Here's an example of a manufactured plate along side of a thin metal, home-made plate. Essentially the plates either split a bait into two sides , as in the home-made plate, or the manufactured plate allows only one side of a mold to be shot. The resultant baits, when shot with the finish plastic have a very uniform, straight line of color separation. In the case of hand-made plate you have two sides of the plastic to work with IF the un-vented side fills complete enough to give you the parts you need.
You'll note that the thin plate shown is for a small fry mold, the 1 3/4" mold specifically. The mold shown along side the thin plate is the 3 1/2" super fry and it's companion lamination plate. On the large fry, the plate as it comes from the plant shoots the top, or back section, of the baits. I've modified it by drilling the extra holes in the plate itself and in the lower half of the mold so I can use the factory plate to shoot the bottom half of the mold only which allows me to have more manipulation of the belly section, such as shooting tails or hand-pouring the belly 3/4 full, adding the plate to shoot the line or middle color, and then shoot in the top color.
There are a lot of handy materials for plate making that will not require altering the molds as long as they are THIN. The metal I used in the small fry plate is punch metal that I purchase at a local Hobby Lobby. Michael's Craft Stores also carried this and other similar thin metals. This material is tin and I prefer it over copper or brass simply because its cheaper. I use a simple kitchen scissors to do major cutting but will clean up those cut-outs with a Dremel. The holes are located, marked and drilled first after cutting the sheet to size. You'll want the holes to align the cut-out for the injection port and you'll want to have the plate in place and set the injector in the port to make certain none of the metal sheet keeps the nozzle from seating completely. For as much work as it sounds like, I have not spent more than ten minutes making a plate for any mold.
I'll also note that very few of my molds have not been modified in one way or another, mostly in the venting department so I can achieve full halves when using thin plates.
Bass Buster brings up the hand pouring convenience. I prefer hand pouring if I am doing just a few baits. Hand pouring also allows the baits to come out in the end a whole lot more natural looking because there are no stark, sharp lines....the separate colors will sort of fade into one another as in a natural fish or minnow. I advocate the plates for convenience and for speed along with helping people to make very nice looking baits, but I also advocate learning how to hand pour partial cavities and my biggest tool for that is a spoon where control of the plastic is easily mastered. When doing frog bellies I pour right out of the cup, but other-wise I use a spoon.
