Hey all, Made a little more progress on my brass 3/4" bore mortar. Someone commented on my last post about making trunnion straps. So, I figured I'd share my results. I started by hammering a strip of 1/32" thick, by 5/16" wide brass around a piece of 3/4" round brass that I had. It worked OK. I used a hard leather mallet so it didn't leave any marks. Hardest part was getting the bend where it needed to be. I started off by making the radius-ed portion too long. So, I made a series of attempts at shrinking the piece by hammering the radius-ed part just before the bend on the corner of a piece of steel bar. That proved to be somewhat successful as it did create a new bend before the original one, but creases where the old bends used to be were left behind. With enough patience a guy could make this work and get it hammered back flat. My patience is limited so I had to get smarter. I decided to make a die to form the bend exactly where I wanted it. I grabbed a piece of brass stock I had laying around. I don't know the dimensions, but let's say it's around 1"x 2x2-1/2 or so. Basically I machined a half circle in the block to be a cavity to form the brass strip to. I took a piece of the 3/4" round brass I had and split it in half to make a punch. Now, the center half circle in the brass block has to be off the edge of the block by the thickness of the strip you are using. The radius itself has to be the diameter of your trunnion plus the thickness of the strip you are using. Basically, this is to compensate for the thickness of the material being bent so it has a place to go when you form it around the punch. The hardest part about this process was keeping the strip straight while squeezing the die together. If you don't keep it straight the bends end up angled and look a bit odd. I did the actual forming in my bench vice. I had to hang on to the die, the strip of brass, the punch, and a thick piece of steel laid on top of the punch that formed the flats. An arbor press would make this a whole lot easier if I had one. If I were to make a lot of these I would make a real die with a slot machined in the face about 75% of the thickness of the brass strip and slightly wider. The strip of brass would lay in that slot. It would be like a guide for feeding the material and keeping it straight during the forming process. I would also make the punch more elaborate and add spring loaded pads that would contact the brass strip prior to the punch and would hold it securly in the feed slot while the punch forms the shape. More or less like a real stamping die.
Here's the URL for the pics:
http://pg.photos.yahoo.com/ph/meatpuppeta/album?.dir=7d26re2All of the pics that I have shared thus far are in one folder now including the bore radius tool made from a router bit.Hopefully, this will give you guys some good ideas for your projects.
Aaron
