So here's how I make my curved shields:
First make a form out of 2X4s like this one:
Cut the curved pieces out with a band saw if you have one or a jigsaw if you don't. I'll eventually post a link to the template I used for the curve.
In order to make a curved shield you need 2 pieces of 2'X4'X1/4" plywood. Don't get fancy oak plywood or anything because it won't bend like it's supposed to. Just get regular pine 1/4" plywood.
Mark a center line on BOTH sides of your first piece of ply and on the smooth side of the second. Mark the center line down each edge of the ply as well.
Put the smooth side of the first piece of ply facing the form with the rough side up. Use the center line and a reference mark on your form to center the piece:
Then tack the ply to the form with some 1" roofing tacks. DON'T drive them all the way in as you're going to pull them out before you put the next layer of ply down:
Next, tack one side of the ply down on the edge. Drive these tacks all the way in:
Then do the other side. Again, drive the nails all the way in:
And pull out the center tacks so you end up with this:
Now lay out about half of a one-pint bottle of wood glue on the shield in a grid pattern:
Sometimes the glue near the edges will run, so quickly try to spread it all out with a cheap chip brush. Cover the whole surface of the ply:
Put your second sheet of ply on top, smooth side up (so the two rough sides are together). Use the edge marks to line the top sheet up with the bottom sheet and then screw down the center line with 1 1/4" screws:
Screw down one side, being careful to miss the tacks in the first sheet:
Then screw the other side:
Finally, add some screws all around the edges between the first bunch of screws. They'll just go through the two layers of ply:
Then let it sit overnight. After it's dry, unscrew all of the screws and carefully pry the shield blank off of the form with a flathead screwdriver or a small pry bar.
At this point you either need to nip off the ends of the tacks and file them down or design your shield shape so that the edges with the nails in them are cut off.
Remember that your shield can only be as tall as the distance from the ground to your waist. After you have your shape layed out on the blank, use a jigsaw to cut it out. Make sure to cut with your saw on the outside of the curve.