It's mostly because of bad hinges. Doors sag, they hit each other, or they do a funny flip-flop when you move them, sort of like someone with a hip joint that gets thrown out of whack unless they walk just the right way. The really surprising thing is how many people put up with aggravating cabinet doors.
You may want to cut some type of prop stick that can be wedged between the counter and the bottom of the cabinet to help raise it upward so that it is tight to the ceiling. If the cabinet is recessed back more than two inches from the soffit's edge, you will have to find a wall stud to fasten the cabinet to.
Doors made with properly sealed medium-density fiberboard (MDF) or waterproof MDF are a good choice for protecting against warpage, but they are also less durable than wooden doors. Warping is caused by several factors, including elevated moisture or humidity in the home and insufficient physical support.
When the moisture content in wood is greater than the moisture in the air around it, warping will occur. If an unsealed panel of the solid wood cabinet door starts to twist and warp, it is almost always because of moisture. Either due to water, high humidity, or some nearby dripping water.
This door straightener/stiffener is an adjustable threaded rod for large thin cabinet doors. Ideal for tall and wide door applications in an ever-changing humidity/climate environment and for doors with a heavy finish on one face side, such as laminated or painted doors.
As discussed, solid wood doors have the potential to expand and contract and warp over time. Although this is natural, it can lead to problems if you are hoping to paint your cabinet doors. As the wood changes shape, it may cause paint to crack or chip, especially around the joints and connecting pieces of the door.
Sometimes, if the door is not installed on a level surface, one side of the door could end up higher than the other at the top. Another cause could be that the door hinge side is out of plumb. First, to fix an uneven door, try checking to see if the door is out of plumb by using a level.
Attaching New Hinges
Now you'll want to put the new hinges onto the doorframe (note we're fixing to the frame first and not the door). Before screwing the hinges in you'll want to ensure they sit flush.
One of the main causes of a dropped door is a loose hinge. Luckily, this is really easily solved! Over the years, screws will naturally work themselves loose. You'll probably notice that you've got a dropped door because of loose hinges if the door drags on the floor a little.
All you'll need to do is replace the screws with new ones, but try to find screws that are longer than the original. If you can't replace the screw, try reinforcing the screw hole by glueing small wood splinters (toothpicks are perfect) in the hole and driving the original screw back in.
A thick plywood sub-top fitted over the cabinets before new countertops are laid can help distribute weight evenly over a large area. Alternately, angled iron hardware can be used inside cabinets for a discrete but sturdy reinforcing job.