Machinists are familiar with spot drills–they’re stub length and have little or no flutes. These little drills are designed to be extremely rigid so that they can precisely spot a hole for a twist drill. Maximum meat in the shank keeps them on target. The goal is use the spot drill to make a little dimple in the workpiece that keeps the twist drill from walking so that the hole winds up in the right place.
When Must I Use a Spot Drill?
Is a spot drill necessary every time an accurate hole is to be drilled? It’s purpose is to ensure the hole is accurately located. The short spot drill is very rigid, and the spotting motion is unlikely to deflect.
However, if you use a carbide drill, or a screw machine length drill, spotting is typically not needed. The carbide itself is so rigid compared to HSS that the drill will go where it is pointed. As a matter of fact, most manufacturers recommend against spotting either a carbide twist drill or an insertable drill because its easy to chip the carbide in the dimple.
Screw machine length twist drills are much shorter, so they’re less likely to flex as well. In general, you’ll save a lot of time if you can avoid spot drilling. Investing in a set of screw machine length twist drills is well worth it.
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Post time: Sep-30-2020