Making Stained Glass - How do you support a circle glass project?

I have made 3 or 4 small stained glass panels and now may be a bit ambitious! but I want to make a circle panel to be put on top of a small glass top side table. It will be 55cm diameter. I have my design, but I am a bit of a loss how I start to build it up with no frame to support it like you do with a square panel.
I have cut a circle piece of glass as my middle, and then I want to build around that in a mosaic design. How do I keep it still and keep it all together as I make it? Do I cut and fit a few bits at a time and solder as I go ?

Milly's reply:

When you put together a square stained glass panel, you have the wooden batons nailed at right angles onto a board to support your glass for soldering. With a circle pattern it's exactly the same principle, except you have half a circle cut from a piece of robust chipboard or MDF before nailing it onto a board.
The size of the half circle has to correspond with your pattern in exactly the same way that your wooden batons do - ie, you have to take into account the edging material (lead, zinc came) and make allowances for the width of them.
The chipboard/MDF can only be up to half a circle, otherwise making stained glass becomes impossible after a certain point, as you can't fit the glass in!
If you have some very small, fiddly bits of stained glass, you can solder them separately before fitting them into the whole, but you have to be very careful that they're accurately put together before carrying on with your stained glass panel, otherwise chaos ensues...
Hope this explains it for you.