Drilling a hole in a workpiece might sound like a pretty straightforward job, but the process can actually be quite complex depending on the material being used. Drill bits might be able to easily find purchase in a soft piece of wood, but dealing with metals is a whole other matter. In order to avoid having your drill bit walk off it’s mark, sometimes it will take multiple tools to drill the perfect hole. Using spot drills before drilling with a longer drill bit is the best way to produce accurate results every time.
When you think of a drill bit, the first image that usually comes to mind is your standard jobber length drill bit. These long twisted bits are perfect for drilling deep holes in your workpiece, but they come with their own unique issues. Because these cutting tools are so long relative to their diameter, drill bits have a tendency to be unstable. This can cause them to deflect off of hard surfaces and “walking” off their mark.
This issue is especially true at high speeds. The faster a tool rotates, the more it will naturally oscillate. Using rigid carbide drill bits can help to minimize the issue of tool oscillation, but it is hard to eliminate the issue entirely without using multiple tools. Spotting is one of the most efficient ways to drill extremely accurate holes in hard materials using your milling machine.
Spot drills are extremely short tools compared to a jobber drill bit. Instead of having the auger like flutes of a traditional drill bit, the cutting surface of a spot drill is limited to the tip. While these cutting tools are called drills, because they make axial cuts, they are not designed to drill holes. A spot drill’s short length makes them extremely stable, even at high rotational speeds. Instead of drilling a hole, spot drills are designed to mark the location of holes.
The point of a spot drill is to cut a small dimple in the surface of your workpiece wherever you plan on drilling a hole. This means that after spotting all of your hole locations, you can switch to your longer twist bit and drill extremely accurate holes. Because the longer drill bit will start drilling inside this dimple,there is almost no risk of the bit walking off its mark.
When it comes to knowing which spot drill to use, there are a few factors to consider. Obviously using solid carbide tools over steel will produce more accurate results. In addition to considering the material makeup of your cutter, you also need to look at the point angle. If the point on your spot drill is narrower than the point of your longer drill bit, then the second bit will contact the sides of the spot dimple instead of starting its cut at the base of the spot dimple. If the spotting point angle is larger than drilling point angle, then your drill bit should seat itself easily and drill a perfect hole no matter what material you are using.
If you want to find extremely accurate spot drills for your milling shop, you should check out the tools available at Online Carbide. They are an American tool manufacturer specializing in end mills and drill bits. All of their milling cutters are constructed from solid micro-grain tungsten carbide to ensure a long tool life. If you are interested in learning more about their tools or you are interested in having custom cutters machined for your shop, check out their online store at www.onlinecarbide.com.