Lesson 1
Shop Safety
Shop Math
Decimal inch system
Rules
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Shop Safety

YOU are responsible for your own
safety and proper machine
operation.

Use common sense….if you don’t think it is
safe don’t do it.
Ask questions.
Note location of all emergency stops in the
shop
Note locations of fire extinguishers and
pull stations



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Safety Procedures
Always wear eye protection
 Wear short sleeve shirts. Loose
sleeves can catch on rotating work
and quickly pull your hand or arm
into machine.
 Wear shoes/boots - preferably steel
toe work shoes/boots.
 Never wear gloves
 Remove wrist watches, necklaces,
chains, rings and other jewelry.
 Tie back long hair so it can't get
caught in the rotating work.

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Learning Machining Means Math

Nearly every action
or decision made by
machinists, is based
on numbers.

And each is often
calculated in some
way.
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Working With Precision Numbers

In machining there are conventions we’ve
adopted for working with precision
numbers and measurements.

These conventions are very commonly
used because we work with and
communicate decimal numbers
constantly.
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Machinist’s Lingo for Decimal Numbers
Base units in the machining world are a lot
smaller than inches or millimeters.
 For metric units
 Pronunciation is: tenths, hundredths and
sometimes thousandths of a millimeter.
Note: we will not be using the metric system in the
shop
 For decimal inches
 Our base unit is the thousandth of an inch and we
pronounce our numbers based on the thousandth

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For Example

How would you pronounce this,
12.56 inches?
“Twelve inches, five hundred sixty thousandths”
Add zeros when the number doesn’t go to the third
column
12.560

Mentally adding zeros helps to say the number to the
third decimal place – the thousandth column.
“Twelve inches, five hundred and sixty thou”
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Another Example
 Pronounce
this decimal number:
0.12 inches
In the machine shop you would
pronounce this:
0.120
“One-hundred, twenty thou”
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Dividing Thousandths

For some extra-precise work, thousandths aren’t
fine enough.

For these situations we divide each thousandth
into ten smaller parts – called “Tenths” in
machinist lingo, 0.0001 Inch that’s our tenth.

0.0001 is called one ten-thousandth.
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It’s also important to get a feel
for the size of precision
 Just
how big is a thousandth of an inch?
 Take 1 inch and divide it by a thousand.
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CD thickness must be closely
controlled so that the read/write beam
bounces back perfectly. So how thick
do you estimate them to be?

.047 in.
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How about these common
items – how thick?

Nickel
0.070 to .080 in.

Pen
.320 (three-hundred, twenty
thou)
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A sheet of paper is

Usually .003 inch
Shop shortened to
“Three thou”
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Rules

One of the most practical and common
measuring tools available for machining
and rough inspection of parts is the rule.

A steel rule is a linear measuring instrument
that has engraved lines referred to as
graduations.
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Different types of Rules
 Decimal
 Fractional
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Care of rules

Rules are precision tools; only those that
are properly cared for will provide the kind
of service they are designed to give.

Rules should be kept separate from
hammers, wrenches, files and other hand
tools to protect them from damage

Rules should not be used as a screwdriver
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Reading rules -Parallax Error
 Parallax
error occurs when the observer
making the measurement is not in line
with the workpiece and the rule.
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Measuring round objects


Measuring round object can be difficult because
your measurement will change based on where
on the circle you are holding the rule.
What you want to do is slightly pivot the rule on a
reference point a take the largest measurement.
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Reading fractional rules
Fractional rules come in 1/8, 1/16, 1/32
and 1/64 gradations.
 The length of the gradation lines vary,
with the 1” being the longest, the ½ inch
line being the next in length, and the ¼,
1/8, and 1/16 inch lines each being
consecutively shorter.

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Fractional Rule Gradations
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Reading a fractional Rule
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Reading a fractional Rule
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Reading a fractional Rule
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Reading a fractional Rule
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Reading decimal Rules
 Decimal rules come in two gradations 1/50 and 1/100
 On the 1/50 scale each inch is broken into 50 equal
parts with each part equaling 1/50 of an inch or 0.020
(twenty thou)
 On the 1/100 scale each inch is broken down in 100
equal parts with each part equaling 1/100 of an inch or
0.010 (ten thou)
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Reading decimal Rules
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Machining and CNC Technology
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