[Greg Hainsworth]

I operate a small gentleman's farm. Every chain on my equipment has a freewheel sprocket that is controlled with a spring type mechanism to take up slack - a tensioner if you will. You can try to tighten your fab tolerances all you want but you might as well try to shoot an arrow at a target while on horseback blindfolded. It's just the hardest way to get to the result you want.

Look at your chain path and find a location where you can add a sprocket on a bracket that can have use a spring to tighten it. I suggest a spring over a piece of all thread with a nut tightener for this reason - any sudden increase in tension, the spring will give and you won't (shouldn't) shear a crucial piece of your system. A spring is more forgiving.

If a spring isn't feasible, consider mounting one of your freewheel sprockets into a slot instead of a hole and leave room to have some sort of adjustment with all thread to slide that axle in the slot. Small turnbuckles lend themselves nicely to small adjustments but put a nut on each side of the turnbuckle to 'lock it' in place after you make your adjustments. Leave at least a 1/4" play in the chain when you press on it with your thumb (I know that's a really precise test isn't it...) You don't want the chain taught or it will bind and pop. Based upon your question, you already know what is too loose....

Good luck.