This miter joint is close to fitting, but it has a slight gap on the inside of the corner. Few things diminish a good wood project like miters with visible gaps. It is a great feeling to make a picture frame or install molding and have tight, clean miters.
Step 1: A quick and easy solution to miter joint gaps
Firmly clamp the members of the joint at the angle needed, in this case a 90 degree corner. Gently run a fine tooth saw down the joint between the two pieces. A back saw or a dovetail saw works perfectly. When finished, slide the members of the joint together and fasten in place with glue or nails.