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I am building an archtop guitar. I will be using a dril press to contour the
outside arch on the back and sides. any suggestions on how to control
depth? maybe the use of some depth stopper?

This works well:

Step 1: Drill a 1/4" hole in a piece of wood that will be fastened to your drill press table. It's easier if you don't drill all the way through, but no big deal if you do.

Step 2: Cut a piece of 1/4" dowel long enough to go into/through the hole you drilled and still stick out the top roughly 1" - 1-1/2". Stick the dowel piece in the hole you previously drilled. If the hole was drilled all the way through, glue or epoxy the dowel in; if not, just tap it in until it bottoms out.

Step 3: Fasten the piece of wood to your drill press table, with the dowel positioned directly beneath the drill bit.

Step 4: Set the drill press depth stop so that the distance between the tip of the dowel and the tip of the bit (when fully lowered) is the thickness you want your arched plate to be.

Step 5: Drill away!

I find that a regular drill bit works really well for this. Once I have drilled holes everywhere, I chip out as much of the waste as I can with a chisel. Then I attack the plate with a body grinder until the holes are gone. A regular bit is nice because as you get closer to final thickness, the holes narrow in diameter because the tip of the bit is tapered to a point.

Keep in mind that I am no expert, but I did stay at a Holiday Inn Express last night.

Doh!

The method I described is for carving the inside after the outside is already carved. Sorry, but I misread your original post.

For the outside, use the same method for setting up the drill press/dowel jig. On your plate, draw the equivalent of a topographical map, with whatever increments in height you want. Then use the drill press jig, but this time set the "gap" between the bit and dowell separately for each contour line on topographical map on your plate.

Finally, in your original post you said you wanted to contour the outside of the back & sides; I'm assuming you meant to say back & top.

Let me know if this doesn't make sense, and I'll try to explain it again.Kelby38412.8285069444

Thanks, that clears things up.
So, how does one come up with th depth for the drill bit when contouring
the outside top/back? I have Benedetto's book and I was going to
transfer the measurments from his templates to the plate. Does this
make sense?

That's how I did it --- measuring from the templates.

Another suggestion when carving the outside contours is to start with the thickness of the outer rim established to a uniform thickness. I shoot for 7/32" (to finish later at 3/16") and carry this in about 1/2" from the outer edge all the way around the plate. This gives you something to lay the outer edge of your templates on and also a reference to carve to. It also seems to help to have your overall thickness established and carve the the centerline near to it's shape first. Then you can start carving the various locations around the perimeter using their respective templates to bring the contours to approximate shape. The areas between these template placements indicated in the Benedetto book can then be blended into the template established areas.
I've never used the method of establishing "water line" contours with a drill bit or router but a lot of builders do.
I've since gone to CNC routing the contours to save wear and tear on body parts and then finishing by hand.
Nelson