I did not try any conversion tools, I never saw them in any model shop either. But I'm quite happy with the calculator.
Of course, a drill is essential. I bought my first Demel 20 years ago, until it broke. Last year, I bought myself a new Proxxon drill in the new year's sales. For buying all equipment and material, I go "shopping" during the sales period. That's when I buy polystyrene strips and rods for a hole year.
A good ruler is important, too. I use the "machinist ruler" type : flat metal. THat makes it easy to cut plastic with a modeler's knife.
I have a sharp knife installed on a compass to cut perfect plastic circles.
I couldn't find a decent punch and die set in any local hobby shop, so I ended buying two from the internet: one makes round holes, the other hexagonal (to make nuts é bolts).
I found them at Historex :
http://www.historex-agents.demon.co.uk/punch.htmlBefore I start any project, I spend many hours studying pictures, measuring things. Then I work exactly like Gunnie : make a detailed drawing at the exact size. Then start building all individual pieces, one by one... I try to make the biggest parts first. That makes it easier to add smaller parts as the work continues. Preferably, I go for easy parts to start with : straight edges rather than curved, etc... Every piece is thoroughly measured before it is added to the model. Of some pieces, several are needed. I copy those in resin from the one original.
Earlier tonight, I checked on the calipers at the local DIY shop. They come as from € 1.5 (1€ equals about 1US$) for a plastic model to around 12 € for a decent inox steel one. I even discovered a 55 € digital caliper that shows the exact size on a small LCD screen !
I use the inox model. It's ten years old and still as accurate as when it was new.