It’s not just oversize holes, the hole is at an angle
Poorly unevenly sharpened /angled cutting edges will also lend to holes wandering that's why a good centre point drill in a locked up tailstock ram is used to advance a hole for the first few mm.By angle do mean to the centre axis or just meandering? As you quiet rightly say theorectially it shouldn't happen. Drilling oversize is possible with a good size drill, unless your using a small drill and it's flexing a bit like Dynarod. They drill for oil that way. Saddam was stealing it from Kuwait (one place I haven't worked in) by drilling horizontally. That's possible. Cheap drill and not centred from the off. My cheapo Chinese drills are very much a mixed bag. Had some centre drills where the chamfer had been ground in reverse. Trying to explain to the seller was like Basil and Manuel. But not sure which one of us was Manuel in the end.
Some hadn't been hardened.....etc.
Hold the drill in the chuck and the part in a misaligned tailstock or badly set up tool post .Seems not but there's no other way to drill an out of straight hole in a part turning on axis. Not one I can think of anyway.
Might be of interest or not? But I was watching mrpete222 on Youtube and he was producing centre drill abors. During it he showed a snazzy holder where the centre drill just pushes in and locks. He admired it but made a different style himself. I liked it and decided to work out how to make it and made 2 different size ones. Turning the morse taper for them is a bit of ball ache using the topslide. But... Makes an easy time of centre drilling. Also made a wobble broach by mutilating an old lathe live centre as they're £400 or were.Poorly unevenly sharpened /angled cutting edges will also lend to holes wandering that's why a good centre point drill in a locked up tailstock ram is used to advance a hole for the first few mm.
Out of a nice grey & blue windowed presentation box of 0.5 to 15 mm in 0.5mm's HSS twist drills made in Turkey & sold in the likes of B&Q big box stores four of the smaller drills had been sharpened with the web of the drills justified to one side ... to almost 1/4 of the drill diameter
As soon as I discovered the 1.5 mm drill was off I checked the rest & reground all of the badly ground drills
Hold the drill in the chuck and the part in a misaligned tailstock or badly set up tool post .
Just going through my Chinese twist drills and bad news none will cut (even after attempted hardening) Slow speed steel?. The good news ......I've got lots of them.Poorly unevenly sharpened /angled cutting edges will also lend to holes wandering that's why a good centre point drill in a locked up tailstock ram is used to advance a hole for the first few mm.
Out of a nice grey & blue windowed presentation box of 0.5 to 15 mm in 0.5mm's HSS twist drills made in Turkey & sold in the likes of B&Q big box stores four of the smaller drills had been sharpened with the web of the drills justified to one side ... to almost 1/4 of the drill diameter
As soon as I discovered the 1.5 mm drill was off I checked the rest & reground all of the badly ground drills
That could drill a crooked hole but the part would not be turning on axis.