Machine Shop Operations

03-01-2002  Rev. 2003-09-19, -09-23
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This is not intended as a replacement for the Machinists Handbook, but as an intro to the tools and operations of a small machine shop as might be used by a glass worker. Glossary of Shop Tools and when they are used

Drilling a hole Tapping a hole Threading with a Die  
Welding Braising Soldering  
Cutting Metal Sawing Torching Shearing
Plasma Cutting Laser Cutting Abrasive Cutting Bending





Drilling a hole
Drilling a hole involves rotating a bit to cut out material with the end of the bit and make a smooth cylindrical hole part way or all the way through the material. Different bits are used with different materials: wood, metal, plastic, glass, ceramic, stone/concrete.
Bits have different ends and are primarily round with spiral grooves to clear the cut material or flat used only with soft material - wood or plastic.
The bit may be turned with a motor or by hand.  It is held by a chuck or collets.  These permit various bits to be used in the more expensive hardware.  Collets are more precise but each one has a very limited range of adjustment.
The motor drive may be a battery powered screwdriver, a hand-held, geared-down motor in a pistol shaped housing powered by a battery or AC power, or a larger AC motor belt driving a moveable head - a drill press. The best results (straight hole in the right position) with the material clamped to the platform of a drill press, but this is not always necessary or possible.
Hand drive of drill bits is possible, usually in a tool that speeds up the turning of the bit from the hand motion, but hand held drilling is likely to be uneven from wobbling.
When drilling metal it is best to use a center punch to mark the starting point and make an indentation to catch the end of the bit.
Tapping a hole
Tapping is the process of placing threads inside a hole so that a bolt or pipe with matching threads may be placed and held in the hole. Cutting fluid is required. The tap is a long slender tool like a drill bit, but with teeth on the side. Taps may be tapered, for more easily starting threads, or square ended, for cutting to nearer the bottom of a hole (bottoming tap). The handle is a T-shape with a chuck. During tapping, it is common to have to turn the tap in and then back out to break off shavings and clear the area next to the teeth. The greatest skill in hand tapping is learning when not to lean harder on the tap, and thus break it.
A simple use for a tap is to clean up threads that have become damaged, by carefully turning it into the hole. Of greater interest is putting threads in holes so that nuts do not have be used, thus reducing projections and/or making narrower or cleaner tools or fittings.
In the image below are examples of two tapping handles and a tap (top center and left). The top left hand tap handle has an adjustable T-handle that can be pushed to one side for clearance and has a ratchet mechanism to permit use in tight quarters. The tap is held by a chuck with v-jaws. The center handle with the V-slot will handle bigger taps but only where there is clearance. The tap (top center) has a square end for gripping in the handles and then a smooth portion which has printing to identify the tap and often the drill needed. The threaded portion has clearance grooves for the chips taken out. This is a plug tap, which tapers at the end to fit in the drilled hole before cutting the threads. A bottoming tap is square on the end and has full threads to the end to cut to the bottom of a hole. (A tapered tap is one for tapered holes, as in plumbing connections, full threads down a taper.)

Taps and Dies example

The handle in the center bottom takes dies like the one above it to the right, a 1" hexagon die. The die fits in the handle and is held by the set bolt on the side. Clearance is assumed. Other die holders exist which fit in a brace and drive the die from behind. When larger material is to threaded, much more massive handles are required and the system for threading larger pipe involves three section dies, a head several inches across, and a 2-3 foot long handle. Parts for this cost several dozen dollars each vs. a couple of dollars for hex dies.
The cutting fluid to the right in the picture is vital for taps and dies and very useful for drilling and cutting metal. Often called cutting oil, more correctly called cutting fluid, it serves several functions, cooling the fine teeth doing the actual cutting and keeping the bits of metal from welding to the teeth. It provides some lubrication and carries off trash bits if used liberally. (There is another cutting fluid mixed with cooling water for large cutting operations, as on a lathe.) It is hard to explain to some people why an "oil" is used in cutting, "Doesn't that just make the blade slip?", but cutting is not grinding - an abrasive action - it is cutting, the edge of the teeth is getting into the material being cut and digging out bits, more or less together.
