John Prosock Machine Inc. is a Quakertown, Pa., job shop that handles prototype machining as well as production and assembly jobs. Founded in 1982, the 30-employee shop has 10 mills and 13 lathes. Production runs range from 100 to 2,000 pieces for a range of customers. “We pretty much do anything,” said Claude Farrington, plant manager. “Medical work, driveline components, heavy equipment, parts for remote-control cars, you name it.”
Describing the machining of a prototype aluminum trunnion housing, Farrington said the actual machining of the complex-looking part was not too difficult, but determining how to fixture it was a challenge. The roughly 11½ "-long × 5½ "-wide housing was designed to mount on a boat’s transom and house an electronic linear actuator. It is part of a system that provides instant steering response when activated by controls at the helm, eliminating the slow reactions of a cable system.
Prosock Machine received a DXF file from its customer and loaded it into the shop’s Mastercam CAM software to program milling operations. Turning work was programmed at the lathe.
The housing was machined from a 12 "×6 "×3½ " 6061-T6 aluminum block. It was clamped with the long dimension standing vertical in a Kurt vise with aluminum soft jaws on an Excel 810 vertical machining center. One end of the finished housing has a single 1.850 "-dia., 3.850 "-long boss, but, to start, two identical bosses were machined side-by-side. “We machined two so when we flipped the part we could use them to align it in the vise. Later we cut the one off that we didn’t need,” Farrington said.
The twin bosses were machined with a 1½ "-dia. HSS endmill, run at 3,000 rpm and a 30-ipm feed rate with a 4 " length of cut. Farrington described the toolpath as “a figure 8 around the bosses,” stepping down 0.200 " on each pass.
Courtesy of John Prosock Machine
John Prosock Machine produced this aluminum trunnion housing as a prototype for part of a powerboat steering system.
The housing was then flipped in the vise and one of the twin bosses was located against a stop. On the other end of the finished housing would be two bosses that are not identical, having different diameters and offset 70° from each other. One boss, in line with a boss machined earlier, measures 2.100 " in diameter. The other boss is 1.514 " in diameter. Because this second set of bosses was closer together than the first pair, smaller endmills were used. The bosses were roughed with a ⅞ "-dia. HSS hogmill and finished with a ¾ "-dia. HSS endmill, both run at 1,200 rpm and 10 ipm with a 4 " length of cut. The two bosses are 1.360 " long, but one is set back 0.600 " deeper in the part than the other.
Water-soluble coolant was applied throughout the machining process. Farrington described the HSS tools as “generic,” adding that the shop’s solid-carbide tools are from Mill Monster and its inserted milling and turning tools are from Kennametal.
After milling the second set of bosses, the smaller diameter one was drilled and reamed. A 11⁄16 "-dia. HSS drill, run at 600 rpm and a 4-ipm feed and pecking each 0.200 ", drilled to a depth of 7.7 ". A 1.103 "-dia. reamer then finished the hole to a tolerance of ±0.0004 ". At this point, the housing was removed from the VMC and the extra boss machined in the first operation was removed with a bandsaw, leaving a stub to be face-turned away later.
Next, the part was clamped horizontally in the vise and a 3 "-dia. shell mill, run at 2,500 rpm and 20 ipm, facemilled the housing to height of the next feature, a 3.5 "-wide × 2.7 "-long × 0.72 "-deep pocket, which would hold the actuator electronics. A ½ "-dia. carbide endmill run at 3,500 rpm and 25 ipm roughed out the pocket, leaving 0.050 " of extra stock on the sides and 0.010 " on the floor. Then, a ¼ "-dia. carbide endmill finished the side profiles and bottom. A small pocket in the bottom of the larger feature required machining with a 1⁄32 "-dia. carbide endmill. Outside each corner of the pocket, a hole was drilled 0.433 " deep with a 0.114 "-dia. drill and threaded with an M3.5×0.6 tap.
The next operation was milling the back of the housing. The part was flipped in the vise, the 3 "-dia. shell mill removed excess material, and a ½ "-dia. carbide endmill roughed and finished the details. The sharp edges of a lug created in the operation then were rounded with a radius mill.
Next, the housing was moved to a Eurotech turning center for turning, facing and boring. With the 2.100 "-dia. boss clamped in the chuck, the (now) single 1.850 "-dia. boss on the other end of the part was turned to a 1.765 " diameter for a length of 1.653 ", using a DNMG 431 insert run at 700 rpm and 0.008 ipr. The same tool then faced the remaining stub of the boss removed earlier. Farrington said the part’s eccentric shape posed no problem in the lathe. “It was a pretty good size diameter to hold on to and we didn’t spin it at very high rpm.” A NTF2R threading insert then cut an M45×1.5 thread at the end of the boss.
Next, a 15⁄16 "-dia. drill, applied at 400 rpm and 0.010 ipr with a 0.250 " peck cycle, drilled the boss to a depth of 9.665 ". A 1 "-dia. KMT boring bar run at 500 rpm and 0.007 ipr finished the bore to a diameter of 1.37 ", ±0.002 ".
