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Drilling Problem Solving
There are many problems that can occur when drilling. Today we will discuss some of the most common problems. We will cover oversized holes, short tool life, rough finishes, chipped cutting edges, and the drill walking. We will begin with a few tips on drilling.
A drill removes 100% of its diameter making them one of the hardest working cutting tools. It is best to use a drill with the shortest overall length available that will work for your application. This will keep run-out to a minimum and help maximize the tool life. Standard drills (non-coolant fed drills) are best for making holes up to 3 times the tool diameter deep. In other words a 0.125” diameter drill should drill no deeper than 0.375”. If your application calls for a deeper hole then a coolant fed drill should be used. Spotting drills should be used to aid in putting the hole in the correct location. A spotting drill’s point angle should be greater than the production drill’s point angle. This helps prevent edge chipping and accurately locates the hole on your workpiece.
Oversized Holes
Oversized holes can be caused by too much lip relief, unequal lip heights and a worn drill bushing. Below are possible solutions to each of the causes.
| Causes | Solutions |
| Worn Drill bushing | Replace drill bushing |
| Unequal lip heights | Regrind drill with equal lip heights and chisel in center |
| Too much lip relief | Reduce lip relief to provide smaller chisel angle |
Short Tool Life
Short tool life can be caused by the fact that only one lip on the drill is cutting or drill dwelling. Below are possible solutions to each of the causes.
| Causes | Solutions |
| Only one lip cutting | Regrind drill with equal lip heights and chisel in center |
| Drill dwelling | Maintain sufficient feed rate (see Drilling Speeds and Feeds) |
Rough Finish
A rough finish can be caused by a dull cutting edge or an insufficient amount of coolant. Below are possible solutions to each of the causes.
| Causes | Solutions |
| Insufficient amount of coolant | Maintain sufficient coolant flow (see Drilling with Coolant) and verify correct type of coolant is being used. |
| Dull cutting edge | Regrind drill point with fine grit diamond wheel |
Chipped Cutting Edges
Chipped cutting edges can be caused by any of the following: vibration, too much feed, thermal carbide cracking, or too much lip relief. Below are possible solutions to each of the causes.
| Causes | Solutions |
| Vibration | Replace a worn drill bushing. |
| Too much feed | Lower your feed rate (see Drilling Speeds and Feeds) |
| Thermal carbide cracking | Maintain sufficient coolant flow (see Drilling with Coolant). |
| Too much lip relief | Reduce lip relief to provide smaller chisel angle |
Drill Walks or Drifts
The drill walking can be caused by a worn drill bushing or unequal lip heights. Below are possible solutions to each of the causes.
| Causes | Solutions |
| Worn Drill bushing | Replace drill bushing |
| Unequal lip heights | Regrind drill with equal lip heights and chisel in center |
I’ve addressed some of the more common problems encountered while drilling but this post by no means addresses them all. We would like to here about some of your drilling experiences with exotic or hard to drill materials; or if you are having issues drilling please leave us a comment here on our blog or drop us a line on Super Tool’s Contact Us page. We are happy to help.
Bryan Enander
Super Tool, Inc.
941-751-9677