Threading with a Die
Threading is making grooves on the outside of tubing or rod that match the threads tapped inside a hole or inside a nut. Most glass workers will thread using hexagon shaped dies that are held in a holder with handles (above). One side of the die opening is bigger than the other and the metal enters that side. The holder may have adjustable guides to center the metal in the opening.
Threading with a Lathe
Rarely done by the amateur worker, it is possible to cut threads inside or out on a machinist's lathe equipped with a drive for the tool holder that moves it a precise amount for each turn of the work, so the tool cuts a groove. The shape of the tool makes the shape of the thread, which may be a V or a U or flat bottomed.
Welding is the process of heating metal until some of it melts, forming a solid bond between closely places pieces. Welding may be done with an electric arc or a torch.
Torch welding is considered more difficult by some, but it is quieter and less exciting in stuff thrown about.  A torch combines gas from a regulated acetylene tank and oxygen from another regulated tank and produces a small very hot flame which is used to create a puddle of molten metal which is moved along the joint.  A thin welding rod may be used to add material. A special torch head can be used to cut steel and another to provide broader heating.  Besides steel, lead and aluminum may be welded (with care) usually with other gases.
Arc (electric) welding is done with a power supply that converts wall electricity (higher voltage) to high current, lower voltage.  A thicker rod or wire conducts the current to work piece which completes the circuit.  When the conductor is touched to the piece and pulled back, an arc forms which is brilliant and hot.  The heat melts the end of the rod/wire and the work piece and the melted material flows together.  Very good eye protection is required for arc welding and onlookers must be protected also.  Normally a lot of sparks are thrown, so the area must be flame resistant for many feet around.  When wire is used, it is automatically fed and commonly is surrounded by inert gas to make welds in materials that don't take welding with a larger rod or torch all that easily - like stainless steel or aluminum.  MIG welding is metal in gas and the wire is related to the material being welded.   TIG is tungsten in gas and the wire is tungsten and is used up much less rapidly.  Lower cost MIG welders are available to run off household current and may be rented.
Braising is the process of heating another metal than that of the piece at a higher temperature than soldering but lower than welding, so that the added metal forms a hard, strong bond with the base metal.  Some materials that can not be welded can be braised - cast iron for example.  A common braising material is brass.  Because it is done with a metal that melts below the base metal, that places an upper limit on the temp the joint can be exposed to - most will fall apart at glass working temps.  Depending on the amount of metal involved, braising can be done with an especially hot propane/air torch (braising torch), with propane/compressed air, propane/oxygen, or oxy/acetylene.  Braising equipment can be less costly than welding and requires less eye protection.
Soldering is the joining of metals at relatively low temperatures.  Solder typically melts at 300-600F vs braising rod melting at 1200F or more. Copper, brass, and tin are easiest to solder and may be done with an electric iron, electric gun, or small torch.  Silver soldering is between braising and soldering in temperature range, depending on the solder.
Cutting Metal
Metal rod, flat, pipe and tubing is most commonly cut by sawing with a thin blade with fine teeth.  A short length of this blade can be mounted in a frame, called a hack saw, and pulled and pushed by hand or by motor.  Smoother is to have a long length of blade welded into a loop and mounted on a pair of wheels, called a band saw.  A metal band saw may be a rigid upright unit, similar to those used for wood, or it may be mounted on a pivot so the weight of the head presses the blade into the metal.  Portable metal cutting band saws and circular chop saws using abrasive or special diamond cutting blades also exist. 2006-02-13
Large flat sheets of metal are commonly sheared.  The tool may be hand shears like large scissors in special shapes to help deal with the stiffness of metal compared to paper or cloth. A shop doing a lot will have a very heavy expensive machine, a shear, that can cut up to 1/2" thick sheet.  More commonly, a shop's shear handles sheet 1/16" (16 ga) or less, but it still needs to be a substantial machine to span the 48 to 96" of a full sheet.  For glass workers, a solution is to buy the metal sheared to size, and perhaps bent, at a higher cost of course, with welding and assembly done by the worker.
