ENGLISH DECIMALS 

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.

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