The part then was turned end to end in the lathe and chucked on the 1.850 "-dia. boss, gripping behind the thread. A 13⁄16 "-dia. drill made a 2¼ "-deep hole in the 2.100 "-dia. boss at 500 rpm and 0.005 ipr, employing a 0.250 " peck. Then a 5⁄8 "-dia. boring bar created a chamfer and a counterbore in the hole’s front end and behind that cut a bearing diameter of 1.0004 ", ±0.0004 ".
For the final operation, the housing was clamped horizontally in a Haas indexer mounted on the VMC’s table and again held on the 1.850 "-dia. boss. A ½ "-dia. carbide endmill, run at 2,000 rpm and 18 ipm, milled a series of lengthwise flats, positioned via the indexer at 10° intervals. Then, the same endmill circular interpolated two 0.775 "-dia., 0.354 "-deep counterbores in the end of the 2.100 "-dia. boss. After machining, the housing received a 0.005 "- to 0.010 "-thick blue anodized coating.
Total machining time for each part was about 90 minutes. Farrington termed this five-piece job a typical, small-volume prototype job, involving ongoing consultation with the customer’s engineers as the design evolved during the prototyping process.
For more information about John Prosock Machine Inc., call (215) 804-0321 or visit www.jprosock.com.
Related Glossary Terms
- bandsaw
bandsaw
Machine that utilizes an endless band, normally with serrated teeth, for cutoff or contour sawing. See saw, sawing machine.
- boring
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.
- chuck
chuck
Workholding device that affixes to a mill, lathe or drill-press spindle. It holds a tool or workpiece by one end, allowing it to be rotated. May also be fitted to the machine table to hold a workpiece. Two or more adjustable jaws actually hold the tool or part. May be actuated manually, pneumatically, hydraulically or electrically. See collet.
- computer-aided manufacturing ( CAM)
computer-aided manufacturing ( CAM)
Use of computers to control machining and manufacturing processes.
- coolant
coolant
Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.
- counterbore
counterbore
Tool, guided by a pilot, that expands a hole to a certain depth.
- endmill
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
feed
Rate of change of position of the tool as a whole, relative to the workpiece while cutting.
- fixture
fixture
Device, often made in-house, that holds a specific workpiece. See jig; modular fixturing.
- gang cutting ( milling)
gang cutting ( milling)
Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.
- high-speed steels ( HSS)
high-speed steels ( HSS)
Available in two major types: tungsten high-speed steels (designated by letter T having tungsten as the principal alloying element) and molybdenum high-speed steels (designated by letter M having molybdenum as the principal alloying element). The type T high-speed steels containing cobalt have higher wear resistance and greater red (hot) hardness, withstanding cutting temperature up to 1,100º F (590º C). The type T steels are used to fabricate metalcutting tools (milling cutters, drills, reamers and taps), woodworking tools, various types of punches and dies, ball and roller bearings. The type M steels are used for cutting tools and various types of dies.
- inches per minute ( ipm)
inches per minute ( ipm)
Value that refers to how far the workpiece or cutter advances linearly in 1 minute, defined as: ipm = ipt 5 number of effective teeth 5 rpm. Also known as the table feed or machine feed.
- lathe
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.
- machining center
machining center
CNC machine tool capable of drilling, reaming, tapping, milling and boring. Normally comes with an automatic toolchanger. See automatic toolchanger.
- milling
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.
- milling machine ( mill)
milling machine ( mill)
Runs endmills and arbor-mounted milling cutters. Features include a head with a spindle that drives the cutters; a column, knee and table that provide motion in the three Cartesian axes; and a base that supports the components and houses the cutting-fluid pump and reservoir. The work is mounted on the table and fed into the rotating cutter or endmill to accomplish the milling steps; vertical milling machines also feed endmills into the work by means of a spindle-mounted quill. Models range from small manual machines to big bed-type and duplex mills. All take one of three basic forms: vertical, horizontal or convertible horizontal/vertical. Vertical machines may be knee-type (the table is mounted on a knee that can be elevated) or bed-type (the table is securely supported and only moves horizontally). In general, horizontal machines are bigger and more powerful, while vertical machines are lighter but more versatile and easier to set up and operate.
- reamer
reamer
Rotating cutting tool used to enlarge a drilled hole to size. Normally removes only a small amount of stock. The workpiece supports the multiple-edge cutting tool. Also for contouring an existing hole.
- tap
tap
Cylindrical tool that cuts internal threads and has flutes to remove chips and carry tapping fluid to the point of cut. Normally used on a drill press or tapping machine but also may be operated manually. See tapping.
- threading
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.
- tolerance
tolerance
Minimum and maximum amount a workpiece dimension is allowed to vary from a set standard and still be acceptable.
- 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
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.
Author
News items authored by Cutting Tool Engineering have been written or edited by the editors of Cutting Tool Engineering magazine. The reports represent material submitted to CTE by outside authors, and edited by CTE editors for style and accuracy.
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