Building scientific apparatus, Manuais, Projetos, Pesquisas de Física

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Building Scientific Apparatus covers a wide range of topics

critical to the construction, use, and understanding of sci-

entific equipment. It serves as a reference to a wealth of

technical information, but is also written in a familiar style

that makes it accessible as an introductory text. This new

edition includes updates throughout, and will continue to

serve as a bookshelf standard in laboratories around the

world. I never like to be too far from this book!

Jason Hafner, Rice University, Houston, Texas

For many years, Building Scientific Apparatus has been the

first book I reach for to remind myself of an experimental

technique, or to start learning a new one. And it has been

one of the first references I’ve recommended to new stu-

dents. With valuable additions (e.g. tolerances table for

machining, formula for aspheric lenses, expanded infor-

mation on detector signal-to-noise ratios, solid-state

detectors.. .) and updated lists of suppliers, the newest

addition will be a welcome replacement for our lab’s

well-thumbed previous editions of BSA.

Brian King, McMaster University, Canada

I like this book a lot. It is comprehensive in its coverage of

a wide range of topics that an experimentalist in the phys-

ical sciences may encounter. It usefully extends the scope

of previous editions and highlights new technical develop-

ments and ways to apply them. The authors share a rich

pool of knowledge and practical expertise and they have

produced a unique and authoritative guide to the building

of scientific apparatus. The book provides lucid descrip-

tions of underlying physical principles. It is also full of

hands-on advice to enable the reader to put these principles

into practice. The style of the book is very user-friendly

and the text is skillfully illustrated and informed by numer-

ous figures. The book is a mine of useful information

ranging from tables of the properties of materials to lists

of manufacturers and suppliers. This book would be an

invaluable resource in any laboratory in the physical sci-

ences and beyond.

George King, University of Manchester

The construction of novel equipment is often a prerequi-

site for cutting-edge scientific research. Jack Moore and

his coauthors have made this task easier and more effi-

cient by concentrating several careers’ worth of equip-

ment-building experience into a single volume – a

thoroughly revised and updated edition of a 25-year-old

classic. Covering areas ranging from glassblowing to

electron optics and from temperature controllers to

lasers, the invaluable information in this book is destined

to save years of collective frustration for students and

scientists. It is a ‘‘must-have’’ on the shelf of every

research lab.

Nicholas Spencer, Eidgeno¨ssische Technische

Hochschule, Zu¨rich.

This book is a unique resource for the beginning experi-

menter, and remains valuable throughout a scientist’s

career. Professional engineers I know also own and enjoy

using the book.

