As I understand it, putting non-precision bearings in a lathe spindle will work, but will give a wandering runout of around 1-2 thousandths. That's what I have now.
Do I need precision bearings for my purposes? Nope
I sure do want them though...
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No, not one or two THOU. You should be able to get down to sub TWO TENTHS, even with very average rolling-element bearings. Not skateboard-wheel El Cheapos, but still....
50 millionths, 35 millionths..that was 10EE as of
1939.
By the mid-late 1960's LeBlond and Timken were in an advertising co-op program where they took, for example, the whole back cover of dead-tree magazine "American Machinist" about every second month - inside pages in the in-betwen months - to advertise a LeBlond with 25 millionths TIR spindle bearings.
Two-tenths or so is about all you can expect from the WORKHOLDING - good collets, for example.
So if you can get an old lathe to a "half tenth".. ten times worse than the "half of a 100 thousandth" that 50 millionths represents, you can easily, reliably, and often split ONE THOU in the work.. and a "half-thou" is all we really need, most any day, "if even" that fine.
Most work I did, plus 2 thou, minus zero, was about as tight a spec as we ever saw, and it was considered tight - not common.
The world is FULL of average stuff that isn't even that picky.
Shorter advice: Lathe spindles were built to use
available bearings that already existed. Not the other way around.
Ergo a decent bearing house should be able to help you get all the improvement you can realistically put to use. Collars, sleeves, shims? You may need to buy or have made. PM community is a resource for that. I am not he as is the expert but we have many here who surely
are.
US / European / Skandihooligan / Japanese.. even Chinese?
Doesn't make a damn.
ROLLING element bearings have been done to METRIC dimensions from Day Zero to present day.