Jobber Drills, Stub Drills, Spot Drills, and Center Drills Understanding the Difference

[Geoffrey Less]

When it comes to machining with drill bits, the number of options can sometimes be a little overwhelming. If you have to deal with the confusion of knowing when to use each type of drill, we are here to help. Knowing the difference between a jobber drill and a stub drill or a spot drill and a center drill can make a huge difference when it comes to how they will perform.

Jobber Drills
The most common drill bit is the jobber drill. This is what most people imagine when you bring up the phrase drill bit. These twist bits are most commonly used on softer materials such as wood, but they can also be used on harder materials when deep holes have to be drilled. The biggest issue with the use of jobber length bits is the fact that they can “walk” off target. This is a result of their length and the fact that high speed machining causes tools to oscillate drift off of their mark.

Stub Drills
In order to deal with the issue of drill bits walking off their mark, the stub drill was developed. These shorter drill bits are shorter than jobber drills, but they feature a similar twisted flute design. The shorter length makes them a far more stable option for drilling shallow holes in your workpieces.

Spot Drills
Another way to combat drill bits walking off their mark is to spot your drilling positions ahead of time. Spot drills are extremely short and their cutting surface is limited to their point. Instead of being used to create holes in a workpiece, spot drills are designed to create a small dimple to mark the location where a hole will be drilled. This small dimple makes it easier for longer drill bits to find their mark, so long as the angle of the spot drill’s point is equal to or greater than the angle of the twist bit’s point.

Center Drills
Often confused with spot drills, center drills are actually designed to mark the center point for a lathe. Some operators will try to use center drills to spot locations for drilling with a twist bit, but the point angle on a center drill is usually smaller than the point angle of a twist bit. This difference in angle can lead to drill bits deflecting away from the center drilled position due to the tip not seating properly.

If you are looking for high quality drill bits for your shop, Online Carbide offers plenty of high quality solid carbide drill bits. Their tools are manufactured from high quality tool carbide stock and they offer their tools at amazing manufacturer direct prices. Their catalogue includes jobber drills, stub drills, spots drills, center drills and a wide range of end mills. If you have any questions about the products they carry, feel free to reach out to a member of the Online Carbide team by sending an email to [e-mail].