Typically my sketches are more “guidelines” than actual blueprints, but lately I’ve had to be much more accurate with my drawings. When I’m working in metal clay, I make my own templates out of paper and tape. (I laminate the paper with tape so that the clay doesn’t get my template too soggy.) Usually I’ll make things symmetrical and get the dimensions perfect in Illustrator. It makes it easy to size up and account for shrinkage depending on what kind of clay I’ll be using.
Right now, my printer is completely broken, which means no printed templates, unless I take a 15 minute drive out to Kinkos. That’s 30 minutes I could be spending sketching! So, I’m doing my templates the old fashioned way. Lots of measuring, multiplying, and then sketching one perfect half.
Then I x-acto out that half, fold it over on the midline, and trace it on the other side! Then cut again, and I have the outside template. From there, I just keep folding and cutting as I build it up in clay, until I have a finished metal piece, and a pile of paper scraps.