Re: true a sprocket
I use my "truing stand" which I also use for wheels.
It's a piece of plywood with an oval hole in it, then two drywall screws on each side where the axle sit (they are screwed in at an angle to form a "V")
I then screwed a piece of pine to one side and I can "adjust" it to the rim or the sprocket. I push the pine in until it touches, then turn the wheel to find the high and low spots.