The usual suspects

Let’s review some basics. I dig into the details a bit more over the next few pages, but be aware that a “typical” machine shop is filled with lathes and mills. These may be powered by a human being that turns handles and pulls levers (which makes them, appropriately enough, manual machine tools). More likely, they may be powered by servomotors and controlled by a computer, giving then the lofty term, computer numerical control (CNC) machine tools.

The toolroom in a stamping house or indeed in any sheet-metal fabricator is a bit unlike the typical job shop I was just getting all gushy over. For one thing, you’re likely to see more manual equipment. That’s because activities like fixture building and punch sharpening are often easier on a hand-cranked machine, with none of that pesky CNC programming and coordinate setting required by automated machine tools.

Some shops might disagree with the previous statement. That’s because a properly equipped CNC lathe or machining center can be every bit as efficient on low-quantity production and prototype work as a manual machine. Quick-change workholding eliminates the need for setting coordinate systems. Offline tool presetting avoids having to “touch off” cutting tools. Computer-aided manufacturing (CAM) systems and toolpath simulation software makes proving out a machine program as difficult as pushing cycle start. If your toolroom isn’t leveraging these technologies, you’re missing the boat on improved efficiency.

I’ll take the combo

A fab shop may also include more “half CNCs,” or combo machines, similar to the one shown in Figure 12-1. These are a best-of-both-worlds solution to those not yet ready to purchase or unable to justify the greater expense of a full-blown CNC machine. They can be operated manually by turning the cranks as you would on your toolroom lathe or knee mill, or programmed with a CAM system not unlike the one used to program your punch press. They can even be “taught” how to machine parts, similar to the teach mode used to program many robots (cruise back to the previous chapter if you need a refresher).

The beauty of these machine tools is their lower cost (perhaps half that of a production CNC machine), their ease of use for those unfamiliar with CNC equipment (many old-timers are reluctant to operate them), and their ability to automate tasks that can be challenging to do manually, such as single-point threading and machining bolt hole patterns. Add it all up and combo machines are a flexible machining solution for many tool and die departments.

Facing the hard facts

Toolrooms are also likely to have more grinding and EDM equipment, which are generally more suited to holding the close tolerances called for in stamping dies and other sheet-metal tooling. The same can be said for the hardened tool steels and carbide used to make much of that tooling — most of the time, the best way to machine it is with EDM and grinding, which scoffs at ultra-hard materials.

Justifying their existence

I said it earlier: Nothing happens without tools. In the case of sheet-metal fabrication — whether it’s stamping or bending or punching — those tools are the die shoes, jigs and fixtures, punches and dies, and all the miscellaneous pins, bolts, and other hardware that goes with them. In all honesty, many of these items are purchased off-the-shelf and assembled into whatever turret or bolster plate needs them. But ask anyone who’s worked in a shop: Special tooling requirements are always popping up, and more often than not they are needed that afternoon.

Toolrooms do far more than put out fires, however. Many are fully-equipped machine shops in their own right, able to compete with darned near any production house around. This is a great example of vertical integration. It’s more than a catchy marketing term. “Going vertical” means mastering sheet-metal processing and machining alike, and may also mean taking on secondary finishing processes such as powder coating, painting, and assembly. (I flesh out the first two of those processes in Chapter 15.)

Vertical integration gives your customers “one throat to choke” when procuring manufactured parts. It shortens lead times, and because shops are forced to own each step in the manufacturing process, it often improves quality. And because parts aren’t being shipped all over town to different specialty shops, costs are reduced.

The moral of the story is this: The most successful shops are (or soon will be) those that embrace all types of metalworking, including machining and finishing. Keep that in mind if you’re just getting started in fabricating, as it may alter the path of your education.

Turning terrifically

Because I’m an old lathe guy, I’ll begin there. Lathes make round parts through a process called turning. (Although, some misguided souls refer to it as lathing. Please be polite when correcting them.) The screws that hold your Xbox case together were turned. So too were those annoying dowel pins in your IKEA furniture, the washers you’re using to shim the corner of the coffee table, and the candlesticks you gave to Mom for her birthday.

