VIDEO: Tech Tip #8 – Fundamentals of Drilling

In turning and milling, chip formation and chip evacuation is not usually a tremendous issue, unless you're milling full slots. In drilling applications, the challenge is far greater. Take a look at the tip of this drill. This is the part that does all the cutting of the material. It forms the chips by spinning as it's pushed straight into the material. The center of the drill never changes position, so the speed at the center of the drill is essentially zero. As you look further out along the cutting edges from the center of the drill, the speed changes. This makes proper chip formation quite complicated.

Now consider chip evacuation. Where did the chips have to go? Think about it. When making a hole the drill goes straight into the material. The hole is essentially the same size as the tool itself, so the chips have nowhere to go when they're cut. That's why chip evacuation is so critical. You can't have chips stay in the hole, otherwise, they will get in the way of the drill point reaching new material and re-cutting chips. This is often how drills break and how hole quality is decreased. In order for the chips to be evacuated properly, they have to break and travel up the flutes of the drill toward the spindle to be released.

In turning and milling, external coolant is very often sufficient for providing temperature control. However, in drilling external coolant cannot reach the point of the drill, particularly in longer applications with a length-to-diameter ratio greater than 3xD. Because of this, internal coolant is required for proper heat management in hole making applications. Internal coolant is not only important for heat management, but also for chip evacuation. Like we talked about before, internal coolant helps to apply force to the chips and flush them out up through the flutes. These are all factors to consider when deciding which drill to purchase for your applications. You always want to make sure that it's fully equipped and engineered specifically for the type of material that you're cutting, is prepared for proper chip evacuation with polished chip flutes for easy evacuation, and that it provides efficient internal coolant supply for drills greater than 3xD in length for proper heat management and chip evacuation.

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