[TR] Triumphs Digest, Vol 5, Issue 96

[Michael Marr]

>
> Yes, but that happens because a drill bit is normally working from a
> "center" at the tip.  Grind one lip longer than the other, and the point 
> is
> no longer in the middle of the drill (making it farther from the point to
> one flute).  Run that same drill bit through a pilot hole (so the tip of 
> the
> bit no longer engages the work) and it won't cut oversize.  Or at least 
> not
> nearly as much.  A properly sharpened drill bit does cut just a bit
> oversize.
>
If the effective radius of the cutting edge of the reamer changes around the 
circumference, which it will do if the new cutting edges are ground by hand, 
it will force it to cut more on one side than the other, with a reactive 
force greater on that side than the other, thus deflecting the reamer enough 
to cut oversize.  It doesn't need a point to make it walk - although I agree 
the effect is greater with a twist drill because the cutting edges are 
longer and there is more contact with the metal.  However, I agree that in 
the case of hand reaming, the effect is not noticeable.  Instead, I think 
you would just get a bad finish which, if you are going to secure the 
bushing with loctite, isn't really an issue as you point out.

Mike