Here's some money saving advice:
Since spur gears aren't true all the way around, the gear will not be a perfect circle. What you want to do is set the mesh to have a "tick" of play in the gears. Now spin the spur and pinion so that you can find the depressed side of the spur. Set the mesh to have a tick at that point. Then keep spinning it to make sure it isn't too tight on the other half of the gear.
This will save you money, b/c when most people blame their stripped spur b/c of tight or loose mesh, the mesh could have been right when you first looked at it, but the gear had a low side that was too loose. That low side will break the teeth and ruin the gear.