In a toolroom, lathes might be used to rough and semi-finish a punch for a stamping operation. In most cases, these would go on to a cylindrical grinder for finishing after heat treatment, although an increasing number of shops are turning (pun intended) to hard turning with cubic boron nitride (CBN) and ceramic cutting tools. (Scope out Figure 12-2 for a quick visual.)

Other ways a lathe might be put to use include turning shafts and retaining pins, threading bolts and other fasteners, boring bearing housings, and so on. Simply put, if it’s round, it probably spent time on a lathe. Here are some of the different kinds of lathes you’re likely to encounter during your manufacturing journey:

• Engine lathes: They don’t make engines, nor do they contain one, although some of the earliest lathes (and indeed most machine tools) were connected via a series of belts and pulleys to a steam engine, hence the name. Today’s engine lathes are characterized by a carriage that moves longitudinally, on top of which rests a cross-slide for radial-type work such as cutting a workpiece to length, and a compound rest that’s used for cutting tapered part features and for single-point threading.
• Toolroom lathes: A toolroom lathe is a lighter duty, more accurate version of an engine lathe. It too employs a gearbox and leadscrew that can be used to single-point threads and power the slides, and like an engine lathe, has a tailstock and live center to support long workpieces. You can also take the live center out of the tailstock and replace it with a drill bit for making holes in the end of the workpiece.
• CNC lathes: Unlike most manual lathes, CNC lathes have a turret mounted on top of the slide arrangement that can accommodate multiple turning tools. This eliminates the need to stop the machine when switching from a drill to a threader or cutoff tool, for example, and allows continuous execution of the CNC program (called G-code). Some are equipped with “conversational” controls that eliminate the need for offline programming systems (most combo machines boast conversational programming capabilities, making it easy to program the machine on the shop floor).

This list is nowhere near complete. Many machine shops use Swiss-style screw machines to turn very small and/or long, skinny parts. Live-tool lathes have milling attachments that allow features such as slots and cross-holes to be machined, eliminating secondary operations. Multispindle lathes, as the name suggests, turn multiple parts simultaneously. Multitasking lathes have a machining center-style spindle for milling operations and may have a sub-spindle for turning the back side of a workpiece. That said, the three types of lathes listed earlier represent the typical lathes found in typical toolrooms in typical fabricating shops everywhere. How typical.

I may have misled you, dear reader, when I mentioned the various household uses of washers and screws a couple paragraphs back. Those parts probably weren’t turned. They could have been, but when making gazillions of them for the likes of IKEA or Ace Hardware, manufacturers rely on the most cost-effective production method. For washers, this is stamping. Pick one up and you’ll see — the edges on one side are slightly rounded, while those on the opposite side are slightly sharp. These are the telltale signs of a stamped metal part. As for the screws, they were probably cold-headed, a process that uses metal wire and a forming die to crank out fasteners faster than a first-date kiss with the minister’s daughter.

Milling majestically

You may have noticed the seemingly interchangeable terms milling machine and machining center graffitied across the preceding pages. Sorry for the confusion; the two aren’t interchangeable. I mean, feel free to call them whatever you want, but mill, knee mill, milling machine, and especially Bridgeport (even those that aren’t actually made by that oft-imitated company) all refer to a hand-cranked machine tool invented more than 80 years ago (see the eminently important historical sidebar “Cutting it up in Connecticut”).

Machining centers, on the other hand, are by definition CNC machines. Most have three axes of motion (X, Y, and Z) and a spindle that is oriented vertically, hence the name vertical machining center (VMC). Accessorizing one with an “indexer” is no big deal (it looks sort of like the lazy Susan on your kitchen table, but tipped up sideways), giving operators access to multiple sides of the workpiece in a single handling.

