When holemaking goes awry, a chief problem can be runout, and you end up with a hole that’s larger than your drill’s diameter. It also means you might have just created scrap if the tolerance is unacceptable.
Are you measuring and watching for runout?
ISCAR holemaking guru David Vetrecin says that often machinists overlook runout.
“Minimizing tool runout and alignment is one of the most important criteria for successful holemaking because they affect process security, tool life, component quality, and surface finish,” Randy McEachern, a Sandvik Coromant product specialist, explains in the same Canadian Metalworking article. “Often we see uneven margin wear. In addition, the hole will be oversized and the finish can be coarse. In some cases, there will be a retraction swirl line in the hole.”
The culprit might be that your drill is running slightly off-axis.
Is this a challenge in your shop? Are you watching and checking for alignment—in drilling, in milling, in lathing? Which do you think is a better indicator: concentricity or total indicator runout (TIR)?
Here’s a solid write-up by Mahr’s George Schuetz on the two if you want a refresh on the difference.