way, whereas a direct fit would wear the gear and require more difficult future repair.
 
That's really what I would like to do, but I wasn't confident in my ability to bore the gear and somewhere I read that with lubricant cast iron on steel wasn't bad.


Steve Shannon
 
Many applications are found where there is a simple interface of steel/cast iron. So yes, it can be done. I was merely suggesting a better alternative. Most places where there is no sacrificial component found are rather antiquated, or the design decision is based on predicted lifespan. If this was a static, non-load bearing application, I would have no problem using steel in cast.
 
Thanks, Tony. I like your suggestion and may do it. First I have to finish the shop, then put the spindle back into the headstock, and then, finally, I may feel courageous enough to attempt to bore the gear and press in a bushing.


Steve Shannon, P.E.
 
Steve,

The back gears on all Atlas built lathes have two sintered bronze bushings pressed into either the sleeve or the gear assembly depending upon model.
 
You must have seen one of my posts where I mentioned my 6 inch Atlas. This is for my Jet 1336 PBD project lathe. The original back gears were steel and had bushings. They and the bullgear each had a broken tooth and a very tight chuck, which I suspect was the reason for the broken teeth. I got the chuck off, and am now in the process of replacing the bearings. I don't want to hijack this thread with that project, especially when I already have a thread going for that lathe in the Jet forum. Parts for this Taiwanese built lathe are no longer available from Jet, but the backgears and bullgear appeared to be nearly identical to the analogous parts in the Chinese manufactured BDB-1340, which is in current production, so I took a chance and ordered them. The chance paid off, mostly, but the backgear is cast iron, rather than steel, has no bushings, and . Bushings are not shown for the backgear in the BDB-1340 parts list and the bore is about 50 thousandths larger in diameter than the Taiwanese built shaft, which is too small (correct me if I'm wrong please) for a bushing. The gears are helical, or I might have had them welded/grazed. Because of the eccentric shaft for the backgear I cannot turn down the journal; a step would be formed which would inhibit sliding the shaft into the backgear. So, I was hoping I could pass fit a sleeve onto the shaft and then turn that down to fit the new backgear without having to turn the backgear bore. The sleeved shaft could possibly be turned in my Atlas.
Sorry for the overly long post. Thanks for your interest!


Steve Shannon, P.E.
 
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0.025" wall thickness is pretty thin for a sintered bronze bushing. Plus although they work quite well in being press fitted into a bore, I would question whether the tensile strength of sintered bronze in tension instead of compression would be adequate for an application that required such a thin section. You might get away with it if you use solid brass or bronze and are consistent about oiling it every half hour or so of operation in back gear. I assume that there is an oil hole and plug in the hollow sleeve that connects the two back gears. In any case, I would try that before going with steel.

But the best solution if you can do it would be to bore the substitute back gear assembly through and through for sintered bronze bushings.
 
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