A short story about the parabolic flute drill

March 11, 2020 - 04:15pm
A short story about the parabolic flute drill

I received an email from Lynn Fifer, a retired cutting tool professional and CTE reader since 1967, who shared his recollections about the development of the parabolic flute drill. Fifer said the development occurred in 1950s at the old Mohawk Tools Inc., Montpelier, Ohio, well before he started with the toolmaker in 1967.

Fifer stated Frank Hofbauer, company founder and CEO, took a trip to his home country, Germany, to see some customers, as well as visit family and relatives. Volkswagen was one such customer, which was facing challenges with deep-hole drilling aluminum engine blocks. Hofbauer returned home with part prints and application information for his son Bill to work on. Mohawk also received aluminum engine blocks for test drilling.

“Like any tool engineer, Bill looked at the cross section of a drill and tried to come up with a design that would allow a lot of chips to flow up the flutes without any restrictions but still retain adequate longitudinal column strength,” Fifer noted. “He increased the web to about 38% of diameter for strength, which decreased the flute capacity. So to increase capacity, he rolled off the heal of the land to open up the flutes. With a heavy web at the point, and so as not to restrict chip flow, it would need to be a straight or parallel web.”

Usually, a drill with a thick web requires web thinning or a split point, Fifer continued. “A flatter point angle would direct the chips into the flute better, but the conventional split or crankshaft drill point didn’t work well in aluminum, so the split was modified with a radius and the web across the center was increased slightly for the aluminum.”

After successfully testing the drill, Fifer stated that Bill Hofbauer was not satisfied with having to take two passes during the flute grinding operation and brought in a man named Bill Hertlein to design a horizontal dresser to generate the parabolic flute in one pass.

Eventually, the head of Guhring at the time saw the unique drill at the VW factory, Fifer added. “A patent was never sought, and the GT 100 was born,” he noted about Guhring’s parabolic drill. “The rest is history.”

Related Glossary Terms

  • flutes


    Grooves and spaces in the body of a tool that permit chip removal from, and cutting-fluid application to, the point of cut.

  • grinding


    Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.

  • land


    Part of the tool body that remains after the flutes are cut.

  • parallel


    Strip or block of precision-ground stock used to elevate a workpiece, while keeping it parallel to the worktable, to prevent cutter/table contact.

  • point angle

    point angle

    Included angle at the point of a twist drill or similar tool; for general-purpose tools, the point angle is typically 118°.

  • sawing machine ( saw)

    sawing machine ( saw)

    Machine designed to use a serrated-tooth blade to cut metal or other material. Comes in a wide variety of styles but takes one of four basic forms: hacksaw (a simple, rugged machine that uses a reciprocating motion to part metal or other material); cold or circular saw (powers a circular blade that cuts structural materials); bandsaw (runs an endless band; the two basic types are cutoff and contour band machines, which cut intricate contours and shapes); and abrasive cutoff saw (similar in appearance to the cold saw, but uses an abrasive disc that rotates at high speeds rather than a blade with serrated teeth).

  • web


    On a rotating tool, the portion of the tool body that joins the lands. Web is thicker at the shank end, relative to the point end, providing maximum torsional strength.



Alan holds a bachelor’s degree in journalism from Southern Illinois University Carbondale. Including his 20 years at CTE, Alan has more than 30 years of trade journalism experience.


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