Drilling holes with a milling machine seems like a straightforward process. Sadly, drill bits are long tools and their length can lead to natural oscillations during use. On particularly hard surfaces, a combination of spot drills and carbide drill bits will help produce the most accurate holes possible. It may require an additional tool change, but it is well worth the time if you want to drill a hole in a precise location.
Drill bits have a tendency to “walk” off their target when the surface being drilled is hard. This is because drill bits flex quite a bit under high speeds, though this can be hard to see with the naked eye. This issue is particularly prevalent when using steel tools due to metal’s inherent flexibility. Carbide drills do offer superior stability, but this does not mean that they are always able to be used without spot drilling.
The idea of using a spot drill is relatively simple. The spot drill bit has the shortest possible length which makes them incredibly stable. The cutting surface is minimal, so all it can do is “spot” the location of holes. This creates a small dimple that will guide the drill bit, significantly lowering the chance of having a drill bit miss its mark.
Many users confuse spot drills, carbide center drills, and stub drills. While a spot drill is designed to mark drilling locations, a center drill is designed to mark the mounting point for a lathe center. Center drills typically use a 60 degree point angle, which is significantly more narrow than spot drills, which use angles from 90 to 120 degrees. Stub drills are short drill bits that offer superior control when compared to standard length jobber bits. When choosing a cutting tool to begin a hole on your workpiece, the wide angle of a spot drill is going to be far more useful than attempting to mark the location with a center drill.
This larger angle is crucial because the spot drill angle should be large enough for the entire drill bit tip to seat in naturally. If you attempt to “spot drill” a drilling location with a narrow center drill, the twist drill bit might still deflect when you go to drill the final hole. A wide angle spot drill makes it easy to drill accurate holes once you start using your twist bits to drill holes.
To get the best results while spot drilling, be sure to run the spot drill for long enough to ensure that the spotted surface is as smooth as possible. Once the spot drilling is complete, using a stub length drill bit is going to be the best option in terms of accuracy because they are shorter and inherently more stable. Jobber length drill bits can also be used if the hole depth requires a depth that is deeper than a stub drill.
If you are looking for a wide variety of high quality carbide cutting tools, Online Carbide has all of the cutters your shop needs. You can spot drills and carbide drill bits that will help you machine precise parts. They offer end mills, drill bits, and other tools that are all machined from high quality carbide tool stock. These tools are available at manufacturer direct prices so you can always find a great deal on the tools you need. If you have any questions about their products you can reach a member of their team by calling 630-238-1424 or send an email to [email protected]