MARCH 2005 / VOLUME 57 / NUMBER 3 special focus: holemaking ➤ BY BILL KENNEDY, CONTRIBUTING EDITOR STEADYSTEADY as it guides

While rigid, accurate CNC machine and modern drill designs minimize the need for drill bushings, the well-proven concept remains a valuable for select applications.

or decades, drill bush- Drill bushings ings were required for Side view F precision holemaking operations. A shop would Locking build a fixture to lock in the Workpiece relative positions of the Top view Location pins drill and part, then use a jig Jigjig fitted with a hardened-steel bushing to guide the drill. Such setups ensured that Workpiece the drill entered the work- piece straight and produced Drill bushings an accurate hole. It also

eliminated the need for B. Kennedy pilot holes; prevented drill In a classic drill bushing setup, a jig is located and wandering and chatter locked onto the workpiece to assure repeatable when holes in an- positioning of the drill bushings and resultant holes. gled surfaces; provided sta- bility when drill overhang was exces- ago, automotive plants employed sive; and reduced tool breakage. transfer lines with dedicated machines Today, drill bushing use is in decline. arranged in multiple stations. “They The main reasons are the emergence of would use drill bushings at every sta- rigid, fast CNC machine tools and ad- tion where they used a drill,” he said. vanced drill designs. CNC machines Today, most automotive work is done can apply a spot drill and quickly fol- on CNC machines, where “there usu- low it with the drill that penetrates to ally isn’t space in the fixture to mount the specified depth. And sophisticated a bushing,” Stewart said.

Acme geometries allow drills to enter a work- “Drill bushings were big for 50 or 60 A drill bushing positions and stabilizes piece without spotting. years,” said Al Rocheford, who manages the drill to assure precision and Scott Stewart, applications engineer daily operations at Axly Tool & Bush- repeatability. at International Drill Guide Inc., An- ing, a Briney Tooling Systems company derson, S.C., pointed out that 30 years located in Bad Axe, Mich. Axly still manufactures bushings and supports ex- isting installations, but the standard drill Bushing basics bushings that formerly made up the bulk of Axly’s output now constitute only he most widely used and least expensive drill bushing style is the press-fit about 8 percent of its business. T (ANSI Type P). These simple, short, hollow cylinders of hardened steel are Ray Yillik, founder of carbide bush- pressed into the drill jig. ing maker Yillik Precision Industries, A step beyond the Type P is the Type H, or head press-fit, which has a head Ontario, Calif., said: “In the smaller or shoulder on the bushing’s drill entry end. The head is designed to resist axial tool-and-die and production shops, they forces that can force a headless bushing out of the jig plate. The Type H’s head are still using drill bushings. The tech- limits how close together the bushings can be placed in the jig, and mounting nology is good. It works. But the reality holes must be counterbored if a flush fit with the jig plate is desired. For prac- is that it is a dying commodity, because tical purposes, Type P and H bushings are permanently installed in the jig and the machines are getting so good.” are best for production runs where wear-related replacement isn’t necessary, and where only one diameter of drill or is applied.

Types P and L—Headless press-fit or headless liner

Type H—Headed press-fit illik Precision Y Drill bushings made of tungsten carbide Type HL—Headed liner can provide 10 to 50 times the wear life of plain steel bushings.

Filling Needs While widespread use of commod- Type SF—Slip/fixed renewable ity-type drill bushings is on the decline, demand persists for bushings that fill specific needs. Marshall Johnston, plant manager for All American Prod- Type FM—Fixed renewable