Eric Zimmerman, University of Colorado at Boulder,

Colorado

BUILDING

SCIENTIFIC

APPARATUS

Fourth Edition

John H. Moore F Christopher C. Davis F Michael A. Coplan,

with a chapter by Sandra C. Greer

To our families

8

 - FABRICATION MECHANICAL DESIGN AND 

• 1.1 Tools and Shop Processes
• 1.1.1 Hand Tools
• 1.1.2 Machines for Making Holes
• 1.1.3 The Lathe
• 1.1.4 Milling Machines
• 1.1.5 Electrical Discharge Machining (EDM)
• 1.1.6 Grinders
• 1.1.7 Tools for Working Sheet Metal
• 1.1.8 Casting
• 1.1.9 Tolerance and Surface Quality for Shop Processes
  • 1.2 Properties of Materials
• 1.2.1 Parameters to Specify Properties of Materials
• 1.2.2 Heat Treating and Cold Working
• 1.2.3 Effect of Stress Concentration
  • 1.3 Materials
• 1.3.1 Iron and Steel
• 1.3.2 Nickel Alloys
• 1.3.3 Copper and Copper Alloys
• 1.3.4 Aluminum Alloys
• 1.3.5 Other Metals
• 1.3.6 Plastics
• 1.3.7 Glasses and Ceramics
  • 1.4 Joining Materials
• 1.4.1 Threaded Fasteners
• 1.4.2 Rivets
• 1.4.3 Pins - 1.4.4 Retaining Rings - 1.4.5 Soldering - 1.4.6 Brazing - 1.4.7 Welding - 1.4.8 Adhesives - 1.4.9 Design of Joints - 1.4.10 Joints in Piping and Pressure Vessels - 1.5 Mechanical Drawing - 1.5.1 Drawing Tools - 1.5.2 Basic Principles of Mechanical Drawing - 1.5.3 Dimensions - 1.5.4 Tolerances - 1.5.5 From Design to Working Drawings - 1.6 Physical Principles of Mechanical Design - 1.6.1 Bending of a Beam or Shaft - 1.6.2 Twisting of a Shaft - 1.6.3 Internal Pressure - 1.6.4 Vibration of Beams and Shafts - 1.6.5 Shaft Whirl and Vibration - 1.7 Constrained Motion - 1.7.1 Kinematic Design - 1.7.2 Plain Bearings - 1.7.3 Ball Bearings - 1.7.4 Linear-Motion Bearings - 1.7.5 Springs - 1.7.6 Flexures - Cited References - General References - Chapter 1 Appendix
  • 2 WORKING WITH GLASS
    • 2.1 Properties of Glasses
      • Laboratory Glasses 2.1.1 Chemical Composition and Chemical Properties of Some
• 2.1.2 Thermal Properties of Laboratory Glasses
• 2.1.3 Optical Properties of Laboratory Glassware
• 2.1.4 Mechanical Properties of Glass - Glass 2.2 Laboratory Components Available in
• 2.2.1 Tubing and Rod
• 2.2.2 Demountable Joints
• 2.2.3 Valves and Stopcocks
• 2.2.4 Graded Glass Seals and Glass-to-Metal Seals - 2.3 Laboratory Glassblowing Skills
• 2.3.1 The Glassblower’s Tools
• 2.3.2 Cutting Glass Tubing
• 2.3.3 Pulling Points
• 2.3.4 Sealing Off a Tube: The Test-Tube End
• 2.3.5 Making a T-Seal
• 2.3.6 Making a Straight Seal
• 2.3.7 Making a Ring Seal
• 2.3.8 Bending Glass Tubing
• 2.3.9 Annealing
• 2.3.10 Sealing Glass to Metal
• 2.3.11 Grinding and Drilling Glass - Cited References - General References
  • 3 VACUUM TECHNOLOGY
    • 3.1 Gases
      • System 3.1.1 The Nature of the Residual Gases in a Vacuum
• 3.1.2 Gas Kinetic Theory
• 3.1.3 Surface Collisions
• 3.1.4 Bulk Behavior versus Molecular Behavior - 3.2 Gas Flow
• 3.2.1 Parameters for Specifying Gas Flow
• 3.2.2 Network Equations
• 3.2.3 The Master Equation
• 3.2.4 Conductance Formulae
• 3.2.5 Pumpdown Time - 3.2.6 Outgassing - 3.3 Pressure and Flow Measurement - 3.3.1 Mechanical Gauges - 3.3.2 Thermal-Conductivity Gauges - 3.3.3 Viscous-Drag Gauges - 3.3.4 Ionization Gauges - 3.3.5 Mass Spectrometers - 3.3.6 Flowmeters - 3.4 Vacuum Pumps - 3.4.1 Mechanical Pumps - 3.4.2 Vapor Diffusion Pumps - 3.4.3 Entrainment Pumps - 3.5 Vacuum Hardware - 3.5.1 Materials - 3.5.2 Demountable Vacuum Connections - 3.5.3 Valves - 3.5.4 Mechanical Motion in the Vacuum System - 3.5.5 Traps and Baffles - 3.5.6 Molecular Beams and Gas Jets - 3.5.7 Electronics and Electricity in Vacuo - Construction 3.6 Vacuum-System Design and - 3.6.1 Some Typical Vacuum Systems - 3.6.2 Differential Pumping - 3.6.3 The Construction of Metal Vacuum Apparatus - 3.6.4 Surface Preparation - 3.6.5 Leak Detection - 3.6.6 Ultrahigh Vacuum - Cited References - General References - 4 OPTICAL SYSTEMS - 4.1 Optical Terminology - Systems 4.2 Characterization and Analysis of Optical - 4.2.1 Simple Reflection and Refraction Analysis - 4.2.2 Paraxial-Ray Analysis - 4.2.3 Nonimaging Light Collectors - 4.2.4 Imaging Systems - 4.2.5 Exact Ray Tracing and Aberrations - 4.2.6 The Use of Impedances in Optics - 4.2.7 Gaussian Beams
