how much bigger does a drill bit drill?

Rcdizy

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If I want to drill a hole in stainless, and press fit a 3/16, O1 drill rod (.1875) into it....

What drill size? numbered, lettered, decimal?
 
Drills do not make holes to an accurate size. Drills do not make round holes. Drills do not make straight holes. All that said, the #13 might do it for you, depending. It also might end up too tight, or might possibly end up loose, depending... A drill one size smaller, #14, followed by an appropriate reamer for the desired press fit, would make for a lot less guesswork and a lot more confidence in a good outcome. You should also carefully measure the O-1 rod diameter with a trusted micrometer or compare it with a 3/16" dowel pin. O1 is usually within .001" of nominal size, but is definitely worth checking, especially at the end of the rod. Check it at several clock positions, too. In a hole of that small size, there is less room for tolerance stack up if you want a specific fit.
 
The #13 was too loose still, Size smaller too tight.

The rod is excactly .1875

So in a perfect world, what reamer?

Would locktight work in this type of application?
 
I would bore it. Right size, straight walls and you can decide the tolerances for the press fit.
 
In my experience, drill rod is often slightly smaller than nominal size. How much oversize a drilled hole is depends a lot on the condition of the drill. +1 on the undersized hole followed with a reamer. The size depends on the class of fit you require. Are you going for a tight slip fit, light press fit, or heavy press fit?
 
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