# How To Repair Bushings & Pulley Bores



## JPMacG (Feb 27, 2016)

I had to remove the 3/4 inch countershaft on my Craftsman lathe.  This turned out to be no easy job.  

 I now have a pulley with a scored bore.  I also have scored brass bushings on the countershaft support bracket.  This happened as I pressed the shaft out of the pulley and bushings.   The shaft had a lump from the set screws that held on the pulley and collar.

How can I clean up the pulley bore and bushings?   Do 3/4 inch hones exist?   Should I use a 3/4 inch reamer?   Should I try emery paper wrapped on a wooden dowel?


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## Andre (Feb 27, 2016)

If it's light scoring, just make sure there are no burrs and reassemble. If it's scored to the point of being loose on the shaft, you must enlarge the hole then turn a sleeve and press fit and/or locktite it in place. This sleeve will have a bore the same size as your shaft and the same outside diameter as the enlarged hole in the pulley.

Make sure you remove that setscrew mark on the shaft, and maybe even file a small flat where the setscrew rests to prevent raised marks in the future. Help the next guy along.


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## TLW (Feb 27, 2016)

+1 what Andre said
   But if the bushings are scored or worn to the point of concern I'd just replace them. You can polish off the shaft (an add the flat where the set screw rests), press in new bushings and reassemble. If you caught the issue in time and the bushings are not worn so much that the shaft is lose you should be in good shape. 
   You must have noticed a problem in the first place to want to remove the shaft so you might be in the same boat I am. I need to replace the two bushings and make a new shaft...No big deal really if you have the capabilities to cut the key-ways for the woodruff keys.


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## dlane (Feb 27, 2016)

Don't do that "no mo" !.


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## Rob (Feb 27, 2016)

All of the bushings that I have replaced on my 12" Crafstman lathe have been standard off the self bushings available at most hardware stores. Just press the old ones out and then the new ones in. I have then used a sharp reamer to size.


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## JPMacG (Feb 28, 2016)

Rob, Do you ream the new bushing by hand?   Or do you fixture the part and ream it on a machine?


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## JPMacG (Feb 28, 2016)

Thanks everyone.   Now that I have cleaned the parts, the damage does not appear to be as bad as I first thought.   I may be able to deburr the shaft with a file and fit it all back together.  I will definitely add a flat for the set screw.

But on careful inspection I notice that the oil ports on the bushings don't go anywhere - there is no hole into the bushing.    Shouldn't there be a small hole from the oil fitting into the bushing?  I wonder if a previous owner has already replaced the bushings but didn't add the hole.


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## wa5cab (Feb 28, 2016)

Most people seem to make the assumption that the oil cup hole should line up with a hole through the bushings.  But all of the bushings that Atlas used (except maybe those where grease cups are present) are of the sintered bronze type commonly know as "oilite".  The bushings themselves are porous and don't need a hole added to let the oil through.


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## JPMacG (Feb 28, 2016)

Ahhh.... clever.   Thank you Robert.


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## Steve Shannon (Feb 28, 2016)

I have a question about Oilite type bushings.  I've only ever seen them fitted by interference along their OD, so that they don't move with respect to whatever they are inserted into.  Is is possible instead to press fit them and perhaps even loctite them onto the shaft at their ID, so that the bearing surface is the outside sUrface (OD) of the Oilite bushing? Why not?


 Steve Shannon, P.E.


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## T Bredehoft (Feb 28, 2016)

If you compare the area of surface between inside and out you will find the inside to be much smaller, less friction. That's why bushings are stationary relative to the shafts inside them.


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## Steve Shannon (Feb 28, 2016)

Thanks. I was thinking that because of the increase in surface area that the normal force would be decreased and area of lubrication would be increased, so friction would be reduced. 


 Steve Shannon


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## Steve Shannon (Feb 28, 2016)

After considering this more and some Google research, I remember that the calculation for friction force is only affected by normal force and coefficient of, not area. So I believe my question is still unanswered. 


 Steve Shannon


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## Rob (Feb 28, 2016)

JPMacG said:


> Rob, Do you ream the new bushing by hand?   Or do you fixture the part and ream it on a machine?



Mostly by hand and with a sharp reamer and minimum turns of the reamer. If I do it in the lathe I still turn it by hand if possible.


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## wa5cab (Feb 28, 2016)

Steve,

I don't see any particular physical reason why the bushings couldn't be a press fit on the shaft and turn in the bore.  But there is probably a sound financial reason not to do it.  In practically all cases, the cost of a replacement shaft is much less than the cost of the housing.


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## Steve Shannon (Feb 29, 2016)

That makes sense. Thanks!


 Steve Shannon


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## Round in circles (Feb 29, 2016)

Steve Shannon said:


> After considering this more and some Google research, I remember that the calculation for friction force is only affected by normal force and coefficient of, not area. So I believe my question is still unanswered.
> 
> 
> Steve Shannon


Cor that stirred the old grey matter in the bone dome..


IIRC ............................  ro x mu x surface area = coefficient of of friction   ( aka drag resistance ) ... so I suspect that yes surface area will have some effect .
 The other thing that makes a big difference is the viscosity of the lubricant and its rate of decline as a lubricant etc , get it right in the correct tolerance fit and the shaft actually rotates / floats inside the bearing on a film of oil .


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## Tony Wells (Feb 29, 2016)

In the likely event of a lubricant film failure, the probability of survival is much greater using a steel shaft in a fixed bushing vs a bronze shaft (essentially) running in a cast iron piece.


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## Steve Shannon (Feb 29, 2016)

That equation is not familiar to me. mu is typically used to represent the coefficient of friction (empirically determined as I recall) or a drag coefficient in aerodynamics related to shape. Rho is typically used in fluid dynamics to denote fluid density. Do you have more info about how your equation is used? Thanks!



 Steve Shannon, P.E.


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## Steve Shannon (Feb 29, 2016)

Tony Wells said:


> In the likely event of a lubricant film failure, the probability of survival is much greater using a steel shaft in a fixed bushing vs a bronze shaft (essentially) running in a cast iron piece.


What about a steel sleeve, pressed onto the steel shaft, which would run inside the cast iron piece? The actual application is the shaft within a backgear for a lathe. The replacement backgear has a bore that is 50 thousandths of an inch larger than the existing eccentric shaft. 


 Steve Shannon, P.E.


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## Tony Wells (Feb 29, 2016)

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.


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## Steve Shannon (Feb 29, 2016)

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


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## Tony Wells (Feb 29, 2016)

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.


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## Steve Shannon (Feb 29, 2016)

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.


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## wa5cab (Mar 1, 2016)

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.


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## Steve Shannon (Mar 1, 2016)

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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## wa5cab (Mar 2, 2016)

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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