Large heavy pieces of metal may only be cut with a cutting torch.  The torch does two jobs - it heats a local spot to considerable temperature then adds a lot of oxygen so the chemical heat given off by iron, carbon, and oxygen and the blast produces enormous showers of sparks that carry off the metal and leave a cut.  Especially if the torch is mechanically moved, the cut can be very narrow and cut inches thick metal.  Hand cutting often leaves slag that holds the cut.
Plasma Cutting
If gas is heated electrically with an arc, it can be used for cutting relatively thin metal which it can do very precisely, especially under computer control.  Because the equipment is lighter, it can be used by hand and costs less.
Laser Cutting
Laser light is a special form that allows control of a lot of energy to in a very small area.  Under computer control, it will cut very fine lines in metal and other materials such as plastic and laminates.  High power lasers require a lot of electricity and support mechanism, so are costly.  No hand unit exists.
Abrasive Cutting
If a fine stream of abrasive is added to liquid under very high pressure shot through hole in a hard material like sapphire, it can cut very fine lines in material that is very brittle, like glass and stone, or soft like fabric, paper, or copper.  The cutting velocity is so high, the water normally passes through without seriously wetting the material.  The force of the blast requires a strong structure both over and under the material.
Various forms of metal are bent with various special tools.  Flat sheet is bent in a brake which holds the metal tight and creates very crisp corners.  The tool has slots to allow flanges to have tight corners also.  Like a shear, a brake must span the metal and be stiff, thus heavy.  Again, having the shop selling the sheet metal do the preliminary bending can save the glass worker effort with a crisper look.  Tubing has special bending tools using wheels to form curves.  Sheet can be formed into smooth curves with English wheels and other tools.
While it is possible to buy most metal working tools needed in the glass worker's shop at a reasonably good hardware store or at Sears, Lowes or Home Depot, one substantial source is MSC which has a very thick catalog of machine tools and materials and an online site MSC Industrial Supply Co. The site is beautifully designed and although it appears to require signing in (which you would have to do to buy) searching is available and educational.
AC Power
The power obtained from a wall outlet. Alternating current. Batteries supply direct current. The amount of power (amps or watts) available is limited by the protective circuit breakers and the size wire and length of any extension cords used.
Allen Wrench or Drive
A six sided (hex) drive in the form of a small hole in flat bottom and six sides.  Used on a variety of small bolts including set screws.  Permits a smoother top surface than a slot or Phillips
Belt V-Belt
A belt drive tool has rubber belts with fabric inside to reduce their stretching which fit in the grooves of round pulleys, one or more on the motor and matching one(s) on the driven shaft. The sides of the belt are angled so they are called V belts. Common uses are drill presses, grinders, and accessories (the water pump) in cars.  Belt drive can also be done with belts that have bumps on them that match notches in the pulleys, more often used for timing belts.
Part of a tool for cutting. A drill bit rotates and cuts on the end. A router bit rotates and mostly cuts on the side. A lathe bit is held steady and end cuts into rotating material. Drill bits come in a number of forms, some of which (paddle) can only be used on wood, others (twist) can be used on either and the kinds of metal in the bit determines what can be drilled.
A device for holding rotating work or bits. Jaws mounted in or on a round body move in and out to grip the work or tool. A drill has one for holding bits that encases the bit body and keeps it aligned and centered while drilling is done. A lathe has one that grips part of the work and is much bigger and open. Collets 2006-03-13
Alternative to a chuck, used for holding tools with precision, typically a cylinder with several grooves cut lengthwise, which a squeezed shut by a nut to grip a bit, so limited size adjustment.  Seen in routers, high speed grinders, and metal working machines. 2006-03-13
Verb: to drill or cut the top of a drilled hole so that the head of the fastener is at or below the material surface. The shape of the hole matches the shape of the fastener - cylindrical or cone shaped.
