Just
a
little
note
about
English
decimals.
In
the
precision
sheet
metal
trade
we
work
with
dimensions
either
in
English
or
Metric
units.
When
working
in
English
units
our
dimensions
are
based
on
a
piece
of
measurement
called
an
inch.
There
are
still
a
lot
of
places
using
fractions
of
an
inch
on
their
blueprints
such
as
1/2"
or
3/4".
When
working
with
these
types
measurements
you
should
convert
them
to
English
Decimals.
This
is
easier
than
it
sounds.
All
you
have
to
do
is
work
the
fraction
like
a
division
problem.
For
example
take
3/4".
On
your
calculator
just
do
3
divided
by
4
which
=
.750.
In
the
precision
sheet
metal
trade
we
usually
work
in
thousandths
of
an
inch
(.001).
Which
means
we
are
just
taking
an
inch
and
dividing
it
into
1000
pieces (1/1000).
This is how we pronounce certain decimals:
.003 is three thousandths
.03 is three hundredths add a zero to the end and it is read as
.030 thirty thousandths (it still is the same value as .03 no matter
how many zero's are added to the end)
.300 is three hundred thousandths
.3 is 3 tenths which is the same value as .300 or .30
.047 is forty seven thousandths
.470 is four hundred seventy thousandths
Get the drift?
Where
that
decimal
is
located
is
very
important.
Some
major
mistakes
have
been
made
by
people
who
have
put
the
decimal
in
the
wrong
place,
me
included.
While
on
this
subject
lets
talk
about
tolerances.
Back
about
fifteen
or
twenty
years
ago
the
usual
blueprint
tolerances
for
sheet
metal
parts
might
have been:
.xxx (three place decimal, thousandths) ±.030 occasionally ±.015
.xx (two place decimal, tenths) ±.060 occasionally ±.030
As
equipment
became
computer
operated,
precision
increased
and
tolerances
could
be
held
a
lot
closer.
Engineers
demanded
higher
quality
and
tighter
tolerances. You may now see:
.xxx ±.005 Yikes!
.xx ±.015 or ±.020
Which
means
you
have
a
lot
less
margin
of
error
in
your
flat
pattern.
You
need
good
press
brake
operators
and
bend
deduction/bend
allowances
that
you
know will work.
ENGLISH DECIMALS
Please Donate if
you find this site
helpful.
Thank-You!
No part of this publication may be reproduced, or transmitted, or stored, in any form or by any means, electronic,
mechanical, photocopying, recording, or otherwise, without the prior written permission of SheetMetalWorkBook.com, Sixth
Edition Reformatted for Internet, ©2012 SheetMetalWorkBook.com