Here I decided how high the centers would be, which among other things (like common sense and self preservation) will determine the maximum radius of wood that can be turned. I wanted the ability to make food plates, which can come from stock that is quite thin (therefore not overly heavy) but has a reasonably large diameter.
Remember the further the drive shaft is from the bed the more leverage it has and the more likely it is to do cheeky twisting, wobbling and other dangerous things. So it is a compromise of size and strength...
Once I had decided that (it was partially determined by the materials i had available), I began by cutting two equal sized pieces from the 8mm thick sheet of metal. I already had two stainless bits which would add a tough outer shell and little bit of rigidity.
Now we need to decide where and how we will fix the front and back faces. I wanted to make them identical front and back panels - I did this by clamping them together and, where possible, drilling through one and into the other a ways so it was easy to resume drilling at the right place.
Again see the pics and their descriptions for more.
Some general advice on drilling... This would have been easier with a drill press (that will have to be a future project though), but you can make do with a decent hand drill - and get quite skilled at using it in the process.. Use plenty of light oil on the drill bits, and go at a slow speed. If you go fast you will harden the steel your trying to drill and dull the drill bit, making it really difficult. Using sharp drill bits helps a lot! (see http://www.instructables.com/id/Sharpen-Your-Drill-Bits/
Always clamp things your drilling, Its easier and safer, and you can concentrate with both hands on making a straight hole.
Consider what size bolt you are going to use in advance, so you can choose the right size bit. You can download tables with the correct corresponding sizes and print it out.
Or, a good rule of thumb is to take the bolt diameter and take away the thread pitch to give the size of drill bit.
e.g. If i want to tap a 6mm thread (because I want to use a 6mm bolt) and if the thread pitch is 1mm, then the drill bit size would be 6mm - 1mm = 5mm drill bit. Rule works just as well with imperial too.