On Mon, 20 Oct 2008 18:24:46 -0700, "Michael Koblic"
wrote:
"Wild_Bill" wrote in message
...
You would find out that a caliper is very handy to have for checking
bearing sizes.
Many (most) ball bearings are all metric, but some applications use a
combination of metric and inch dimensions, with inch used as the I.D.
Generic (or used domestic brand) calipers are available for about $20,
even for generic digital. Most digital calipers switch between metric and
inch for instant conversions, and also can be reset to zero at any point
along the beam.
Dial calipers are generally either metric, or inch, although there are
some that indicate both on a single tool.
Shafts and housing openings are machined to sizes which are appropriate
for the desired type of fit for ball bearings, otherwise bearing sizes are
selected to fit existing parts.
I am not sure that I get your point. Are you saying that the tolerances on
bearings are so loose that one has to get a handful and go through them with
a caliper to find which matches your shaft?
Bearing tolerances are very tight measured in microns. Check out
http://www.ntnamerica.com/pdf/2200/tolrance.pdf to see.
Looking through McMaster-Carr web site there seems to be a wealth of both
metric and imperial shafts as well as bearings. In my simple mind one would
use a 5/8" ID bearing for a 5/8" OD shaft. The tolerances quoted are 0.0003"
(converted from metric) for the bearing ID and 0.003" for the OD shaft
(worst case).
I am puzzled why in the case of this particular piece of equipment there are
15 mm ID bearings supporting a 5/8" shaft (measured in the middle with
calipers). To me it implies a degree of machining to achieve a fit, but why?
I would imagine it was machined down to allow a shoulder to press the
bearing inner race against. Most applications with a rotating shaft
have a slip fit on the outer race and a press fit on the inner race.
Check out these sites for info on shaft and housing design and shaft
and housing fit.
http://www.ntnamerica.com/pdf/2200/shaftdes.pdf
http://www.ntnamerica.com/pdf/2200/brgfits.pdf
I would not suggest reusing the bearings. They're pretty cheap and
readily available and it's not worth the risk. I'm going from memory
but I think you stated this was a 6202Z? If so, it most likely has two
shields so you would need to order a 6202ZZ. The 6202Z is normally
stamped on the shield because the factory doesn't know if it will be
used in a single or double shield application. If you order with one Z
you will only get a single shield. Good luck.