Well I tried - I swear I did! One of my friends told me that he often replaced entire cabinet corners and edges with rock hard water putty. He obviously had better luck than I did because my corners just wouldn't stay put. They really looked nice for a while but just before priming they fell off!
I had to revert back to the tried and true method of replacing the cabinet corners with new wood. I think this is a better solution than using putty but I wanted an easier way out. This really isn't so hard though.
The first thing we need to do is take a look at our crappy corner. Here's an awful site...
The next step is to figure out how large our new piece should be and cut it. Don't try to replace a small piece of wood. You'll have more problems trying to keep it attached than you would with a larger piece. Take advantage of this opportunity to fix broken edges also! Make the new piece nice and big.
I started by getting the scrapped monitor shelf and squaring the ends on a table saw. Then I took what was left and held it up to the cabinet. I made a decision about the length and height of my new piece and put some pencil marks on it.
Back on the table saw I cut a new piece - nice and square. That's square as in straight 90 degree angles. The replacement piece is actually rectangular.
After cutting my replacement piece I laid it on the cabinet side and traced around it with a pencil. Then I set my router on top of the cabinet with the bit on the edge of the pencil line. I brought a piece of scrap wood up against the edge of the router base plate and fastened it to the cabinet with a c-clamp. I moved the router further down the pencil line and made sure that my scrap wood was still placed correctly. The router bit should still be on the pencil line. I clamped the scrap wood on the other end and now had a router guide.
The same technique was used for positioning another router guide (piece of scrap wood) for the second pencil line. Now that I had defined boundaries for my router it was time to cut.
Using the guides, I made three passes across the cabinet side at different depths. This allowed me to cut the piece out entirely without burning up the router bit. As you can see in the photo, I was left with a nice square opening - exactly the size of my new replacement piece.
Removing the old corner from the cabinet is a little more involved. Cabinet sides are often fastened to bottoms, fronts and shelves by using dado's. The sides will have dado's and the shelves, fronts, etc. will have rabbets which fit into them. The old corner was fastened to the front and bottom with a dado which had to be brought level with the thickness of my replacement piece (3/4").
Using the router, I made several free-hand passes over the corner, just above the cabinet bottom and front. This removed the rabbet from the bottom and front pieces and made them 3/4" below the cabinet side. If you're not sure what I'm talking about, pound the corner piece off with a hammer and look underneath. Then pound the corner back on and go over it with a router. The photo below shows the cabinet front and bottom exposed. These two pieces used to have a rabbet on them.
After removing the corner and any left over rabbets, sand the cabinet bottom and front pieces to make them flush. Place your new corner piece on top and pre-drill several screw holes through the piece and into the sides/front. Counter sink your pre-drilled holes and test-fit your screws by screwing them in. The replacement piece should either fit flush with the existing cabinet side or be 1/32 or less above it. It can always be sanded down later.
Unscrew your new corner piece and apply a liberal coat of Elmer's wood glue on all connecting edges. Make sure you coat the cabinet side, front, bottom and replacement corner edges. Set the new piece in place and screw it down.
You're corner should look something like the one above. The trick in getting a tight fit is to use the pre-cut replacement corner to mark your lines. Then use a router to cut along the lines with a dado bit.
Let the corner dry overnight and cover the screw holes and exposed butt joint (where the new corner meets the old cabinet side) with wood putty. The butt joint is very tight after the glue has set up. If you're really worried about the new corner falling out then you can use a lap joint to connect it to the cabinet side. You could also leave the rabbet's on the cabinet front/bottom and cut dado's into your replacement corner.
I pulled very hard on my new corner to make sure it was secure. I'm confident that it's just as strong as the entire cabinet side.
After a final hole patching and sanding, the transition between the cabinet side and the new corner should be seamless. With primer and paint, the repair will be completely invisible.
Because I replace a front corner on the cabinet, I had to re-cut the t-molding dado. I could have clamped a bunch of wood around the edges of the cabinet and used a router but I decided to do it freehand with a Dremel tool. This just seemed a lot easier to me.
As you can see in the photo above, I used a Dremel cutoff/sanding disk. It looks like it's made of fiberglass but is rough like sandpaper. I cut the dado on both sides of the cabinet without a fence or guide. (I replaced 2 front corners) The cutting was quite easy and my dado ended up straight and clean.
Second Chance Arcade