  • 4.3 Optical Components
• 4.3.1 Mirrors
• 4.3.2 Windows
• 4.3.3 Lenses and Lens Systems
• 4.3.4 Prisms
• 4.3.5 Diffraction Gratings
• 4.3.6 Polarizers
• 4.3.7 Optical Isolators
• 4.3.8 Filters
• 4.3.9 Fiber Optics
• 4.3.10 Precision Mechanical Movement Systems - of Optical Components 4.3.11 Devices for Positional and Orientational Adjustment
• 4.3.12 Optical Tables and Vibration Isolation
• 4.3.13 Alignment of Optical Systems
• 4.3.14 Mounting Optical Components
• 4.3.15 Cleaning Optical Components
  • 4.4 Optical Materials
• 4.4.1 Materials for Windows, Lenses, and Prisms
• 4.4.2 Materials for Mirrors and Diffraction Gratings
  • 4.5 Optical Sources
• 4.5.1 Coherence
• 4.5.2 Radiometry: Units and Definitions
• 4.5.3 Photometry
• 4.5.4 Line Sources
• 4.5.5 Continuum Sources
  • 4.6 Lasers
• 4.6.1 General Principles of Laser Operation
• 4.6.2 General Features of Laser Design
• 4.6.3 Specific Laser Systems
• 4.6.4 Laser Radiation
• 4.6.5 Coupling Light from a Source to an Aperture
• 4.6.6 Optical Modulators
• 4.6.7 How to Work Safely with Light Sources
  • 4.7 Optical Dispersing Instruments
• 4.7.1 Comparison of Prism and Grating Spectrometers
• 4.7.2 Design of Spectrometers and Spectrographs
• 4.7.3 Calibration of Spectrometers and Spectrographs
• 4.7.4 Fabry–Perot Interferometers and Etalons
• 4.7.5 Design Considerations for Fabry–Perot Systems
• 4.7.6 Double-Beam Interferometers - Endnotes - Cited References - General References - 5 CHARGED-PARTICLE OPTICS - Optics 5.1 Basic Concepts of Charged-Particle - 5.1.1 Brightness - 5.1.2 Snell’s Law - 5.1.3 The Helmholtz–Lagrange Law - 5.1.4 Vignetting - 5.2 Electrostatic Lenses - Lenses 5.2.1 Geometrical Optics of Thick - 5.2.2 Cylinder Lenses - 5.2.3 Aperture Lenses - 5.2.4 Matrix Methods - 5.2.5 Aberrations - 5.2.6 Lens Design Example - 5.2.7 Computer Simulations - 5.3 Charged-Particle Sources - 5.3.1 Electron Guns - Example 5.3.2 Electron-Gun Design - 5.3.3 Ion Sources - 5.4 Energy Analyzers - 5.4.1 Parallel-Plate Analyzers - 5.4.2 Cylindrical Analyzers - 5.4.3 Spherical Analyzers - 5.4.4 Preretardation - 5.4.5 The Energy-Add Lens - 5.4.6 Fringing-Field Correction - 5.4.7 Magnetic Energy Analyzers - 5.5 Mass Analyzers - Analyzers 5.5.1 Magnetic Sector Mass - 5.5.2 Wien Filter - 5.5.3 Dynamic Mass Spectrometers - Construction 5.6 Electron- and Ion-Beam Devices: - 5.6.1 Vacuum Requirements - 5.6.2 Materials - 5.6.3 Lens and Lens-Mount Design - 5.6.4 Charged-Particle Detection - 5.6.5 Magnetic-Field Control - Cited References
  • 6 ELECTRONICS
    • 6.1 Preliminaries
• 6.1.1 Circuit Theory
• 6.1.2 Circuit Analysis
• 6.1.3 High-Pass and Low-Pass Circuits
• 6.1.4 Resonant Circuits
• 6.1.5 The Laplace-Transform Method
• 6.1.6 RLC Circuits
• 6.1.7 Transient Response of Resonant Circuits
• 6.1.8 Transformers and Mutual Inductance
• 6.1.9 Compensation
• 6.1.10 Filters
• 6.1.11 Computer-Aided Circuit Analysis - 6.2 Passive Components
• 6.2.1 Fixed Resistors and Capacitors
• 6.2.2 Variable Resistors - 6.3 Active Components 6.2.5 Relays
• 6.3.1 Diodes
• 6.3.2 Transistors
• 6.3.3 Silicon-Controlled Rectifiers
• 6.3.4 Unijunction Transistors
• 6.3.5 Thyratrons - 6.4 Amplifiers and Pulse Electronics
• 6.4.1 Definition of Terms - Principles 6.4.2 General Transistor-Amplifier Operating
• 6.4.3 Operational-Amplifier Circuit Analysis
