Drilling deserves more respect

Milling, turning and drilling are the foundational machining processes. Their chip removal processes are also the most efficient way to remove material from a workpiece. Of the three, drilling has the highest removal rate, which is why it’s the most efficient way to make chips. Evidence of this can be found when digging around an old shop.

By old, I mean one that is 40 or 50 years old and hasn’t been cleaned out. Not only will you find drills in ever imaginable diameter and length, they will have tapered shanks on them so that they can be used in every machine. The machine tools in the shop will also indicate that drilling is an efficient process. You can expect to find multiple spindle drill presses, radial arm drills and drill point grinders.

While drilling is a prominent and efficient process in modern shops, it is not utilized as frequently as it could be. Considering the advantages of drilling, shops today should be drilling far more often than they do.

Less Expensive

Drilling provides significant cost advantages over the other processes. With CNC controls and CAM software, a programmer can utilize milling techniques like helical entry, ramp entry and Z-axis plunging to make a hole. All of these techniques are effective methods, but drills typically cost less than milling tools and have a much longer service life. Also, given drilling’s higher material removal rate versus milling, it allows shops to reserve expensive milling machine time for more appropriate operations. Plus, drills move a larger volume of chips between sharpening, further reducing their lifetime cost.

Dependable Accurancy

When necessary, drilling can be very accurate. Valve housings for hydraulic power steering require close tolerance holes so that high pressure fittings seat and seal correctly. Specially designed drills are utilized and the holes are completed in one pass. The drilling process is capable of holding 0.005 mm hole diameters with a 0.4 µm surface finish. In many shops these holes would be created with multiple tools.

Drills Are Universal

Drilling on a lathe or a mill can be done with the same tools. Turning tools and milling tools, on the other hand, are usually not interchangeable across machine tools.

Easier To Program

Drilling processes are also much easier to create because the CNC controller has several canned drilling cycles available for use. Programming a drilling routine only requires a few lines of CNC code. Plus, drilling cycles are modal, meaning once a cycle is called, the programmer simply needs to provide the coordinates of the next hole, and then the cycle is repeated with a single line. Milling routines that make holes in parts require numerous lines of code and the number of lines only increases with complexity. What’s more, there are no canned cycles for milling.

Leveraging Special Drills

Complex internal geometries can be created using special drills. Multiple diameters, chamfers and radii can be made into the drill body so that other operations like boring are eliminated. This is especially helpful when the geometry has high length-to-diameter ratios. When the length-to-diameter ratio goes over 4:1, boring tools can become unstable and chatter becomes a problem.