On my much less diameter (2.000") I just used a spotting "bar" that was actual size of journal during scraping. The bearing is adjustable via a solid phenolic "wedge" and the fitting involved seeing that it ran without heating much It warms up to the touch promptly and does not go higher. This is with a drip supply of Mobil Velocite #6, a very light spindle oil
In other words there is no measurable "clearance"
Thumbnail illustrates performance of this 1947 OD grinder
John, to clarify, the spindle diameter is 1.250, the bearing surface is about 6" in length (guessing here, I don't have it handy).
On one that I use regularly, call it grinder #1, the surface finish has degraded to the point it is not usable. Speaking with my spindle guy (who does not work with plain bearings) he said I should have MAX .0002" play in the spindle. I can currently push the spindle down about .0004", I can pick the spindle up .0035". If I tighten the bearing up further, it heats up FAST and continues to get hotter.
On the other (grinder #2) that I use for roughing and general work, I can pick the spindle up about .0021, and push the spindle down about .0004. I get good surface finishes with this machine, though if I take a heavy cut, or the material is hard I do get a bit of wavy ness if the wheel isn't open and sharp. This machine warms up quick to about 104 and stays there.
These numbers are with a cold spindle that was rotated by hand to distribute some oil.
So then we have grinder #3, which I have been rebuilding. Now that grinder # 1 is basically inoperable, I need to get #3 finished. Or I need to rebuild the spindle on #1 since it is otherwise a good machine.
In regards to the ID of the bearing surfaces, on grinder #3, there are no remaining scrape marks, and it was a good running machine with good finish. Until it fell over when a friend was hauling it. So that leads me to wonder, if I shouldn't chrome the spindle, grind to .001 over and rescrape the ID of the bearing? Given the length, and the small opening, that would be quite a chore.
Sorry, replies faster than I can type!
Machinery's handbook has a whole section on bearing clearances. As I recall, it's a function of diameter, load, speed etc. Not at all straightforward unless you have all the necessary information.
I will check Machinery's Handbook, an old one!
A true Plain Bearing being a shaft spinning in some form of bushing perhaps babbet or bronze might have .001 .002 to the OD clearance when cold..depending on diameter perhaps up to 6" (?), and may have an end play nut adjustment.Heat rise is often the gauge. Guess I would bring to just zero end play and run it to see a little heat at 10 minuets warm up..getting hot=back off.
Other bearings ball roller and the like are often good with just bringing them up to zero end play and let the warm up make them tight. Finding a little heat at 10 minuets is good, with the spindle not getting hot to the hand touch after a half hour..
Good to state the grinder brand and a PM guy may have the specs.
*You can count your threads and know what a 1/16" turn would equal in thousandths.
just thinking that might be about .0002 or so.
Duplex bearings make their own pre-load up to a point as to a certain RPM and load range with just being tight together as specified direction..
These are Abrasive 1 1/2 machines, 1930-1940 vintage as best I can tell.
I went ahead and pulled the front bearing from #3 that in the spindle parts bin, it is 5 3/4" long, and the thread to tighten is 10 pitch.
I have a few minutes, I will do some experimenting.