• 6.4.4 Instrumentation and Isolation Amplifiers
• 6.4.5 Stability and Oscillators
• 6.4.6 Detecting and Processing Pulses - 6.5 Power Supplies
• 6.5.1 Power-Supply Specifications - Supplies 6.5.2 Regulator Circuits and Programmable Power
• 6.5.3 Bridges - 6.6 Digital Electronics
• 6.6.1 Binary Counting
• 6.6.2 Elementary Functions
• 6.6.3 Boolean Algebra - 6.6.4 Arithmetic Units - 6.6.5 Data Units - 6.6.6 Dynamic Systems - 6.6.7 Digital-to-Analog Conversion - 6.6.8 Memories - 6.6.9 Logic and Function - 6.6.10 Implementing Logic Functions - 6.7 Data Acquisition - 6.7.1 Data Rates - 6.7.2 Voltage Levels and Timing - 6.7.3 Format - 6.7.4 System Overhead - 6.7.5 Analog Input Signals - 6.7.6 Multiple Signal Sources: Data Loggers - 6.7.7 Standardized Data-Acquisition Systems - 6.7.8 Control Systems - 6.7.9 Personal Computer (PC) Control of Experiments - 6.8 Extraction of Signal from Noise - 6.8.1 Signal-to-Noise Ratio - 6.8.2 Optimizing the Signal-to-Noise Ratio - Boxcar 6.8.3 The Lock-In Amplifier and Gated Integrator or - 6.8.4 Signal Averaging - 6.8.5 Waveform Recovery - 6.8.6 Coincidence and Time-Correlation Techniques - 6.9 Grounds and Grounding - 6.9.1 Electrical Grounds and Safety - 6.9.2 Electrical Pickup: Capacitive Effects - 6.9.3 Electrical Pickup: Inductive Effects - 6.9.4 Electromagnetic Interference and r.f.i - 6.9.5 Power-Line-Coupled Noise - 6.9.6 Ground Loops - 6.10 Hardware and Construction - 6.10.1 Circuit Diagrams - 6.10.2 Component Selection and Construction Techniques - 6.10.3 Printed Circuit Boards - 6.10.4 Wire Wrapä Boards - 6.10.5 Wires and Cables - 6.10.6 Connectors - 6.11.2 Identifying Parts 6.11.1 General Procedures - Cited References - General References - Chapter 6 Appendix
  • 7 DETECTORS
    • 7.1 Optical Detectors
    • 7.2 Noise in Optical Detection Process
• 7.2.1 Shot Noise
• 7.2.2 Johnson Noise
• 7.2.3 Generation-Recombination (gr) Noise
• 7.2.4 1/f Noise - 7.3 Figures of Merit for Detectors
• 7.3.1 Noise-Equivalent Power
• 7.3.2 Detectivity
• 7.3.3 Responsivity
• 7.3.4 Quantum Efficiency
• 7.3.5 Frequency Response and Time Constant
• 7.3.6 Signal-to-Noise Ratio - 7.4 Photoemissive Detectors
• 7.4.1 Vacuum Photodiodes
• 7.4.2 Photomultipliers
• 7.4.3 Photocathode and Dynode Materials - Tubes 7.4.4 Practical Operating Considerations for Photomultiplier - 7.5 Photoconductive Detectors - (Photodiodes) 7.6 Photovoltaic Detectors
• 7.6.1 Avalanche Photodiodes
• 7.6.2 Geiger Mode Avalanche Photodetectors - 7.7 Detector Arrays
• 7.7.1 Reticons
• 7.7.2 Quadrant Detectors
• 7.7.3 Lateral Effect Photodetectors
• 7.7.4 Imaging Arrays
• 7.7.5 Image Intensifiers - 7.8 Signal-to-Noise Ratio Calculations
• 7.8.1 Photomultipliers
• 7.8.2 Direct Detection with p–i–n Photodiodes
• 7.8.3 Direct Detection with APDs
• 7.8.4 Photon Counting - Detectors 7.9 Particle and Ionizing Radiation - 7.9.1 Solid-State Detectors - 7.9.2 Scintillation Counters - 7.9.3 X-Ray Detectors - 7.10 Thermal Detectors - 7.10.1 Thermopiles - 7.10.2 Pyroelectric Detectors - 7.10.3 Bolometers - 7.10.4 The Golay Cell - 7.11 Electronics to be Used With Detectors - 7.12 Detector Calibration - Endnotes - Cited References - General References - TEMPERATURE MEASUREMENT AND CONTROL OF - 8.1 The Measurement of Temperature - 8.1.1 Expansion Thermometers - 8.1.2 Thermocouples - 8.1.3 Resistance Thermometers - 8.1.4 Semiconductor Thermometers - Thermometry 8.1.5 Temperatures Very Low: Cryogenic - 8.1.6 Temperatures Very High - 8.1.7 New, Evolving, and Specialized Thermometry - Thermometers 8.1.8 Comparison of Main Categories of - 8.1.9 Thermometer Calibration - 8.2 The Control of Temperature - 8.2.1 Temperature Control at Fixed Temperatures - 8.2.2 Temperature Control at Variable Temperatures - Cited References - General References - Index