ucts Co., San Fernando, Calif., offered All American the example of a pin-locking bushing Type SF (slip/fixed renewable) and Type FM (fixed renewable) bushings fit into system that sees frequent application in headless liner (L) or headed liner bushings (HL) that are pressed into mounting the aerospace industry. The bushings holes in the jig. The bushings are held in the liners by lock or clamps, which are for use with a small (3⁄32" to 1⁄2"in permit the bushing to be changed quickly. Type SF and FM bushings work well on diameter) drill and an air-fed drill long production runs in which bushings need to be replaced as they wear, as well motor. Johnston said the system is as in situations where multiple tool diameters (e.g., drilling and reaming) are used. “real handy to get in small places.” Some bushings feature OD serrations or knurled patterns designed to grip jigs The drill motor is fairly small and made of softer materials. Type DG (diamond groove) bushings feature a knurled compact, akin to a hand drill. The pattern on the OD to enhance their grip in the jig. SG (serrata groove) bushings bushing system consists of a liner that have straight serrations that aid pressing into a jig made of a softer material. is mounted in the jig plate and a bush- Type SP (serrata press) bushings have serrations and also a finish-ground OD to ing that is secured in the liner with a facilitate press-in installation in soft materials. pin lock. “A little twist lock, with a 30û Bushing manufacturers also add functional features to their products such as turn, locks it in place. It makes it a lot chip control geometry on the edge facing the workpiece. Other bushings are de- easier for the operator, and it speeds up signed with ports to feed oil or coolant through the bushing body to clear chips the operation, too,” Johnston said. and cool the cutting zone. Johnston added that demand for ser- —B. Kennedy rated press bushings engineered for use in softer jig plate materials, such as alu- tomotive industry. Such products often The following companies minum (see sidebar, page 65), appears employ difficult-to-machine or abra- contributed to this report: to be increasing as “more people are sive materials, and tungsten carbide using aluminum for jig plates instead bushings provide advantages over steel Acme Industrial Co. of steel because they are a lot lighter to ones when side loads on the drill or (800) 323-5582 move around. Keeps people from hurt- abrasion from chips generate excessive www.acmeindustrial.com ing their backs.” bushing wear. Yillik said one application area for Yillik said a carbide bushing typi- All American Products Co. his company’s carbide bushings is pro- cally costs five times more than a com- (818) 361-0059 prietary product development in the au- parable steel bushing, but provides www.allamericanproducts.com from 10 to 50 times the wear life. In Axly Tool & Bushing Inc. When you get lemons ... long production runs, he said, it is easy to justify the extra cost. “If they are (800) 248-0622 www.brineytooling.com … make lemonade. Successful com- drilling 100,000 holes, they are better panies recognize and adapt to chal- off using the steel bushing, but if they International Drill Guide Inc. lenges that can come in strange forms. are drilling a million or 2 million holes, (864) 225-2214 For example, a manufacturer’s respected then they should look at carbide … www.gundrill.com trademark may become associated with they are crazy if they don’t.” a completely different image. Yillik Precision Industries Witness E.I. du Pont de Nemours & Long and Deep (800) 854-9847 Co.’s registered Teflon trademark. The Another continuing application for www.yillik.com well-known product name gained unin- drill bushings, Yillik said, is gun- tended subconscious baggage when the media named organized crime fig- counterpoint ure John Gotti “The Teflon Don” after prosecutors couldn’t make their o support and guide the drill, the bushing ID or bearing surface at its work- charges stick. T piece end must be just slightly larger than the drill diameter, within a spec- Acme Industrial Co., Carpentersville, ified range. For example, for 1⁄4"- to 3⁄4"-dia. drills, a typical ID bearing surface Ill., has been serving customers for over tolerance is between 0.0005" and 0.0006" larger than the drill diameter. In other 90 years. For the last 55 of those years, words, for a 1⁄2"-dia. drill, the bearing surface ID tolerance is from 0.5005" to a certain animated desert bird has used 0.5006". But the bearing surface does not have to extend the entire length of the “Acme” products to counter the attacks bushing. For example, for a 1"-long, 1⁄4"-dia. 5 of one hapless cartoon coyote. drill bushing, the bearing surface might be ⁄8" Counterbore On its Web site, Acme steps up and long. The rest of the bushing can be counter- acknowledges the situation. The com- bored or relieved to a larger diameter, but pany immediately points out the con- this a somewhat controversial matter. No counterbore Full bearing trast between its products, quality and Acme Industrial Co. manufactures its stan- surface supports service and the often bizarre actions of dard bushings without , offer- the tool for the that odd couple of the Southwest: ing counterbored bushings as specials. Other entire length of “Acme Industrial Co. has a proven bushing makers reverse that policy, making bushing.

