Repairing a bearing shaft

[GaryK]

I repaired some shafts from the gearbox of a SB13 a while ago and just turned down the original shaft pressed some sleeves one.
Then turned it down to the correct diameter. Worked great.

From the picture of the bushing you get the idea that they really needed fixing.

 

[DMS]

Well, brazing was a no go. I had two torches (1 propane, 1 MAP) on it and after 20 minutes I managed to attach 1 glob of braze. I just can't generate enough heat unless I build some sort of oven out of fire bricks... and for that I need more fire bricks.

So lets talk about that sleeve. How thin can I get away with? I have about 0.160" total wall thickness on the shaft, and there is a key in it. I have attached a pic of what I am working with.

The large cone shaped piece is the one that needs repair. In this photo I have the piece pressed onto it's mating shaft (the end of which has the toothed pulley and dog clutch on the end) and mounted in the 4 jaw chuck of the monarch so that I could keep things concentric. When I took this picture, I had just finished cleaning up the surface.

Because the piece I am working on is pressed onto another shaft, it is hollow in the middle, so I don't have much material to remove... which is why I am wondering about minimum thickness on the sleeve.

In any case, I am going to grab some DOM tubing to try out. If anybody can advise me on minimum thickness, that would be appreciated. Currently the shaft is about 0.080" under size, so I am hoping that 0.040" wall thickness will do...

I also realized that this thing is going to be impossible to measure with a micrometer, so I need to make some go-no-go gauges? Or is there a simpler way?

 

[Tony Wells]

0.040 wall will be just fine. I'm not quite getting why you cannot work directly on the piece needing sleeved. Or even if you had to make a dummy shaft to run it on, a capture spud or something.

 

[DMS]

Here are a few more pictures to get an idea of the whole thing. The part I am working on is the lower pulley on the spindle side of the variable speed drive. It also serves as the brake drum for the spindle brake, and the "shaft" I am repairing supports the main bearing on this portion of the drive train.

The first pic shows the underside of the pulley, at this point I had turned down the shaft (maybe "boss" would be a better description?) to clean metal.

The second pic shows the shaft this piece mounts to. The bottom portion is a toothed pulley that runs the back gears. I had the pulley pressed on to this to hold it in the lathe.

The third pic shows the bearing and the piece the bearing fits inside. This whole assembly gets pressed onto the pulley, and then the pulley gets pressed onto the shaft in picture 2.

The fourth pic shows all the pieces as they go together.

 

[Syaminab]

@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...

He is using what we call size 80 tube, which is oversized to be driven in the shaft, then he remachines to final size. Size 80 means a seamless tube that holds 80 kg/cm2 pressure as working pressure.

 

[Tony Wells]

OK, I get the picture now. Since you have already trued up that surface, no need to remove more material. I see two options readily. One easier than the other. I'll describe the one I would probably do. If you can get an accurate measurement of that diameter, simply make a bushing to light press into the bearing bore, with a bit of 680 Loctite. This bushing would need to be an accurately sized piece that would light press onto the pulley also. You don't want to crush the pulley at all, so be careful with the measurements. Turn, bore and part off in a single chucking so you maintain concentricity.

The other method would be to bore a close fit sleeve for the pulley and again, close but no crush, Loctite it on and then machine it in place to fit the bearing. There is no need for a strong interference fit anywhere in this.

 

[DMS]

I think I will go for the second method you describe, as the datum that the bearing pushes against axially also needs truing up. I ordered some DOM tubing, and I'll see if I can track down some 680 loctite. I guess until then I'll figure out how I'm going to measure things with sufficient accuracy.

 

[swatson144]

Measurement is easy. Give it your best read and if you don't like the fit compensate and make another. DOM is fairly inexpensive.

Usually you can come out right on just by averaging hard to measure areas if you don't have the exact measuring instrument needed. I'd find something nearly the same size and mic it then measure it with calipers and then measure the calipers. It looks like you may be able to fit a set of dial/digi calipers in there. If not just use a plain old fashioned set of friction calipers, just measure several times until you have a warm fuzzy feeling.

You are just looking for a very light press fit or even a snug slip fit. Just make sure the sleeve isn't warm when you test fit as it may get captive 1/2 way on. There isn't very much difference in size to a shrink fit. I did that sleeving a motor shaft "yep that seems about right...Aught oooh NO"

Steve

 

[DMS]

I realized this morning that I don't have to be dead on for the ID on the sleeve, because the loctite will take up the slack, but when I finish up the diameter for the bearing, I think I am going to need a light - medium press fit, correct? I'm thinking 0.0005-0.0010 over size on the boss. I can get calipers in there, but I don't trust them to that degree of accuracy. I was thinking that I can just leave the sleeve long while I turn it, so I have something to measure, and then once I have the diameter right, face to length.

 

[DMS]

Machined the sleeve, turned up an mandrel, and the sleeve is mounted with the adhesive drying. It's about 1" oversize on the length so I can have something to measure. I'll try to finish it up tomorrow.