In the early days of CAD most companies had pen plotters and the pens for the plotters where generally black. There were other colours available for the plotter but just like hand drawings the use of multiple colours wasn’t really a sensible option.
Back in the 90’s the company I worked for had a Dyeline printer which would reproduce drawings up to A0 size. The original film drawing was laid over a yellow diazo sheet of paper. Both pieces were then fed in some rollers which took them into the exposure part of the printer.
They passed in front of an ultraviolet tube where the ultraviolet light penetrated the original and neutralized the light sensitive diazo sheet. This then left a perfect image of the original on the diazo sheet, albeit a faint yellow copy.
The film original is then taken away and the diazo sheet is fed into another set of rollers for development. A chemical reaction in the development chamber results in the unexposed yellow lines changing into dark visible colours and leaving an accurate copy of the original drawing.
This was a very time consuming process that sometimes meant spending days in the print room on large jobs that were required for quotation. Because we still plotted drawings on film if multiple copies were required it would still be cheaper to use the Dyeline printer than to plot more drawings out, wasting ink and film.
When we create drawings in CAD we use different colours so it makes life easier to see what is going on. With complex assemblies having different colours on the screen is incredibly helpful.
When I draw in AutoCAD these are the colours I tend to use:
Outline and text: black
Dimensions: green
Dimension text: red
Hidden detail: magenta
Centreline: cyan
So when our pen plotter got replaced by an inkjet colour printer you might assume that we would start printing out drawings in colour to match what is on the screen. However as stated in a previous blog, whilst printing in colour can make general manufacturing drawings a bit clearer, if the line weight has been setup correctly then I don’t think it is necessary.
It is also worth mentioning that the larger inkjet printers, just like small home printers have 4 cartridges: cyan, magenta, yellow and black. As these cartridges are not cheap it would get very expensive if a company committed to printing in colour only.
So is there ever a need to print out in colour?
For general manufacturing drawings I would say no, but for architectural and infrastructure drawings I believe it is highly beneficial. The use of colour when used correctly can be the clearest way to show information on a drawing.
I feel with colours that less is more and there is nothing worse than seeing a drawing where an operator has gone a tad crazed with colours. Just because there are hundreds to choose from it really doesn’t mean you need to use them all. It can make a drawing very messy and confusing.
I have produced factory and office layouts and by printing them out in colour the drawing is so much clearer to understand, especially complex ones.
Many companies are now happy to receive PDF files instead of printed out drawings. This has prompted me to change my AutoCAD background to white even though black is easier on the eye. This ensures I know what the drawing will look like if it was to be exported in colour and helps avoid colours that won’t show up, like yellow. The goal is to always make sure that drawings will look clear and easy to understand whether printed in monochrome or colour.
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