Using engineering scales
Most CAD systems allow the drafter to draw at whatever scale he or she feels like. However, if fabrication shops are going to be using your drawings you will help them far more by drawing views to commonly accepted engineering and architectural scales.
Many shops like to keep drawings to a consistent scale so fabricators get used to knowing how drawings are laid out. This is just as important in plant layout and architectural drawings where 1/8"=1'-0" and 1/4"=1'-0" are standards for construction and building permit work. In machine design 3"=1'-0" and 1-1/2"=1'-0" are very commonly used in weldments and small assemblies. Details can be full size or half size.
If estimators are going to be taking off material requirements from your drawings they will also need to have the drawings made to scale so they can calculate the number of panels required, steels sheets, rod or bar, whatever it might be.
Drawing to scale is also important since the CAD system can make scale templates more accurately than ever before. Drawings can be plotted at full scale and parts can be checked against them simply by placing them on the drawing. Paper plots can be glued to wooden forms and templates can be sawn to shape with minimal layout time.
The following table shows typical engineering scales and useful data to help set up your sheet layout.
There is also a small engineering scales power point presentation with sound that I put together about this subject. It's worth a listen if you are just learning the process of setting up drawings to scale.
You can use this chart in many different ways. Most often you would be starting off with an autocad file that was drawn full size in model space and now needs to have a drawing border to a specific drawing scale placed around it.
Calculated Industires has this neat little gadget for scaling off large printed drawings. This is particularly useful for estimators who must quickly find linear feet of cladding or pipe or any number of items from a large drawing set. The device works by first setting the scale then rolling a small wheel along the length you want to measure and reading the distance.
How to Scale a drawing to make sure it is accurate
Simply draw your drawing border actual size and scale it up using the reciprocal numbers until your object fits nicely within the drawing border. Under drawing scale in the title block, label the scale from the chart whose reciprocal created the best fitting border
Also if you have a drawing border that is 3/4"=1'-0" and you want to make it 1/2"=1'-0" look up the reciprocals for both scales. Since you are making your drawing border smaller in this case you need to divide 16/24 = .6666667. Scale the original border down by this amount and your scale is changed.
The Ratio and Decimal numbers can be helpful if you are working in paper space and need to know what the scale factors are for window resizing in order to create the proper scale.