Do center drills have runout ?

[compact8]

I just checked three of my center drills with a dial indicator and all have big runout at the tip of magnitude 0.08 ~ 0.1 mm. Only the tip has this amount of runout. The amount seen at the main body of the drill is normal. Will it still do it's job ?

 

[mmcmdl]

Center drills usually don't have runout , spindles or collets/chucks do . The farther away from your holding device , the runout will be magnified .

 

[jwmelvin]

While a center drill may not have much warp or noncircularity, I think it’s appropriate to consider its runout when in a chuck, as you are doing. Dave’s point is that the observed runout likely doesn’t come from the center drill itself but rather the chuck or collet. If you see little runout at the drill near the chuck and more away from the chuck, the drill is not parallel with the chuck axis. I have a chuck with that problem, due to worn jaws. Not a lot you can do other than rebuild/replace the chuck. You can try inserting the drill fully into the chuck, as that can bridge the problematic area of a jaw.

 

[mmcmdl]

/\/\/\/\ Well said !

 

[Technical Ted]

Although I agree with the other posts before me (they most likely hit the nail right on the head), but if you have a cheap import tool, all bets are off IMO... Some import tooling is pretty rough in my experience. On the other hand, if you have a quality tool then I would say the way the tool is held in whatever you are using to measure it is the root cause.

Ted

 

[RJSakowski]

The proper way to test for runout of the tip would be in a V block. Otherwise you have to account for spindle runout and chuck runout.

Runout consists of two components, radial and angular. It is possible that a some point along the axis, they can cancel out giving a zero composite runout. As you move further away from that point, measured runout will increase.

 

[Nutfarmer]

Try using a collet to hold the center drill instead of a drill chuck.

 

[RJSakowski]

With a small center drill, the tip can flex slightly to start on an off center center punch. The main body of the center drill is much more rigid and will tend to follow the spindle axis. On very small end mills (.010 or .015" tips),this will usually snap the tip of the end mill but a slightly larger end mill could result in a center hole which isn't concentric with the larger diameter. If the larger diameter hole isn't deep enough to provide a guide for the following drill, it would have a tendency to start on the tip hole but as drilling progressed, the tendency to follow the spindle axis would become more pronounced and would result in drilling a hole on a slant.

When there is runout or spindle play, this tendency would become more pronounced as the tip is orbiting but once it makes contact, it will tend to start on the first contact point.. I have seen this behavior on a lathe where the drill is off center slightly and with small diameter carbide drills. It isn't unusual to have drills wander on the lathe resulting in holes that exit off the spindle axis.

 

[compact8]

Thanks for all the replies. Just to avoid any potential misunderstanding on what is seen. I have taken this video demonstrating the different amount of runout at the tip and the main body of the center drill. The diameter of the tip is 4mm, main body 10 mm.

 

[akjeff]

As someone pointed out earlier, measuring the runout with the center drill in a chuck, collet, or any other tool holder, you're not going to be able to tell what is causing the runout. The spindle, the chuck/collet, the center drill, a little of all of the above? Put the center drill in a v block and eliminate the other variables.