don't tell me you've noticed the position of the blade from the photo!
had to sharpen it a couple of times while trimming the edges of the robot this week - missed one screw and shaved its head, the blade didn't like it at all! It's really good on hdpe though when sharp.
Btw we use oil stones for sharpening over here, water stone could be something similar but I've never used one.
re. welding I'm happy with the result, makes it easier to attach parts where its difficult to use fasteners, wish I had tried this a bit earlier, it would have spared me a lot of sweat and swearing!