Originally Posted by
chuK_138
NSK bearings are Japanese, unless you're buying knock-offs. I just inspected a 62 last week that had a problem and it ended up being a busted shield and marked MADE IN CHINA. The measurement with the wire means you would lay two pieces, one on each side of the groove the caliper jaws will touch, to get the overall diameter of said pulley. Don't know who made the rule, just know it as a machinist student.
Do not read if you want to complain of the waste of time later.
There will be a test later.
You are partially correct, I was looking for the explanation of the 3mm wires. The 3mm size is wrong, it is much to big and would sit on or near the radius at the top of the 40 degree form.
The wire used will sit on the flanks of the form. The wire used could give the pulley diameter directly, but the wire would be a certain diameter.
Normal practice is to use wires a little larger so that the calipers or micrometer is measuring above the pulley diameter so no interference arises from the form either side of the wires. You would be machining down to a dimension which would be greater than the pulley diameter, that dimension would only be true when the actual pulley diameter had been reached.
The difference between the pulley diameter and the calculated dimension would be used as a constant to make any pulley diameter.
Using this figure you could calculate the true pulley diameter as opposed to the advertised pulley diameter. Measuring an actual pulley does not give the true working diameter, the rads at the top change the actual diameter, big rads = smaller measurement, small rads = larger measurement.