Similarly, a rotary table (also known as a “4th axis”) allows complex shapes like turbine blades and gears to be machined (see Figure 12-3). And as with the turret on a CNC lathe, VMCs are equipped with carousel or magazine-style automatic tool changers (ATCs), providing non-stop machining.

Spinning ’round: Rotary tools

Generally speaking, rotary cutting tools such as end mills and slitting saws are associated with milling operations. In this case, the tool spins while the workpiece moves past it, thus allowing the cutter to shave away material as it passes. Here are a few examples of the most common rotary tools:

• Drill bits: Holemaking is the most common of all metalworking operations, and aside from the holes made with laser or electron beams (a surprising number), most are drilled with a drill bit. It should therefore come as no surprise that so many different types of drill bits exist, everything from Jobbers and screw machine–length to indexable, center, and spade drills. Most resemble pencils, but with a flatter point (usually with an included angle ranging from 118 to 140 degrees) along with a chisel-like cutting edge and no rubber eraser. Drills with two “flutes” are the most common (these are spiral, barber pole–like grooves running along the outside), but three-fluters (which offer higher penetration rates and straighter holes) are also available.
• Reamers: Drill bits leave much to be desired in terms of surface finish and hole quality; reamers are often used to improve both. These are multi-fluted cutting tools that remove a relatively small amount of material, straightening the hole and smoothing the walls as they pass. The most common is a chucking reamer, although hand reamers, fluting reamers, machine reamers, and others are also available. Adjustable reamers are particularly useful in a toolroom, allowing the operator to turn a small screw to tweak the hole size when the tool wears.
• End mills: An end mill looks much like a drill, except the end is usually square or round rather than pointed. Two- to four-flute versions are most common, although some manufacturers have introduced five-flute, seven-flute, and even eleven-flute end mills. Despite their being kissing cousins to drill bits, end mills are designed to cut radially (side to side), “interpolating” part features such as pockets and slots. That said, center-cutting end mills do offer limited drilling capability and can also be made to “tornado” into a workpiece (called helical interpolation), tracing a circular toolpath while simultaneously driving into the workpiece longitudinally.
• Threading: Next to holemaking, threading is one of the most commonly performed of all metal-cutting operations. Most often it’s done with a tap, a tool shaped like a bolt or screw but with two or more thread-cutting flutes running along its length. On a CNC machine, the spindle’s linear motion must be precisely synchronized with its rotation so as to avoid breaking the tap or stripping the threads, but on a manual machine, the tap is often floated into a pre-drilled hole by feel. Also on CNC machines, many threads are now generated using a special thread-cutting end mill and helical interpolation called — appropriately enough — thread milling.

The list goes on and on. Face mills are used to machine the top surface of a workpiece. Shell mills are soup can–shaped end mills with no end-cutting capability used to cut shoulders and slots. Mold makers use button cutters to rough out pockets. Slotting cutters and slitting saws cut slots. Corner-rounding end mills cut neat radii along the top edge of a workpiece to make it look pretty.

Most rotary cutting tools are available in solid carbide, high-speed steel, and “indexable” versions, the last of which has little chunks of precision-ground carbide attached to steel bodies that are recycled when dull. These offer the lowest “cost per edge,” an important consideration for most shops, but are not as effective as tools made of solid carbide. It’s for this reason that most milling cutters around 1/2 inches and smaller are carbide, while larger cutters are usually indexable (see Figure 12-4).

Hold still: Stationary tools

Contrast this with turning operations, where the tool is held stationary and the workpiece itself spins. Take a peek inside any CNC lathe. There you’ll find a turret filled with “stick tools” that have square shanks and a carbide insert on one end much like those found on an indexable milling cutter. Of course, you’ll see drill bits, reamers, and taps there as well (though not rotating), since a big percentage of turned parts have holes and threads in them.

