I debuted my WS cosplay on the weekend so I thought I would share my arm build in case it's helpful!
As I mentioned earlier in the thread, I built a foam muscle suit (just the arms) since being a woman and not exactly that buff I needed to fake it. The muscles I made from the foam suit are what I used to shape the Worbla cyber arm. Much like the stunt arm used for filming I made it in two parts (plus the glove with fingers, which I've also posted earlier in this thread). I used some silver spandex for the elbow and shoulder. I used body filler to even out the surface (you will invariably get some crinkles with the Worbla), then primed, and then gave several coats of Spray Putty. I was originally going to etch in the details, but I found that there was a chance of the putty/primer layers might lift off - I had some cracking and lifting in areas, so I went over with a layer of PVA to be safe and fill in the fine hairline cracks. It was my first time using the Putty and filler, so I may have done something wrong. Instead we sprayed a coat of black, masked off the details with painters tape and then sprayed with the chrome paint. It was the night before the con so it was the best solution for the time frame, but I think it worked pretty well.
The arm pieces are not actually attached, they slip over my muscle suit and just stay on. I do need to attach a strap for the top piece at the shoulder, as it does slip down a little, and I don't like how the shoulder lifts up. But again, I was running out of time, so I'll add that before I next wear it out. Pics below. Any question fire away, but I hope it's useful for anyone looking at cosplaying dear Bucky
Oh, and I also custom built a screen accurate harness, so I can post that process too if anyone is interested!