Drill Basics

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Revision as of 21:34, 8 September 2011 by Eburdick (talk | contribs)

For most robotics work, we are drilling in metal, mostly aluminum. We also drill plastics and wood on occasion. Different materials act differently when being drilled, so it is important to know what kind of drill is best for each material, and how fast to spin and feed the drill. There are lots of fancy and expensive drills out there for various materials, but we will concentrate here on things we are likely to find in our shops.

Tip designs

Most twist drills we are likely to see in our shops have either a 118 degree or 135 degree tip. The 118 degree tip has a longer cutting edge, and follows a pilot hole more easily. The 135 degree tip has a shorter cutting edge and gets past the tip earlier in the drilling process, but does not follow a pilot hole as easily. A common variation is the "split point" design, which is often found paired with a 135 degree tip angle. This drill type has a "multifaceted" tip with a more aggressive cutting angle and a greatly shortened flank behind the cutting edge. The extra facet that shortens the flank also cuts into the chisel edge, forming a point that walks much less when drilling without a punched or drilled pilot.

Split point drill tip.jpg

Because these drills take a deeper bite, they are generally not recommended for aluminum, and though the tip is better at self centering, it does not follow a pilot as well as a conventional drill.

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Aluminum is considered a "stringy" metal because it forms long chips when it is cut. In fact, some cutting tools will form a single chip several feet long when drilling a hole in aluminum. A big challenge is providing an escape route for the aluminum chip. In twist drills, the recommended type is one with a "fast spiral" design. The three pictures below show examples of fast spiral, normal, and slow spiral designs. Though the fast spiral design is better at clearing aluminum chips, this is not generally critical for manual drilling.

Fast spiral drill.jpg Normal spiral drill.jpg Slow spiral drill.jpg