Repairing a bearing shaft

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DMS

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It has come time to make a permanent repair on my mill head (last discussed here [thread]3949[/thread]). I have the head disassembled as I make additional enhancements, including the addition of a spindle encoder and a switch-over from variable speed reeves drive (which is worn, no replacement parts available) to a fixed pulley belt drive.

The good news is that the JB weld has held up for over a year. Now I have to clean up the old repair to make room for the new one. I want to either build up the area with brazing rid and machine to size, or machine down, and press on a sleeve. I'd like some advice from the more experienced folks. The "shaft" is only about 50mm long, and 50mm in diameter. If I go with a sleeve, is that something I make myself? What material? Is it just a press fit, or do I braze/solder it on? If I build up the area with braze, how concerned do I need to be about distortion?

Oh yeah, the shaft is cast iron.

Thanks in advance.

Matt
 
Due to the small size of the shaft, I would try brazing the bad spot, then either machine it down, or maybe even just take it down with a file. If the bearing that slides on to the shaft is a good snug fit, brazing should hold up just fine, and I doubt that distortion would be a problem as you will not be getting the shaft as hot as you would with arc welding, not to mention that the heat of brazing will tend to affect a larger area, and over a longer period of time.

Sleeving the shaft may be the ideal solution, but may be overkill for this application. A sleeve could be made from DOM (Drawn Over Mandrel) tubing which would not have a weld joint running longitudinally down the tube. Sleeves like that are generally shrunk on by cooling the shaft and heating the sleeve, then pressing the two together. Once the temperature equalizes the two will be nearly inseparable.

One other thing to consider: if you braze first, sleeving is still an option later on down the road should your brazing repair not be sufficient.

Just my $.02 worth.
 
Thanks Terry.

I can't take any material down with a file, the shaft is recessed inside a larger piece, so material would have to be removed on the lathe or mill with a single point tool that can get in there. I only have small torches (2 propane units). I have done silver brazing with them; think they would be enough to braze with bronze filler?
 
Getting enough heat out of a small propane torch for brazing might be a little tough, but if the part is small enough it might just work, especially if you have managed to silver solder with those torches in the past. I guess there is only one way to find out, right?? :welding:

Machining inside that recess and getting the diameter correct may be a little difficult, but is certainly not impossible. Probably just have to sneak up on it. :scared:
 
I'll give it a try this afternoon. If I need more heat, I recall seeing something in an issue of HSM about building a charcoal brazier for this kind of work....
 
50 mm are over 2". I would go for the sleeve. A friend rebuilds the screws of Ice machines at waltmart, he uses sleeves he makes out of pipe and preses fit them with .005 interference. No heat, and when they are worn again, he just re machines to remove the old sleeve.
regards
 
I just made some sleeves for an old surface grinder I bought. I used oil impregnated bronze for the material in case you go that route. It's good where you have little or no oiling.
 
@Syaminab:

How thick is the wall of the sleeves your friend uses? The part I am working on doesn't have a lot of material to work with, I'm wondering how thin of a sleeve I could get away with. I'm gonna try to build up some material with braze metal because I have that in hand now (and now steel in the right size), but if that doesn't work, I'd like to have another option.

@Phils69:

This is a bearing shaft that accepts a 50mm ball bearing (6010 series) so I don't think oilite will work, at least I'd be too worried I would destroy it when I press the bearing on. I'll have to post some pics, the part in question is kind of an odd shape.


Gonna head into the shop and turn down to fresh metal, then I'll see how much heat I can generate...
 
Matt,

Repair of worn shafts is common in industry and there are ready made sleeves available. Check with your local bearing supplier and ask for shaft repair or shaft wear sleeves. They are simply a thin metal sleeve with a flange on one end and are driven onto the shaft with a tool (simply a collar that fits over the sleeve). Trying to heat a shaft that size enough to braze or silver solder it may do more harm than good.

Tom
 
It would seem that the best approach would be to disassemble the machine to get to the shaft itself with good access to the surface needing repair, then truing it up with the idea of putting a sleeve in place. You should leave the sleeve oversize on the OD until you have it in place securely, whatever means you use, then if at all possible, turn it true between centers back to proper size to fit an original bearing.
 
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