Do center drills have runout ?

It may be "off base" here, but way back I was given to understand that a center drill held in the tailstock against rotating work would "self center". This from an old timer in the plant machine shop who seemed to me to be on point. The theory I have held for many years is that the finished center cavity may be slightly oversized but true to the center of rotation. This is based on the rigidity of a short drill cutting to the side as the work rotates. With an oversized center hole, a center device will find and hold the center of rotation to get true work.

Sorry, I don't know the terminology for some of the points I'm trying to make. Hence there are too many "centers" here to make sense. Perhaps I don't have my caffeine level up to snuff yet. I don't do enough precision work to half, or less, thou to know if the thought is valid. At the level I usually work, it seems to pay off. The theory as explained to me makes sense and I don't worry about concentricity of my center drills. I will concede that most of my work involves small drills. My large size is only 1/4 inch / 6mm diameter for thr body. I have larger center drills but they are so seldom used that I don't consider them. Like the letter size drills, they aren't allowed to get rusty, but could easily do so.

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I take it this is like a regular drill ground with the point not on center. It will drill a bigger hole. Since a center drill is not normally used for precision, they may be within their designed tolerances. The biggest issue I see is one side will wear, and take more of the cutting then the other. Used on a lathe, as long as the tail stock is centered, the resulting hole will still be centered. Only have a bigger hole.
 
Your second video confirms what you showed in the first video: namely that the tip has a .1mm runout with respect to the shank of the drill. I would toss it as it serves no useful purpose. This could very well be the cause of your slanted holes. Try again with a good center drill and see if it makes a difference. Let us know what happens.
 
+1
Thanks for showing your testing. Do you have other center drills? Do you have some split-point drills? This makes me want to check some of mine to see how they fare.
 
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