Undercut between bearing seating and shaft shoulder

[cb68]

Hi

To aid manufacture of a shaft I am looking to put an undercut in the corner between the bearing seating and a shaft shoulder. The bearing is a 6000 series unit (ID 10mm, OD 26mm, width 8mm). The bearing has a radius of 0.3mm on its corner. Unfortunately all the bearing catalogues don't start providing undercut details until the bearing radius gets to 1mm.

Does anybody have a good rule of thumb or guidelines for the smaller bearings?

Thanks

 

[EdDanzer]

It will depend on the insert radius that is used to machine the shaft. If a ****432 insert is used for machining the undercut will be a plunge cut deep enough for some bearing radius clearance.

 

[diamondjim]

Why not modify the bore to have a camfer
or a larger radii? Why weaken the shaft
with an undercut?

 

[unclesyd]

The undercut if properly done want weaken the shaft and actually helps from the fatigue standpoint. We typically use a .75 mm (1/32&quot rounded bottom undercut. We keep the depth to a minimum. The undercut radius has to be tangent with the shoulder, no steps.

 

[EnglishMuffin]

The only strong reason to have an undercut is to prevent grinding wheel corner breakdown. I assume you are grinding the shaft, since you mention a bearing, and a pretty small one at that, so to achieve the necessary tolerances it would probably be essential to grind. If you want an accurate shoulder, the undercut should ideally be an angled type so that you have wheel clearance on both the shaft and shoulder surfaces. You can get away without a grinding relief on very small shafts, since the wheel stands up better, but if you do use an undercut, its more a case of what you can easily manufacture, rather than being something which the bearing companies need to dictate. On a bearing that size, as long as you have about a 1/16" wide land left on your shoulder you should be OK.

 

[rnd2]

I agree with Diamond Jim. Why weaken the shaft with an undercut????? Dumb and dumber.

 

[EdDanzer]

Actually having a larger radius undercut can lower stress more than a small radius if there is flexing under load at the radius.
Until FEA has been done don’t judge the design.

 

[EnglishMuffin]

EdDanzer is quite correct. But this is such an old thread that I expect cb68 has long ago made his decision, for better or worse.

 

[cb68]

Thanks for all your posts. EnglishMuffin was correct. I was looking to undercut the shaft to prevent grinding wheel corner breakdown. I ended up making the undercut angled with a width of 0.5mm and a tip radius of 0.2mm.