Light machining

Author Cutting Tool Engineering
June 01, 2011 - 11:15am

Craig Brosius, president and CEO of American Concepts and Technologies Inc., said his job shop focuses on “innovation and diversity.” ACT, Anoka, Minn., serves customers in numerous industries, including companies such as TorchLAB, a maker of compact flashlights. 

Tom Goetzen, TorchLAB owner and engineer, said his modular, high-performance flashlights, trade named Moddoolar, are virtually “future proof” because they have interchangeable bodies, switches and heads. “As technology changes and as people want newer technology and even more power in a flashlight, we can fit anything they want to our standard platform,” he said. 

The lights incorporate three advanced LEDs with a total output of 800 to 1,100 lumens, roughly equivalent to that of a typical low-beam, halogen automobile headlight. The flashlights have a maximum diameter of 1.25" and overall lengths from 3.75" to 7.75". 

Goetzen approached Brosius to machine the tubes that hold the lithium energy cells. Brosius produces five different versions of the cell tubes, all identical except lengths range from 2" to almost 6". 

The machining process begins with 1⅛"-dia. 6061-T6 aluminum bar stock, cut into 3 '-long sections and fed through the 2"-dia. through-hole spindle of a 2010 Mazak QTN-150 CNC lathe. Brosius first faces and OD turns the bar with a Kennametal CNMP431 coated carbide insert. He noted that nearly all of the shop’s metalcutting tools are from Kennametal, and all the cutting tools referenced in this article are from Kennametal. 

Then, instead of applying a conventional knurling tool to form the knurl pattern into the workpiece surface, Brosius employs an efficient, controllable and repeatable method to knurl the central section of the cell tube. That’s because Goetzen was dissatisfied with the consistency of common knurling techniques. 

“It is very difficult to specify an exact knurl pattern, depth and feel,” Goetzen said. “Sometimes it is too sharp, sometimes it’s too smooth, and the depth of the impressions and the width of the diamond shapes can be difficult to control. It can vary from one run of parts to the next, even from the same shop. Beyond looking nice, the body of the flashlight is what you hold in your hand, and how it feels and the grip it provides is really important.”

Goetzen said he experimented with different patterns and depths on ProEngineer Wildfire CAD, and “eventually came up with something that looks great and performs well also.” Five-axis milling with a ball endmill can produce a knurled surface, but that typically creates unwanted deep valleys and sharp corners, he noted. “I wanted something that was a little more aggressive without the typical abrasiveness of a deep knurl,” Goetzen said.

Goetzen and Brosius decided to turn the knurl on the Mazak lathe. “To get the diamonds to the right size and figure out what kind of tooling to use, I started playing around with the threading options offered by the Mazatrol conversational CNC,” Brosius said. 

The chosen pattern was a 12-entrance thread with a 1½" pitch. Instead of cutting a single path around the bar, as in a simple screw thread, the toolpaths start at 12 points around the bar circumference. Each toolpath creates a spiral entirely around the part. Twelve threads are cut with a Top Notch 0.125"-wide, full-radius, right-hand grooving insert. Then the lathe spindle is reversed, and a Top Notch left-hand tool cuts 12 threads the other way. The reverse set of spirals on top of the first set produces the diamond-shaped knurl pattern. Each spiral is cut in a single 0.010"-deep pass. 

Typical threading speed for an aluminum bar of this diameter would be 300 to 400 sfm, but with the 1½" pitch of the spiral, the tool is “moving pretty quickly” at those speeds, Brosius explained. So, to minimize stress on the machine tool, he slows the cutting speed. “I got the best finish at 100 sfm,” he said, “and it mimicked about 50 percent of the speed of my rapids, kind of an even flow back and forth over the part.” 

The Mazatrol software automatically calculates feed rate in relation to pitch and cutting speed. Knurling the longest tube consumes about 44 seconds. “It works beautifully,” Brosius said. “No cleanup pass is necessary.”

The low-force nature of the knurling process enables Brosius to produce the knurl on the three shorter tubes without the use of a tailstock. For the two longer versions, after facing and OD turning the part, he center-drills the bar face and brings in a programmable tailstock for support during knurling.

Brosius noted that the knurl starts and ends in the middle portion of the cell tube. “By doing some calculations and changing the starting points and end points for the thread, I am able to keep that accurate within a couple thousandths.” 


Courtesy of ACT

American Concepts and Technologies machined all details of this aluminum cell tube for a TorchLAB high-performance flashlight, including its unique "Diamondback" knurl pattern.

After cutting the knurl, Brosius machines three O-ring grooves around the OD, one at one end of the tube and two at the other. Rubber O-rings later seated in the groove guarantee sealing against the elements.

Brosius cuts the O-ring grooves with a Top Notch 0.031"-wide coated insert run at 800 sfm and 0.007 ipr. He then machines a 1-20 thread at one end of the tube and a ⅞-20 thread at the other end, for the flashlight end cap/switch and head, respectively.

The tube ID is drilled with a Kentip 0.720"-dia. modular drill, run at 1,000 sfm and 0.015 ipr. The drill does not penetrate the entire finished length of the tube and leaves about 0.008" excess per side for finish boring to a diameter of 0.736". The no-peck drilling cycle takes about 9 seconds for the longest tube. 

A ⅝"-dia. boring bar tooled with a CCGT2151 indexable insert finishes the bore and leaves a 0.04"-wide shoulder at its bottom. A 0.650"-dia., solid-carbide, through-coolant drill then completes the bore through the full length of the tube. 

Tolerances for the O-ring grooves are ±0.001". According to Goetzen, Brosius “really has the process dialed in. The parts are looking fantastic.” Goetzen has trade named the tube pattern “Diamondback” knurling. 

