The stumpy arm that connects the cannon to the shoulder has turned out really nicely. It looks quite solid and also passes a few power cables and the like. The entire cannon design is symmetrical and many parts, including the arm, are designed to be able to attach from both sides. While this may limit design choices slightly (everything has to be mirror-able), it's a lot less work than having to build two of these things (even with the CNC cut parts).
I'm still deciding exactly how I'm going to split it up for casting, but I have a feeling it will be four parts: arm, cannon body, barrel assembly and front armour plate. I could mould it with the armour plate already connected to the barrels, but the mould lines would run through the centre of the plate, making them a pain to clean up...
Oh, one other thing I wanted to talk about was the piping. I needed something about 3mm in diameter to use as pipes between the shoulder and cannon body and as details on the top of the cannon body. While I could use styrene tube wrapped in 0.7mm diameter solder for straight sections of ribbed tube, this looked really poor if tight curves are introduced.
I'm a massive fan of the , as they are so easy to work with and will facilitate bends as sharp as 90 degrees while retaining that nice, ribbed profile. Unfortunately, the largest size he does is 2.15mm diameter - a little bit too small for what I needed.
I tried heat bending some styrene rod but could not get a consistent, clean bend without any warping. Similarly using tube reinforced with some solder wire inside.
The solution is very similar to the pewter power cables. Metal rod facilitates sharp bends while retaining the circular profile so I decided that some thicker diameter solder wire would be the way to go. 3mm is 1/8" and that sounded like it would be a common size. I knew I didn't have any but I checked with another engineer friend of mine and he was kind enough to donate a 150mm length to me. It saved me having to buy an entire reel!
The solder behaves absolutely perfectly for this kind of application. To bend it I drilled a 3mm hole in a block of timer, inserted the wire and then just bent it over with my thumb. Because the solder is so soft it can be cut fairly easily using just a sharp hobby knife! It is easy to accidentally mark the solder though, so you have to be careful handling it. I inadvertently made a couple of marks with my fingernail, but not deep enough for me to worry about too much