MECHANICAL DESIGN AND FABRICATION

Every scientific apparatus requires a mechanical structure,

even a device that is fundamentally electronic or optical in

nature. The design of this structure determines to a large

extent the usefulness of the apparatus. It follows that a

successful scientist must acquire many of the skills of

the mechanical engineer in order to proceed rapidly with

an experimental investigation.

The designer of research apparatus must strike a balance

between the makeshift and the permanent. Too little initial

consideration of the expected performance of a machine

may frustrate all attempts to get data. Too much time spent

planning can also be an error, since the performance of a

research apparatus is not entirely predictable. A new

machine must be built and operated before all the short-

comings in its design are apparent.

The function of a machine should be specified in some

detail before design work begins. One must be realistic in

specifying the job of a particular device. The introduction

of too much flexibility can hamper a machine in the per-

formance of its primary function. On the other hand, it may

be useful to allow space in an initial design for anticipated

modifications. Problems of assembly and disassembly

should be considered at the outset, since research equip-

ment rarely functions properly at first and often must be

taken apart and reassembled repeatedly.

Make a habit of studying the design and operation of

machines. Learn to visualize in three dimensions the size

and positions of the parts of an instrument in relation to

one another.

Before beginning a design, learn what has been done

before. It is a good idea to build and maintain a library

of commercial catalogs in order to be familiar with what is

available from outside sources. Too many scientific

designers waste time and money on the reinvention of

the wheel and the screw. Use nonstandard parts only when

their advantages justify the great cost of one-off con-

struction in comparison with mass production. Consider

modifications of a design that will permit the use of stand-

ardized parts. An evening spent leafing through the catalog

of one of the major tool and hardware suppliers can be

remarkably educational – catalogs from McMaster-Carr

or W. M. Berg, for example, each list over 200 000 stand-

ard fasteners, bearings, gears, mechanical and electrical

parts, tools etc.

