Spot drills are compact tools that are easy to overlook, but they serve an important purpose in any machine shop. These little cutting tools are important for drilling holes with extreme accuracy, a task that can be difficult when milling.
What makes drilling such a risky procedure when it comes to milling is the potential for drill bits to deflect off of hard surfaces. Drill bits are relatively long compared to other milling cutters and that length comes with drawbacks. Long tools, especially those constructed from steel alloys like high speed steel, will naturally wobble while they spin. This can lead to them not hitting the surface of a workpiece at the optimal angle, which can deflect the point of the drill bit and ruin the cut.
Because milling is typically a very precise machining process, this can cause some serious problems. End mills and other cutting tools are more stable because of their width to length ratio, meaning this problem is almost only isolated to jobber length drill bits with a long flute length. Using carbide drill bits can help to minimize this issue due to their increased rigidity, but spot drills are another great way to produce accurate results.
Spot drills are short drill bits that usually just have a drill point and little to no flutes beyond that point. Their extremely short length makes them far more stable than longer twist bits. Instead of being designed to drill holes, these tools are intended to begin drilling to create a cone shaped dimple on the surface of a workpiece.
This depression helps to mark the location of hole you want to drill with your longer twist bit. Instead of deflecting off the surface, the point of your longer bit will be guided into the dimple created by your spot drill. The spotting process will greatly increase the accuracy of your holes.
In order to get the best results while spotting you need to consider a few things about your tools. If the point angle of your spot drill is not equal to or greater than that of your longer bit, you can still risk the bit deflecting on contact. This is a common issue when operators use a center drill in place of a spot drill. You should also consider your tool materials. You should spot drill when using steel drill bits but spotting may not be necessary when drill with carbide bits, especially of shorter lengths.
If you need some spot drills or some carbide drill bits for your milling machine, you should check out Online Carbide. They are an American manufacturer of high performance solid carbide cutting tools. When you visit www.onlinecarbide.com you will find manufacturer direct prices on products like jobber drills, stub drills, spot drills, drill mills, and several types of end mills. You can also reach out to a member of the Online Carbide team by sending an email to sales@onlinecarbide.com if you have any questions about their tools.
