How I Made My Coat of Plates
I purchased a side of 5.5 ounce leather from Brettun's Leather Village for $50, including shipping. It was 24.25 square feet of beautfil black vegetable tanned leather. This was more than enough to fit me, and I'm the size of an NFL lineman I would heartily recommend Brettun's over any other leather distributor.
I purchased 2lbs of round head rivets (3/8" length, 3/16" diameter) from R.J. Leahy for $3.50 per pound + shipping. I also picked up a box of 100 washers from Home Depot. You're going to need the #10 washers. #8 is a bit too small and they don't make #9's!
I used this pattern from the Armour Archive (I didn't use the complicated looking pattern at the bottom, but the one right above it). Its pretty comprehensive and unless you're a guy my size, you can easily use those dimensions for your plates. I drew up the patterns in cardboard paper first (you can use folders) and then traced them to the steel. If you don't have any, go out and get yourself a crapload of Sharpies - you'll need them and they tend to disappear into thin air when you need them most
I used 16 gauge mild steel which I picked up from a fabrication shop. A 4'x8' sheet only cost $40, although I understand this is somewhat high. You will only need, at most, a 4'x4' sheet. I cut my pieces based on the pattern measurements provided in my link above. Make sure you take care to drill/punch holes in your torso plates just like on the link above as this is important to keeping your ability to flex and move. I used an electric shear to cut my plates, but since that has burned out, I'm using aviation snips to cut through plate. Actually, I'm using them to cut 16 ga stainless for some finger gauntlets I'm working on.
Actually making the coat of plates is really easy since there is little skill involved. At most, the most skilled acts you will do in this project are taking correct measurements and bending the plates so they uniformly fit your body. Peening the rivets down is easy.
If you don't have a rivet set already, then here's how to make one. If you have a piece of barstock around 1/2" or larger, clamp it in your vice so it is standing vertical and drill an indentation the size of your rivet head, which I believe is 5/16", although I can't remember for sure. You only need to drill it until the head of your round head rivet sits completely in the indentation you are drilling. If you don't have the barstock or would like an alternative solution, go down to any place where they sell fishing supplies and pick up a few 2lb lead fishing weights. These will become quite useful as you do more and more armour work. You don't have to drill holes in the lead, you can just set the rivet head on the lead and peen your rivet and a properly sized indentation will be made. Try not to handle the lead too much, and wash your hands after you touch it, as it is toxic. You can just take a ball pein hammer and smash the ball so it has a flat top and bottom, which makes setting rivets easier.
After measuring myself and cutting out my leather coat, I flipped the leather upside down so that the shiny black part was on the ground and the dull, lighter side was facing me. Then I arranged all the plates where they are supposed to go and got a good idea on how it was going to look.
The next step is drilling the holes in your leather coat. Start with the bottom-most plate on your stomach and place it so the top of the plate is level to where your bellybutton would be. To help me find where my bellybutton would be on the leather coat, I put it on and marked a spot where my bellybutton is, then I flipped the coat over and marked that same spot (approximately) on the lighter side of the leather. Then, as I have the steel laid on the leather, I marked my holes by putting the Sharpie through the holes on the steel and onto the leather. Sounds elementary, but I want to cover every detail possible Then drill the holes you marked with a 3/16" bit.
Then move to your next plate up on the torso. Arrange it so that the bottom of that plate comes just below where the rivets are on the plate beneath it so that the plates slightly overlap. Then mark and drill your holes and move onto the next piece. The side pieces should be close to the torso pieces just like in the pattern, i.e., there is little, if any, gap between the torso plates and the side plates.
Once you have all your holes marked and drilled, you can then start forming your plates. Since you're using 16ga mild steel, you can pretty much bend the steel by hand over your thigh or something. If you have actual forming tools like big (in diameter) sections of pipe and mallets, you can form the plates that way. I bent the torso plates over my thigh with my hands and didn't curve the side plates at all, although you can certainly do that if you want to. Curving the side plates give them more strength and help fit your body more. You can do this a number of ways. First, you can take a section of pipe roughly 1.5" or 2" in diameter and clamp it in your vice horizontally, so the top of the teeth of your vice are holding the middle of the pipe. If you can find barstock that large, by all means grab it up. You don't want to tighten the vice too much or else you'll squish the pipe. Then grab your plate by the end with either your hand (gloved, of course) or some vice grips with the teeth ground off and hold it over the pipe section. Then take a large wooden or rawhide mallet and hit the plate so that it forms a nice curve. You only need to make a gentle curve that will conform to your side. Another way of forming and strengthening the side plates is to dish them using a non marring hammer (I used a 1 pound rawhide mallet from Orchard Supply) into a dish that is approximately 3" in diameter and 1/2" deep, possibly even 1/4" deep depending on your body shape and personal preference. The deeper dish will obviously give you a more pronounced dish while the shallower bowl will leave you with a more subtle dish.
Once all the plates are formed, I start riveting them to my leather. This is by far the most time consuming part of the job. My coat of plates using this pattern took almost exactly 6 hours to peen all the rivets down, and I didn't stop but once. Put a washer on your rivet (always use washers on rivets that are being attached to leather so they don't pull out) and slide it through the hole in the leather and plates, so that the head of the rivet is visible from the outside of the leather. I understand that metal washers will eventually erode the leather away when mixed with moisture, but I've talked to people who have done this and said their coat of plates haven't had problems in upwards of 8-9 years. Then take your rivet set (or lead weight) and place the rivet head in it. This part is tricky at first, but you'll get it. Once you have your rivet head in and the shaft of the rivet is sticking up through the leather and steel, take a ball peen hammer and strike the rivet shaft with the flat face part a couple of times to make it fatten up and fill in the hole more. Then turn the hammer over and strike the edge of the shank of the rivet so it mushrooms out. Continue doing this until you have succesfully smashed the rivet head tightly against the steel. Then continue doing this until you're done, which like I said above, is a long time.
As time goes by and you fight in your coat of plates, you are bound to sweat meaning that your mild steel will eventually rust. You can prevent this by painting the plates on the side that will be towards you so they don't rust or mess up your clothing. The reason I wouldn't suggest painting before riveting the plates on is because after the paint has dried and you are riveting the plate to your leather, missing the rivet and striking the steel will cause the paint to chip/flake and the time you spent rust proofing your steel will be lost and you'll have to clean up paint flakes.
The next step is adding shoulder protection. You can choose to use the design of the original Wisby coat of plates (the triangular shoulder piece) or you can use spaulders, the pattern for which are here.
For buckles and straps, I used some scraps of my black 5.5 ounce leather from my coat of plates and some 1" buckles that I purchased from Siegel of California. They were part of a bargain bin and I got a good deal on them, but their customer service frequently...well..sucks. I've also ordered some 10ounce leather from them which I used as backing for my splinted armour.
I put one buckle connecting the two sides behind my back (straps going horizontally), and two buckles holding up the sides behind my back (straps going vertically).
Best of luck and feel free to email me with any questions/critiques/comments at firstname.lastname@example.org