track record of providing the highest no-counterbore bushings a special-order Acme quality products and service to manu- item. Acme President John Evans said the Opinion varies as to whether a facturers around the world since 1914. company believes the no-counterbore de- counterbored drill bushing (left) No shoddy rocket-powered roller sign produces a more accurate and more ver- provides an escape path for chips skates, giant slingshots or coyote- satile bushing. “We also think it helps the and coolant or promotes chip crushing anvils here. We manufacture tool to last longer,” he said. “When you go packing and increased tool wear. precision no-counterbore drill bushings from the counterbore to the bearing sur- and keylocking threaded inserts to the face, there’s usually a sharp corner. If the tool isn’t lined up exactly, it could hit highest levels of workmanship.” the corner in there and chip the drill or the bushing.” Acme’s strong statement clears away Evans said Acme believes that with counterbored bushings “often times, the any subconscious connections with the chips will pack up in there and seize up the tool.” He said makers of counterbored cartoon company, and by contrast re- bushings argue the other way, that the counterbore allows chips and coolant to inforces the company’s real-world his- escape the cutting zone. “Some of them actually call it a chip clearance,” he said, tory of quality and service. Pretty wily, “but there again, depending on the material you’re drilling and the type of tool wouldn’t you say? you’re using, it will pack up in there.” —B. Kennedy —B. Kennedy drilling. The reason is that a gundrill is not a self-piloting tool. The off-center configuration of the gundrill’s flute dictates the use of a starter hole or guidance provided by a bushing. Usu- ally on CNC mills and lathes there is no practical way to set up a jig plate and bushing. In that case, a deep hole can be located with a spot drill run to a depth of 1⁄2 or 3⁄4 of the drill diameter, then be completed with a gundrill. The high-pressure coolant capability avail- International Drill Guide able on many CNC machines clears the Because a gundrill is not self-positioning, a drill bushing (right) is used chips from deep holes. on the workpiece side of the gundrill’s chip box to direct the tool into However, for high-volume produc- the workpiece. At left, a polymer guide bushing damps vibration, tion of deep holes, “there are still a lot stabilizes the drill and seals chips and coolants in the chip box.

Bushing business of people purchasing dedicated gun- ring at all,” the guides dampen the en- drilling machines,” said International ergy that can make a long, thin drill vi- ith 200,000 bushing sizes in Drill Guide’s Stewart. “The fastest, brate and chatter. Consequently, shops W stock, All American Products most efficient way to gundrill is to pilot also use polymer guides in a machine’s Co. probably has “the largest inven- the tool through a bushing rather than a steady rest to stabilize long gundrills. tory in the world,” said plant manager prequalified hole.” Stewart said his company’s primary Marshall Johnston. “When we make The drill bushing on a dedicated gun- customers are automotive companies stock for our inventory, we make about drilling machine is 2 to 3 years’ supply at a time.” located at the front A carbide bushing typically costs five times Why? “When a guy needs a bushing, of a chip box into more than a comparable steel bushing, but he wants it now. It’s the last thing he which chips and remembers when he is assembling his coolant flow as they provides from 10 to 50 times the wear life. fixture. He doesn’t want to wait 3 or 4 are forced along the weeks for it to come by boat, or spend drill flutes and out of the hole. and their Tier 1 suppliers who use ded- money to fly it across the Big Pond,” International Drill Guide provides icated gundrilling machines to drill Johnston said. polymer drill guides that ride in a bear- cylinder heads, engine blocks, In this age of finance-department- ing at the back of the chip box and seal camshafts, crankshafts and other pow- dictated skeletal inventories and just- in the chips and coolant. The center ertrain components. in-time supply, the policy is a throw- hole of the guide mirrors the distinc- No matter the application, the need for back. “Yes, it’s old-fashioned,” John- tive cross-section of a gundrill. The drill bushings is definitely on the wane. ston said. “But it’s easier to sell if you polymer construction enables the The technology, said Yillik, “is not have a full cart.” Minimal inventory, guide to stretch over the gundrill tip something that 10 or 15 years from now he said, “is not good for the trade. It and conform to the drill shaft, creating there is going to be much call for.” How- really isn’t good for the customer.” As a tight seal. ever, applications will persist where cer- a result, Johnston said, All American Stewart said polymer guides have tain drill bushing styles and materials faces minimal overseas competition. other benefits. Because “metal parts provide precision and productivity in —B. Kennedy ring like a bell, and polymer parts don’t specific holemaking operations.

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