liveaboard wrote: ↑Thu Mar 11, 2021 6:48 pm
Which makes me wonder;
Considering most of us simply don't ever work to such exacting standards, would a good quality normal tolerance bearing set do ok?
How much runout would one expect from modern regular high quality tapered roller bearings?
Maybe .002 to .003" ( .05-.07mm) ..which is common in Automotive bearings..
here is the problem fellows that you need to understand . I hear ---" I used cheap bearings and they had "0" runout "
Can that be real ? Yes
Will it always happen..? NO
You must understand how THEY make bearings to understand ----Why !
While
Bearing Makers grade the bearing components, it is the final assembly that "may " determine the quality ( Called "Grade" )
Please Know that a Roller bearing quality grade goes from 0 ( excellent ) to 5 ( Poor) - which is opposite of Ball bearing grades !
Lets say in this example , we have 3 parts, a roller, a inner race and a outer race ( 3 Parts)
So the Makers assembles the bearing and then measures it , and say it is TOO thick- even though the 3 parts were all a Perfect "0"
in inspection, the thickness downgrades it to Grade 3 bearing as that is the thickness that it matches.
Well, if you have Preload rings in the spindle housing that determine the preload, this is a bad bearing, but if you have a adjustable nut, The bearing even though it is a "3" is perfect in running !
So you can get a bearing that is prefect for your application- BUT If you want total assurance that the machine will work to your satisfaction, you have to make sure the bearing Grade is sufficient.
SO the Maker may put a perfect roller with less than perfect OD and ID Rings and the bearing is perfect ( a "0")
So the bearing maker makes 1000 bearings in a run- he would like them to be all superior but that is NOT the real world and he winds up with
75 Perfect bearings and those are "0" and then 100 that are 1's and 100 that are 3's and 725 that are 5"s for the total run
Then in final inspection they are stamped or marked and packaged as such .
So what really happens is THEY try to make perfect... and then mark them as they come out.
Try making a handfull of washers in your lathe ..make 20... some will be dead nuts and some will be too thick and some thinner /
Besides all this, don't forget, many precision bearings are "Matched" , so the Makers know they will be used as a "Pair" in the installation and they select the very best for this application -----the most perfect of the most perfect !
And know also that these 'precision bearings " will also have their High Points marked ( copper Dot) so eccentricities are known in installation.
So a bearing is not a bearing, it is an assembly of parts that go round and round and not all rounds are round !
Rich
Edit
You could say they all start out perfect and the rejects are culled out and sold as cheaper "Seconds"