Become aware of the available range of commercial

services. In most big cities, specialty job shops perform

such operations as casting, plating, and heat-treating inex-

pensively. In many cases it is cheaper to have others pro-

vide these services rather than attempt them oneself. Some

of the thousands of suppliers of useful services, as well as

manufacturers of useful materials, are noted throughout

the text.

In the following sections we discuss the properties of

materials and the means of joining materials to create a

machine. The physical principles of mechanical design are

presented. These deal primarily with controlling the

motion of one part of a machine with respect to another,

both where motion is desirable and where it is not. There

are also sections on machine tools and on mechanical

drawing. The former is mainly intended to provide enough

information to enable the scientist to make intelligent use

of the services of a machine shop. The latter is presented in

sufficient detail to allow effective communication with

people in the shop.

CHAPTER

1

(Figure 1.1) is used in a lathe or vertical milling machine to

bore out a drilled hole to make a large hole. Of course,

a hole can be drilled with a twist drill in a handheld

drill motor; this method, although convenient, is not very

accurate and should only be employed when it is not pos-

sible to mount the work on the drill press table.

Twist drills are available in fractional inch sizes and

metric sizes as well as in number and letter series of sizes

at intervals of only a few thousandths of an inch. Sizes

designated by common fractions are available in 1/64 in.

increments in diameters from 1/64 to 1 3/4 in., in 1/32 in.

increments in diameters from 1 3/4 to 2 1/4 in., and in

1/16 in. increments in diameters from 2 1/4 to 3 1/2 in;

metric sizes are available in 0.05 mm increments in diam-

eters from 1.00 mm to 2.50 mm, in 0.10 mm increments

from 2.50 mm to 10.00 mm, and in 0.50 mm increments

from 10.00 mm to 17.50 mm. Number drill sizes are given

in Appendix 1.1. The included angle at the point of a drill

is 118°. A designer should always choose a hole size that

can be drilled with a standard-size drill, and the shape of the

bottom of a blind hole should be taken to be that left by a

standard drill unless another shape is absolutely necessary.

If many holes of the same size are to be drilled, it may be

worthwhile to alter the drill point to provide the best per-

formance in the material that is being drilled. In very hard

materials the included angle of the point should be increased

to as much as 140°. For soft materials such as plastic or fiber

it should be decreased to about 90°. Many shops maintain a

set of drills with points specially ground for drilling in brass.

The included angle of such a drill is 118°, but the cutting

edge is ground so that its face is parallel to the axis of the

drill in order to prevent the drill from digging in.

A drilled hole can be located to within about 0.3 mm

(0.01 in.) by scribing two intersecting lines and making a

punch mark at the intersection. The indentation made by

the punch holds the drill point in place until the cutting

edges first engage the material to be drilled. With care,

locational accuracy of 0.03 mm (.001 in.) can be achieved

in a milling machine or jig borer. Locational error is pri-

marily a result of the drill’s flexing as it first enters the

material being drilled. This causes the point of the drill to

wander off the center of rotation of the machine driving the

drill; the hole should be started with a center drill (Figure

1.1) that is short and stiff. Once the hole is started, drilling

is completed with the chosen twist drill.

A drill tends to produce a hole that is out-of-round and

oversize by as much as 0.2 mm (.005 in.). Also, a drill

point tends to deviate from a straight line as it moves

through the material being drilled. This run-out can

amount to 0.2 mm (.008 in.) for a 6 mm (1/4 in.) drill

making a 25 mm (1 in.) deep hole; more for a smaller

diameter drill. It is particularly difficult to make a round

hole when drilling material that is so thin that the drill

point breaks out on the under side before the shoulder

Figure 1.1 Tools for making and shaping holes.

TOOLS AND SHOP PROCESSES 3

enters the upper side. Clamping the work to a backup block

of similar material alleviates the problem. When roundness

and diameter tolerances are important, it is good practice

to drill a hole slightly undersize and finish up with the

correct size drill; better yet, the undersized hole can be

accurately sized using a reamer.

Before drilling in a drill press, the location of the hole

should be center-punched and the work should be securely

clamped to the drill-press table. The drill should enter

perpendicular to the work surface. When drilling curved

or canted surfaces, it is best to mill a flat, perpendicular to

the hole axis at the location of the hole.

