Mechanic Monday. Tip of the week... axels and alignment.
Anytime that the rear wheel axel nut is loosened both gravity and Murphy will ensure the axel blocks will move away from the adjusters. This will often lead to the rear wheel being out of alignment. A quick and easy way to correct this when it is time to tighten the axel nut is to use a screwdriver or rag between the chain and the sprocket as shown in the photo with the axel nut loose. This will pull the wheel forward and tight against the adjusters allowing the axel nut to be tightened in the proper position. As with anything on your bike always finish up with a visual inspection that you achieved the desired results.
Stay greasy my friends.