Machining and CNC Technology1 Section 2 Shop Math Review

Machining and CNC Technology 1

Section 2

Shop Math Review


OverviewLearning Manufacturing Means Math

Nearly every action or decision made by machinists, is based on numbers.

And each is often calculated in some way.

A calculator is as common in the modern tool box as a micrometer!


Section 2 Goals Unit 2-1 Understanding Precision

> Say decimals inches using the language of the shop > Use measurements at one-thousandth of an inch or smaller.> Convert between Metric and Imperial Units. (Review)

Unit 2-2 Self Evaluation> A Pre-Test using typical shop problems. If you can do the problems, skip to the Section 2 Final Review. If not, go to Unit 3 to study the solutions then proceed to the Final Review to see if your memory has been jogged..

Unit 2-3 Detailed Answers> Check Your Baseline Math Skills> Decide if you are warm enough or need a bit of formal math review

Final Review Problems> Did the review do enough to warm up the gray cells?> A second set just a bit harder than the first


Unit 2-1 Working With Precision Numbers In engineering and machining there are

conventions we’ve adopted for working with precision numbers and measurements.

They’re used by all, because we work with and communicate decimal numbers constantly.


Machinist’s Lingo for Decimal Numbers

While we work with inches or millimeters, our base units are much smaller.

For metric units, pronunciation is the same as in the rest of the world: tenths, hundredths and sometimes thousandths of a millimeter.

But when pronouncing decimal inches, our base unit is the thousandth of an inch and we pronounce our numbers based on the thousandth – it has become our adopted base unit.


For Example How would you pronounce this,

12.56 inches?

As odd as it may seem at first, machinists would say either:

“Twelve inches, five hundred sixty thousandths”

or

“Twelve and five-hundred, sixty thousandth inches

Both would be perfectly understood by fellow machinists!


Trade Tip 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.


Shop TalkMachinists might even shorten the

decimal part to

“Five-hundred, sixty thou”


Another ExamplePronounce this decimal number:

0.12 inches

It comes out in machinist lingo

“One-hundred, twenty thousandths”


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 in the regular math world but not in a machine shop.

Not tenths of an inch but tenths of our basic unit, the thousandth of an inch.


For Example Pronounce this number 3.0998 Inch

Three inches, ninety-nine and eight tenths

thousandthsor

Three and ninety-nine thousandths inches

and eight tenths


Trade Tip

Pronounce to the third column, then say

“and X tenths”


Advantages to learning the lingo

You’ll learn to read precision tools like these, much faster and easier.

In industry you’ll sound experienced.

It promotes exact communication between machinists


It’s also important to get a feel for the size of precisionJust how big is a thousandth of an inch?

A millimeter or hundredth of one?

It helps to relate these units to things around us


.047 in.

1.2 mm

CD thickness must be closely controlled so that the read/write beam bounces back perfectly. So how thick do you estimate them to be?

Please, don’t try this on your student CD!


A sheet of paper is Usually .003 inch

Shop shortened to

“Three thou”

Just under .01 mm

“One hundredth millimeter”

or it’s OK to say

“Point zero one millimeters”

Trade Tip

.003 in. can be a useful shim for setups and for measuring!


How about these common items – how thick?

Nickel0.070 to .080 in.1.78 to 2.0 mm

Pen.32 (three-hundred, twenty thou)8 mm


Unit 2-2Math Self Evaluation In Unit 2, you will find two sets of problems

typical of shop work.They will help refresh you math skills, getting ready for lab assignments

They will also help determine if a bit of math review is in order to be successful in the lab and trade.

The best hint is (as always) read the instructions and hints before starting!


Here’s two tips to help:First, if some of the terms are

unfamiliar, look them up in the text. They aren’t part of the test.

Second, be aware of a few built in traps in shop type problems – we call them predictable error points (PEPS)


Remember this small trap, it may come up in the problems!

A Typical PEP

When spaces or divisions occur, be cautious of how many there are!


ConclusionGood Calculating on those problems!

Not to worry, if you haven’t been very successful in math in the past. Shop math is easy to learn because it’s relevant, all the facts are right there on the drawing – which leads us to Section 3 – getting those facts from the drawing.

Documents

Machining and CNC Technology1 Section 2 Shop Math Review