Brosius machines the tubes in lots of 500 to 600 pieces, after which the tubes are tumbled and hard-coated by TorchLAB. CTE

For more information about American Concepts and Technologies Inc., call (763) 421-1036. For more information about TorchLAB flashlights, visit or

Related Glossary Terms

  • boring


    Enlarging a hole that already has been drilled or cored. Generally, it is an operation of truing the previously drilled hole with a single-point, lathe-type tool. Boring is essentially internal turning, in that usually a single-point cutting tool forms the internal shape. Some tools are available with two cutting edges to balance cutting forces.

  • boring bar

    boring bar

    Essentially a cantilever beam that holds one or more cutting tools in position during a boring operation. Can be held stationary and moved axially while the workpiece revolves around it, or revolved and moved axially while the workpiece is held stationary, or a combination of these actions. Installed on milling, drilling and boring machines, as well as lathes and machining centers.

  • computer numerical control ( CNC)

    computer numerical control ( CNC)

    Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.

  • computer-aided design ( CAD)

    computer-aided design ( CAD)

    Product-design functions performed with the help of computers and special software.

  • cutting speed

    cutting speed

    Tangential velocity on the surface of the tool or workpiece at the cutting interface. The formula for cutting speed (sfm) is tool diameter 5 0.26 5 spindle speed (rpm). The formula for feed per tooth (fpt) is table feed (ipm)/number of flutes/spindle speed (rpm). The formula for spindle speed (rpm) is cutting speed (sfm) 5 3.82/tool diameter. The formula for table feed (ipm) is feed per tooth (ftp) 5 number of tool flutes 5 spindle speed (rpm).

  • endmill


    Milling cutter held by its shank that cuts on its periphery and, if so configured, on its free end. Takes a variety of shapes (single- and double-end, roughing, ballnose and cup-end) and sizes (stub, medium, long and extra-long). Also comes with differing numbers of flutes.

  • feed


    Rate of change of position of the tool as a whole, relative to the workpiece while cutting.

  • gang cutting ( milling)

    gang cutting ( milling)

    Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.

  • grooving


    Machining grooves and shallow channels. Example: grooving ball-bearing raceways. Typically performed by tools that are capable of light cuts at high feed rates. Imparts high-quality finish.

  • indexable insert

    indexable insert

    Replaceable tool that clamps into a tool body, drill, mill or other cutter body designed to accommodate inserts. Most inserts are made of cemented carbide. Often they are coated with a hard material. Other insert materials are ceramic, cermet, polycrystalline cubic boron nitride and polycrystalline diamond. The insert is used until dull, then indexed, or turned, to expose a fresh cutting edge. When the entire insert is dull, it is usually discarded. Some inserts can be resharpened.

  • inner diameter ( ID)

    inner diameter ( ID)

    Dimension that defines the inside diameter of a cavity or hole. See OD, outer diameter.

  • knurling


    Chipless material-displacement process that is usually accomplished on a lathe by forcing a knurling die into the surface of a rotating workpiece to create a pattern. Knurling is often performed to create a decorative or gripping surface and repair undersized shafts.

  • knurling tool

    knurling tool

    Normally a lathe tool for impressing a design on a rod or handle to improve gripping or provide decoration.

  • lathe


    Turning machine capable of sawing, milling, grinding, gear-cutting, drilling, reaming, boring, threading, facing, chamfering, grooving, knurling, spinning, parting, necking, taper-cutting, and cam- and eccentric-cutting, as well as step- and straight-turning. Comes in a variety of forms, ranging from manual to semiautomatic to fully automatic, with major types being engine lathes, turning and contouring lathes, turret lathes and numerical-control lathes. The engine lathe consists of a headstock and spindle, tailstock, bed, carriage (complete with apron) and cross slides. Features include gear- (speed) and feed-selector levers, toolpost, compound rest, lead screw and reversing lead screw, threading dial and rapid-traverse lever. Special lathe types include through-the-spindle, camshaft and crankshaft, brake drum and rotor, spinning and gun-barrel machines. Toolroom and bench lathes are used for precision work; the former for tool-and-die work and similar tasks, the latter for small workpieces (instruments, watches), normally without a power feed. Models are typically designated according to their “swing,” or the largest-diameter workpiece that can be rotated; bed length, or the distance between centers; and horsepower generated. See turning machine.

  • metalcutting ( material cutting)

    metalcutting ( material cutting)

    Any machining process used to part metal or other material or give a workpiece a new configuration. Conventionally applies to machining operations in which a cutting tool mechanically removes material in the form of chips; applies to any process in which metal or material is removed to create new shapes. See metalforming.

  • milling


    Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.

  • outer diameter ( OD)

    outer diameter ( OD)

    Dimension that defines the exterior diameter of a cylindrical or round part. See ID, inner diameter.

  • pitch


    1. On a saw blade, the number of teeth per inch. 2. In threading, the number of threads per inch.

  • threading


    Process of both external (e.g., thread milling) and internal (e.g., tapping, thread milling) cutting, turning and rolling of threads into particular material. Standardized specifications are available to determine the desired results of the threading process. Numerous thread-series designations are written for specific applications. Threading often is performed on a lathe. Specifications such as thread height are critical in determining the strength of the threads. The material used is taken into consideration in determining the expected results of any particular application for that threaded piece. In external threading, a calculated depth is required as well as a particular angle to the cut. To perform internal threading, the exact diameter to bore the hole is critical before threading. The threads are distinguished from one another by the amount of tolerance and/or allowance that is specified. See turning.

  • through-hole


    Hole or cavity cut in a solid shape that connects with other holes or extends all the way through the workpiece.

  • toolpath( cutter path)

    toolpath( cutter path)

    2-D or 3-D path generated by program code or a CAM system and followed by tool when machining a part.

  • turning


    Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.