When I first started making my own couplers, I was having a pattern made by Shapeways in brass. I was sending these to a foundry, where it was duplicated in the investment casting process. After a while, when I looked at how much I was ordering from the foundry, I realized it would be cheaper for me to do the wax injecting myself. I have several years experience in resin casting, so the transition was pretty smooth. I bought my own wax injector, a couple different flavors of wax, and started experimenting with platinum based RTV (all the Tin-cure RTVs I had any experience with were too soft). It didn't take long before I was successful.
My first iteration of this coupler included the centersill as a cast piece:
After running a few, I could see it wasn't cost effective. I was looking at $10-$12 for each centersill. I also intended to attach the bottom plate with screws. I was not thrilled with the idea of drilling and tapping all those tiny holes, but I couldn't think of anything better. I also did not have a good answer for replicating the draft gear mechanism.
Then the light bulb came on: photoetch. It would require soldering, but I figured I could silver solder the front & rear draft lugs, and the striker plate. Then I could assemble the whole thing and solder the bottom plate on with a lower temp (silver-bearing) solder. It worked acceptably, but I can see after making one up, I need to tweak the fit of some things. Its hard to calculate exactly how the photoetched parts will bend, and a few thousands of an inch makes a difference. And the price came way down - like $2 each.
In my next revision, the striker plate and the front draft lugs will be once piece. They are designed to lock into the centersill when its folded, so no need for a clamping mechanism for soldering. I'm also going to try using .032" rivets to hold the bottom plate in place for soldering. Will post more photos as I progress.