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 thousandthsGet 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 ±.030As 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 ±.020Which 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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