What are your thoughts on sugested bearing seat mounting tolerences?

[fsincox]

I am interested in the your impressions/experience with the bearing manufactures recommend bearing seat machining tolerances like the ones from SKF referenced in the in this thread;
thread821-300114
Approximately midway in the thread is a link to an SKF chart of recommended bearing mounting tolerances for different grades of bearings. These are fairly similar to all the different manufactures I have seen.
I realize your applications make a difference; we actually use the highest grades as I work with machine tools spindles and aerospace applications. The chart for those is linked at the very end of their page.
We often do not achieve these tolerances and I am just looking for other impressions from people with similar experiences.
Thanks,
Frank

 

[MikeHalloran]

The few machine tool builders whom I have met are _really_ fussy about spindle bearing mounting. ... not because the machine will explode before shipment, but because a bearing fitted other than 'perfectly' (to a really fussy guy) will not achieve its design lifetime and may underperform in other ways. ... which may not show up as warranty claims, but will show up as bad word of mouth, for which there is no effective defense.

So, I have to ask why you're not meeting your own tolerances, and why you're presumably shipping such product?



Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

Which tolerances are you not able to meet?

Reaching the full catalog speed rating (heat generation) and meeting Ford, GM and Chrysler's spindle vibration specs was hard enough with seats actually done to those specs.

 

[fsincox]

The bore eccentricity was one of the hardest. My experience would tend to lead me in the same direction, we had spindle trouble. I am just trying to get a feel for what other's think and have expienced with these. These are not my tolerances; they are the manufacturer's recommendations. I really was wondering if users thought they were too conservative.
Thanks,
Frank

 

[MikeHalloran]

>>>...they are the manufacturer's recommendations. I really was wondering if users thought they were too conservative.<<<

For spindle bearings, no.

Mike Halloran
Pembroke Pines, FL, USA

 

[dinjin]

If you make both parts and can possibly sort and match the parts you could probably relax the tolerances Do resolve your eccentricity problems.

 

[Tmoose]

"we had spindle trouble."

Trouble = Noise, vibration, workpiece finish, operating temperature, bearing life, something else altogether?

How much out of tolerance was the eccentricity/co-linearity?
And, resulting axial runout of housing shoulders?
What size bearing?

Sometimes assembly methods can induce problems with well designed and manufactured parts. Although part of good design is easy assembly in my book.

 

[caoimhin1]

For high speed machine tool, I can't comment. For general industrial applications, most end users jaws drop when told what positional tolerances they need to hold. Despite what everyone says about positional tolerances being very important, in reality most industrial machine makers are unable hold what is required; either because their shaft/housing supplier (typically outsourced to China or India) are unable to hold the required tolerances or paying the premium to get the tolerances will make the components uncompetitive.

 

[fsincox]

caoimhin1,
That is my experiance, too. People can not believe we wanted those tolerances. I really had a feeling we just were out of date, our solution became buying our spindles from Setco.
Frank

 

[MikeHalloran]

>>>paying the premium to get the tolerances will make the components uncompetitive.<<<

Only in the bizarro world of supply chain professionals do cheap components that don't meet the specification compete with components that meet the specification but cost 'more'.



Mike Halloran
Pembroke Pines, FL, USA