Origin of bearing fits
Origin of bearing fits
(OP)
The hole fits in ball bearings are not in line with the ISO fit system, beacause the tolerance of the hole is always pointed outside of the material. What is the reason for that?
Thank you in advance for your input.
Thank you in advance for your input.





RE: Origin of bearing fits
RE: Origin of bearing fits
http://www.fltpolska.pl/pl/produkty/26-flt_toleran...
RE: Origin of bearing fits
ISO does cover all the possibilities.
http://www.skf.com/binary/109-124478/Fig-17_tcm_12...
RE: Origin of bearing fits
On the other hand, ISO tolerance would typicaly be in minus material, e.g. 30H5=30+0.009
If we now examine different ISO tolerances trying to express the bearing's tolerance with ISO, we may find:
30Js5=30+0.0045-0.0045
30J5- does not exist
30K5=30+0.001-0.008
30M5=30-0.005-0.014
So, the best match would be 30K5, but it is not possible to express the bearing tolerance with ISO tolerance exactly. That leads to a conclusion, that some other tolerance system or rule must have been used. The question is, what was that?
Hope it is more clear now.
RE: Origin of bearing fits
RE: Origin of bearing fits
http://www.iso.org/iso/iso_catalogue/catalogue_tc/...
I think a slight broadening of the definition of "ISO tolerances" might help.
regards,
Dan T
RE: Origin of bearing fits
Metric bearing IDs typically are toleranced "opposite" inch bearings, but the desired resulting fits will be the same.
RE: Origin of bearing fits
This system is apparently not used for bearing bore standarization, as shown above. Other system(s) must have been used instead. The question is- why?
RE: Origin of bearing fits
Hi Spigor,
"Other system(s) must have been used instead. The question is- why? "
I think ISO 492 is where you should start. Not ISO 286. Or ISO 5775.
As to "why", I have no clues, let alone actual knowledge.
I find it is difficult many times just to correctly identify truly "what is" without even considering "why it is."
Per-Haps because the ABMA was founded 2 score years before ISO was even invented?
http://www.americanbearings.org/?page=bearing_time...
1917 – U.S. Bearing Manufacturers create an informal group to aid bearing manufacturing for World War I, which led to the founding of ABMA.
"http://www.iso.org/iso/about/the_iso_story.htm
In London, in 1946, 65 delegates from 25 countries meet to discuss the future of International Standardization. In 1947, ISO officially comes into existence with 67 technical committees (groups of experts focusing on a specific subject)."
And, ISO has aligned itself with the US and Japanese bearing manufacturers.
RE: Origin of bearing fits
I agree it's not very important why they do it this way as long as they end up with the same numbers, but I just find it interesting.
You said inch bearing bores are toleranced opposite the metric bearing bores. So the inch specs would be "correct", and the metric specs "opposite". That and the historical timeline might serve for an explonation of the inverted metrical system.
That, or it's all just an accident...
Thanks everybody for your input!
RE: Origin of bearing fits
1947 - 1917 = 30 not 40.
So 1.5 score, not 2 score.