Noun: the tool used for countersinking that produces a V shaped top to the hole so that the matching V bottom on the fastener fits in.  Cylindrical countersinking is done with a larger drill bit. 2006-03-13
Cutting Fluid (or Cutting Oil)
When cutting metal, a fluid assists by keeping the bit and metal cooler and preventing welding of the two together from too much heat or damaging the bit by overheating. Sometimes called cutting oil, this is misleading because it is not a lubricant.
Shape where the work is done inside, thus a threading die has cutting teeth inside and a forming die has the shape inside.
Flat Head
A screw head that is cone shaped on the material side and flat on the visible part, usually countersunk so the flat head is flush with the surface. Other heads include round head (1/2 a sphere), pan head (flat top, rounded corners, like a fry pan), button, fillister, hex, etc. Amateur tool people worry that when they say flat head, they will be thought to be talking about heads that are flat on the bottom, so they start talking about the cone underneath.
Enlarged part of a fastener - nail, bolt, rivet, screw - that holds one piece of material to another.  After the image of the head of a skinny person in profile.  Either the outer edge is shaped for a tool - hex head - or a slot, hole or other shape is provided within the head - slotted, Phillips, Allen, square drive.  Described by shape - hex head, cap head, flat head. 2006-03-13
Hex Head
Six sided fastener head that may be turned with a socket wrench from above or an open end or hex wrench from the side. 2006-02-13
A tool that rotates a piece of material, wood or metal usually, while a bit or chisel cuts into the side (usually) Most commonly, the work is supported at both ends, driven by a motor at one end, with the cutting tools resting on or held in devices attached to a bed that keeps all the parts aligned during adjustment. Most lathes can also work with a piece just attached or chucked to the motor head.
a type of slot in the top of a screw looking like a plus + sign.  Designed to grip a driver better than a slot.  Square drive (Robertson) has superceded it in wood working screws. 2003-09-23
The distance from one peak of a wave or thread to the next. Metric bolts are specified by pitch - 1.50 pitch is one and a half millimeters from peak to peak. American thread is usually given in threads per inch - so 20 threads per inch would be 0.05" pitch. Conversion is just dividing the unit of measure into the pitch or or dividing the unit by the parts per unit.
A long slender hard metal tool intended to be struck with a hammer on one end to make a mark or drive out something with the other end. A center punch has a cone shaped end for marking. A nail set pushes nail heads down to or below the surface. A long slender punch can be used to force a pin out of a hole.
A device, most often used for fastening or clamping, with threads around its length to pull the device forward when turned. Wood and sheet metal screws have tapered threads, machine screws cylindrical.  Threads Threading 2006-03-13
Set Screw
A short threaded cylinder with a hard point or circle that is used to hold a device - pulley or collar - on a shaft.  Often driven with a hex - Allen - wrench, it is a small headless bolt. 2003-09-23
A tool with teeth on the sides to thread the inside of a hole.
Threads are grooves spiraling around a tube, rod or hole. Threads are specified by the diameter of the root of the thread, the number of threads per inch (or metric pitch) and the shape of the thread. Often the shape is assumed and not mentioned. Thus 1/4 - 20 is a common bolt thread, one-quarter inch diameter by 20 threads per inch with V grooves. For various reasons, threads used to position machinery or clamp are normally flat bottomed and flat sided. There are systems of threads that are similar in shape and progress regularly in size - in America, pipe threads (1/4" NPT), common threads (1/4 -20, etc.) and SAE (1/4 -28) are most often found. More and more we are seeing metric threads (6 - 1.50) which are finer than SAE, which are finer than common threads. Metric threads are sized by the diameter in millimeters and the pitch in millimeters.  All cars built or sold in the U.S. since about 1990 have metric bolts. Threading 2006-02-13
Tool for turning fasteners with special matching shapes or for gripping the outside of material.  A monkey or pipe wrench is used for gripping pipe for turning.  Hex head fasteners may be turned by adjustable (Crescent) wrenches, or open end wrenches which grip the flats or socket and hex head wrenches which grip the corners. 2006-02-13

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