What is a Shaft Fillet Radius in a tapered bearing?

ebonfyre · May 2, 2018

I've been trying to find a rear wheel bearing for my IH 3514 and it seems to be a very scarce item. The manual calls for a part number ST2144 which is impossible to find at a reasonable price.

My research indicates the Timken 29681 is a modern replacement for ST2144. I have had limited success finding either of these parts. I did see however that the much more readily available Timken 29680 is identical in size, shape, and practically every other specification except for the ?Max Shaft Fillet Radius? dimension. I do not understand what the shaft fillet or it?s radius is to know how important this difference is.

Obviously I'm not going to put in a part that simply won't fit, but this is an old beater with plenty of hack-job modifications by past owners to keep her going and if this spec is not critical I'm fine with good enough if it means I can actually keep the tractor in service.

Does anyone know if this is an acceptable alternative or am I out of luck?

Oliver 500 Wa · May 2, 2018

Shaft fillet radius is the radius at the corner where the diameter that the bearing fits on and the face that locates it on the shaft or spindle.

You just need to make sure that the radius on your shaft is smaller than the value given for the bearing.

Roger in Iowa · May 2, 2018

See "R" on the bearing drawings above.

docmirror · May 2, 2018

Note the shaft fillet Radius on your axle is 3.5mm(0.14 in), and you want to put it on a bearing inner race with a smaller fillet radius of 1.3mm(0.05 in). The shaft will ride hard on the smaller radius and may crack the inner race when the axle gland nut is tightened.

This would mean, you are out of luck. HOWEVER; You can take the bearing, and the axle to any competent machinist and ask them to match the fillet, and they will grind the axle to match the fillet radius of the bearing race. (or grind the bearing fillet to match axle)

Alternately, you can hack-job it and just use a thin washer/shim of 70.637(2.781 in) on the face of the axle flange, and that will obviate the fillet radius. By doing this, you will reduce the strength of the axle at that contact point, because you are no longer matching the fillet radii of the bearing to the axle. It will be like having no fillet fit which reduces the chances for breakage. It'll work, but I would not put a whole ton of torque on the axle gland nut.

ss55 · May 3, 2018

I would compare the load ratings as well as the physical dimensions. It's not uncommon to find several load capacities with the same dimensions. If the tractor is still a working tractor you want to use a bearing with nearly the same rating as the original. Work through the bearing life calculations if you want to be sure.

If the tractor is a trailer queen or a collector tractor that will never see much work, then a lighter rated bearing could easily hold up for the remaining life of the tractor. Similar to when a Dupont overhaul is adequate for the job compared to an actual overhaul.

docmirror · May 3, 2018

(quoted from post at 05:44:49 05/03/18) I would compare the load ratings as well as the physical dimensions.

Co and C1 are identical.

ebonfyre · May 3, 2018

OK, much better understanding of this now, thank you all. I can't find any dimensional detail of the shaft online, but reasonably assuming the 3.5mm radius of the bearing part listed is a perfect match to the interior corner of the shaft, then yeah the bearing should touch at a single tangent point against that surface rather than be a snug fit. It's hard to visualize exactly how extreme the difference is, and I'm not opening that wheel up without parts handy so I think I'll look into buying the readily available and reasonably priced 29680 to better understand exactly how pronounced that radius is.

Oliver 500 Wa · May 3, 2018

The radius on the shaft and the radius on the bearing should not touch. The shaft radius should always be a bit smaller than the bearing radius.

What is a Shaft Fillet Radius in a tapered bearing?

ebonfyre

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Oliver 500 Wa

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Roger in Iowa

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docmirror

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ss55

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docmirror

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ebonfyre

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Oliver 500 Wa

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