Difference between revisions of "How to Drill Holes where You Want Them"

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==Introduction==
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Usually when you drill holes as part of robot construction, it usually matters where they are, and this is often a significant challenge, even when you are using a drill press. The key issue that makes it difficult is "walking" of the drill as the initial cut starts.  This is just because the drill is turning, and the tip is not a single point.  Even on the drill press, smaller drills flex, and a hole can start off center.  To start, let us look at the tip of a twist drill.
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[[File:Twist_drill_nomenclature.jpg]]
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==The Walking Drill==
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Note that the tip of the drill is not a single point, but a straight chisel edge that runs across the end of the drill's web.  If you put this chisel edge against a piece of metal (the work) and turn it, then it will want to walk along the surface, pivoting on the chisel edge corners.  If the drill is held rigidly in place, the chisel edge will scrape away a circle of material as the beginning of the drilling process, and as it goes deeper, the cutting edges start cutting a cone-shaped depression that matches the shape of the drill point. This depression keeps the drill on center for the rest of the drilling operation, but even then, if the tip of the drill is not perfectly symmetric, or if the drill is not perpendicular to the surface, or if the material has uneven hardness, the drill can cut more on one side than another and drift until the entire point is below the surface.
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==Center Punching==
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The most common approach to keeping a drill from walking is to use a center punch to create an initial starting cone.  If this cone is significantly bigger than the chisel point of the drill, then we have centering forces from the beginning, but as soon as the center punched part is cut away, the drill can still drift because of uneven cutting.  The best situation is if the punched cone is bigger than the entire diameter of the drill, which is clearly not going to happen with even moderately large drills.
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==Center drilling==
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==Holding the drill tip in place==
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===Center Punching===
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The most common method of establishing a starting point for drilling is the use of a center punch.  This creates a cone shaped depression in the material to guide the drill.  If the cone is bigger than the drill tip, then it can guide the drill into the right position.  If the drill tip is bigger than the cone, then center-punching can do more harm than good, so it is important to use a small pilot drill for
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Revision as of 23:50, 7 September 2011

Back to Mechanical Tutorials Home

Introduction

Usually when you drill holes as part of robot construction, it usually matters where they are, and this is often a significant challenge, even when you are using a drill press. The key issue that makes it difficult is "walking" of the drill as the initial cut starts. This is just because the drill is turning, and the tip is not a single point. Even on the drill press, smaller drills flex, and a hole can start off center. To start, let us look at the tip of a twist drill.

Twist drill nomenclature.jpg

The Walking Drill

Note that the tip of the drill is not a single point, but a straight chisel edge that runs across the end of the drill's web. If you put this chisel edge against a piece of metal (the work) and turn it, then it will want to walk along the surface, pivoting on the chisel edge corners. If the drill is held rigidly in place, the chisel edge will scrape away a circle of material as the beginning of the drilling process, and as it goes deeper, the cutting edges start cutting a cone-shaped depression that matches the shape of the drill point. This depression keeps the drill on center for the rest of the drilling operation, but even then, if the tip of the drill is not perfectly symmetric, or if the drill is not perpendicular to the surface, or if the material has uneven hardness, the drill can cut more on one side than another and drift until the entire point is below the surface.

Center Punching

The most common approach to keeping a drill from walking is to use a center punch to create an initial starting cone. If this cone is significantly bigger than the chisel point of the drill, then we have centering forces from the beginning, but as soon as the center punched part is cut away, the drill can still drift because of uneven cutting. The best situation is if the punched cone is bigger than the entire diameter of the drill, which is clearly not going to happen with even moderately large drills.

Center drilling

Holding the drill tip in place

Center Punching

The most common method of establishing a starting point for drilling is the use of a center punch. This creates a cone shaped depression in the material to guide the drill. If the cone is bigger than the drill tip, then it can guide the drill into the right position. If the drill tip is bigger than the cone, then center-punching can do more harm than good, so it is important to use a small pilot drill for

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