Lots of good advice in this thread!!
Regarding the original theme:
It indicates the centerdrill is below the spindle centerline.
It is a number of factors that add up to being below or off center
This is surprisingly common. My Leblond lathe was manufactured with the tailstock being .003 above centre line, in order to accommodate wearing in of the veeway and flatway. After 40 years, it still is about .0025 high. I just compensate for that with a boring head when needing a dead centre.
Yes, one day, when I need a new project (number 4005 or so) then I'll scrape in the tailstock to be .0005 high.
----------
Now concerning the idea of drilling, and deviation: like anyone with experience, the answer is: It depends. A normal length inexpensive 2 flute drill will never cut a 'rubbing' hole, but will cut several thousandths oversize. This is partly because of imprecise sharpening of the two flutes - but even if the flutes are perfect, there is still a tendency to wander at some angle a little bit. The extra space will allow the drill to find its own direction somewhat, resulting in a hole that isn't perfect to the centreline.
Starting a hole with a spot drill, and then a short series drill (which is far more rigid) can easily help this situation. While a spiral drill will never be as straight as a high-pressure gun drill with ground inserts, it is possible to drill a 1/4" hole 6" with less than .015 deviation. I have done this many times.
If you *must* have a straight DEEP hole to a tight tolerance, then you have to drill a hole undersized to around 3-4Xdiameter, then bore it to size or slightly undersized, then peck drill with a short series CARBIDE drill, then you can follow up with a regular sized drill. this 'pilot' hole will serve as a stiffener for the drill bit, and help get the hole straight. NOTE. this builds up heat, even with good lubrication, so regular extraction of the full drill bit and flood coolant are essential to not breaking your drill. I have had over 95% success in 20X+ deep holes.
Why Joe is right: he insists on using a centre drill to start his holes - nothing wrong with that, if you don't mind your hole starting just a tiny bit off centre. even a .001 deviation will help get the angle wrong. But by drilling holes Joe's way, I'm afraid you have to expect Joe's result.
Anyone, even a beginner, can do better than what Joe is proposing by following the above suggestions.