In no particular order, here are the most commonly used turning tools:

• Boring: Once a hole has been drilled, it often needs to be enlarged or otherwise finished. I mention reamers earlier in this chapter, but these are just one piece of the hole-finishing puzzle. Boring tools can be used to cut counterbores. They might be programmed to trace a complex internal shape or used to cut a bore for which a reamer is unavailable or inappropriate. Boring tools are also used on milling machines and machining centers but require an adjustable boring head and can only be used to cut straight holes — no contours or profiles allowed.
• Grooving: Grooves are a common part feature, used to contain rubber O-rings and seals, snap rings to hold a mating component in place, or to “relieve” the groove’s adjacent diameter, effectively creating a sharp inside corner when placed against a shoulder. Grooving tools can be classified as external, internal, or face groovers (an operation referred to as trepanning). Because of all the different widths, shapes, and depths, never mind the universe of workpiece materials, grooving inserts galore exist. Some groovers are designed as “parting tools” that are used to cut finished parts from a length of bar stock clamped in the lathe chuck.
• Profiling: No, I’m not talking about the politically-charged type of profiling, but rather the kind used to turn the outside of a shaft. Profiling inserts (most folks just call them turning tools) are available in various square and parallelogram shapes (that is, diamonds) and are responsible for the lion’s share of metal removal during turning operations. Turning and facing a shaft, for example, might use an 80-degree, 55-degree, or 35-degree diamond insert, the difference being the included angle of the cutting edge.
• Threading: Internal threads are most often tapped, but bolts, fasteners, and other parts with threads on the outside are usually “single-pointed” using V-shaped threading inserts (this can be done on larger internal threads as well). As with tapping, synchronization between the spindle motor and axis motion is required — on a CNC machine, the computer and its servo systems take care of this, but on an engine or toolroom lathe, a gear arrangement drives the carriage at the precise rate needed to cut the thread.

This section on lathe tooling has thus far only mentioned indexable tools, but back in the day, lathe machinists used square blocks of sharpened high-speed steel, or “brazed” tool bits with little pieces of carbide welded on top. These are still available and there may be plenty of shops still using them, but doing so is a monumental waste of time and money (sorry for offending anyone). There’s simply no reason not to embrace indexable lathe tooling, as well as other modern cutting-tool technologies, whether they’re used on a spanking-new CNC machine or the oldest, ugliest engine lathe in the shop.

Sink or swim

Also known as ram, cavity, and conventional EDM (see Figure 12-5), sinkers use an electrode that’s been previously machined into a mirror image of the desired workpiece shape. It’s an ideal way to machine injection-mold cavities, coining dies, and complex shapes in workpieces that cannot be produced via conventional means — square internal corners in a workpiece, for example, or tiny recesses too small or deep for a cutting tool.

Aside from the high-frequency stream of sparks common with all EDM tools, sinkers also employ “orbiting” to remove metal. In this case, the electrode is plunged into the workpiece using a reciprocating up and down motion, and then moved around to shape the cavity, often in multiple axes simultaneously. This provides improved size control over plunging and allows even simple electrodes to make complex shapes.

Wired up

Instead of a previously-machined graphite, copper, or tungsten electrode, wire EDM (WEDM) uses a spool of consumable wire — the electrode — that passes through a tortuous series of wheels and rollers, over an electrical contact, through a doughnut or V-shaped guide, through the workpiece into another set of guides on the opposite side, across an opposing contact point, and onward to a waste bin or take-up reel for disposal of the now spent electrode (see Figure 12-6).

WEDM’s primary role is punch and die–making, but it can also be used to cut slots, grooves, holes, and irregularly-shaped features in everything from medical parts to spline gears. Workpiece tapers up to 45 degrees or so can be produced, as can curves more sweeping than a modern art exhibition. The beauty of wire EDM, and indeed all EDM processes, is its ability to cut very hard materials with impunity. WEDM is also extremely accurate, able to hold tolerances of +/- 0.0001 inches (0.002 mm) or better and surface finishes smoother than the proverbial baby’s bottom. And because the electrode used with “traveling wire EDM” (an old term that’s rarely used anymore) is very thin — about 0.008 inches, give or take — material waste is extremely low.