The speed at which the drill turns is determined by the

maximum allowable surface speed at the outer edge of the bit

as well as the rate at which the drill is fed into the work. The

rate at which a tool cuts is typically specified as meters per

minute (m/min) or surface feet per minute (sfpm). Suggested

tool speeds are given in Table 1.2. A drill (or any cutting

tool) should be cooled and lubricated by flooding with solu-

ble cutting oil, kerosene, or other cutting fluid. Brass or

aluminum can be drilled without cutting oil if necessary.

A drilled hole that must be round and straight to close tol-

erances is drilled slightly undersize and then reamed using a

tool such as is shown in Figure 1.1. Reamers with a round

shank are meant to be grasped in the collet chuck of a mill-

ing machine; the reamer inserted after the drill is removed

from the chuck without moving the work-piece on the bed of

the milling machine. A reamer with a square shank is to be

grasped in a tap handle for use by hand. A hand reamer has a

slight initial taper to facilitate starting the cut. The diameter

tolerance on a reamed hole can be 0.03 mm (.001 in.) or

better. The chamfer (taper) tolerance can be kept to 0.

millimeter per millimeter (or 8 microinch per inch) or better.

Tapered drill and reamer sets are available for preparing the

tapered holes for standard taper pins used to secure one part

to another with great and repeatable precision.

A drilled hole can be threaded with a tap (shown in

Figure 1.1). Cutting threads with a tap is usually carried

out by hand. A tap has a square shank that is clamped in a

tap handle. The tap is inserted in the hole and slowly turned,

cutting as it goes. The tool should be lubricated and should

be backed at least part way out of the hole after each full

turn of cutting in order to clear metal chips from the tool.

Taps are chamfered (tapered) on the end so that the first few

teeth do not cut full depth. This makes for smoother cutting

and better alignment. For more precise tapping the tap can

be placed in a drill press with the work-piece held under-

neath. The drill chuck can be rotated by hand to start the tap

off correctly, parallel to the hole. Some drill presses come

with a foot-operated reversing mechanism so that with the

drill operating at a slow speed the correct action of tap–

reverse-tap can be carried out. The chamfer on a tap extends

for nearly 10 teeth in a taper tap, 3 to 5 teeth on a plug tap,

and 1 to 2 teeth on a bottom tap. The first two are intended

for threading through a hole, the latter for finishing the

threads in a blind hole. The hole to be threaded is drilled

with a tap drill with a diameter specified to allow the tap to

cut threads to about 75% of full depth. Appendix 1.1 gives

tap drill sizes for American National and metric threads.

The head of a bolt can be recessed by enlarging the entra-

nce of the bolt hole with a counterbore (shown in Figure 1.1).

A keyway slot can be added to a drilled hole or a drilled

hole can be made square or hexagonal by shaping the hole

with a broach (Figure 1.1). A broach is a cutting tool with a

series of teeth of the desired shape, each successive cutting

edge slightly larger than the one preceding. The broach can

be driven through the hole by a hand-driven or hydraulic

press. In some broaching machines the tool is pulled

through the work. A broach can, at some expense, be

ground to a nonstandard shape. The expense is probably

only justified if many holes are to be broached.

1.1.3 The Lathe

A lathe (Figure 1.2) is used to produce a surface of revo-

lution such as a cylindrical or conical surface. The work to

Table 1.2 Tool Speeds for High-speed Steel Tools (Speeds can be increased 2 3 with carbide-tipped tools)

Material m/min (sfpm)

Drill Lathe Mill

Aluminum 60 (200) 100 (300) 120 (400) Brass 60 (200) 50 (150) 60 (200) Cast iron 30 (100) 15 (50) 15 (50) Carbon steel 25 (80) 30 (100) 20 (60) Stainless steel 10 (30) 30 (100) 20 (60) Copper 60 (200) 100 (300) 30 (100) Plastics 30 (100) 60 (200) 60 (200)

4 MECHANICAL DESIGN AND FABRICATION