Before you can mill polymer clay, you will need to prepare and bake the clay into blanks. The following is the process I have been using.
Start by conditioning your clay. I do this by kneading small portions, as shown here.
In addition you can use a pasta roller like the one shown below. Once used for polymer clay don't use it for food again.
Combine all the small portions of the conditioned clay into a ball. It is important that they are fully combined without air pockets.
To do this I forcefully roll them into a ball for several minutes.
Next use a roller to flatten the ball just a little.
Place two 6" - 8" long 1/4" dowels next to the clay as shown here.
Place your roller on top of the dowels as shown and flatten the clay. The two dowels will act as a bridge and give you a fairly consistent 1/4" thickness throughout the clay.
Don't worry about too much ends as these wont be used.
Press you cutter into the stock as shown here.
With the cutter still in-place, peel away the excess clay.
Remove the cutter.
Move the clay cutout to a tile as shown here.
As an option you can form and cut the clay directly on the tile.
Place your tiles in the oven. Here I am going to bake four cutouts.
The toaster oven I am using is very accurate. It will maintain temperatures within a couple degrees.
Bake for 1 hour at 280 degrees.