This is a photo of my most recent project.

It was mostly built with oak-veneer plywood. The veneer on plywood these days is extremely thin. No, I haven't measured it.

Unfortunately, I managed to sand through the veneer at the corner of my project. It's not in a very prominent location, as in it isn't front and center, but it still is on the top, and I really don't want it to be there! I was not pleased, to say the least.

Replacing the entire table top was not an option.

Flipping it over was also not an option. For one thing, the edging had already been attached, and it was thicker than the plywood. For another, this plywood has a "show" side (with the nice veneer face) and a "B" side (with less-nice veneer.)

Here is a quick demonstration of how I fixed this problem.

You need some sharp chisels, a ruler, a sharp utility knife, and a thin piece of wood. I had some thin oak left over from when I cut out the hardwood edging for this tabletop. It was a bit over 1/16" thick (1.5-2mm).

In order to make the repair as invisible as possible, your wood patch needs to have similar grain and colouration to the plywood. Here I am laying out the wood, looking for the best arrangement. (It's not shown, but I compared two pieces of wood, checking different corners and layouts, before settling on a this corner of that piece.)

I then used the ruler and utility knife (the yellow knife in my right hand) to slice off a narrow wedge of oak. I then rubbed the wedge on some sandpaper to make sure the edges were straight and also to slightly bevel them, such that the bottom of the wood wedge was narrower. This would help with fitting it into the cavity we were going to be excavating.

The wedge of wood -- carefully hidden by my hands so that you can't see it on the camera (not really, that was a mistake) -- is then laid into position and I lightly trace around it with the knife, scoring the plywood.

I then went over those lines several times, each time pressing carefully, so that I can excavate out a section of the plywood that exactly matches the shape of my wedge of oak.

I took my time. Accuracy is more important than speed! I would not want to slip and make a mistake.

I then pulled out the small chisels and used them as well to clean up the hole I was making. I did not try to make it exactly the same thickness as the patch. There is no need for that, as I can later sand or scrape the patch down to match the height of the plywood.

I then could put some wood glue into the cavity, and also onto the back of the wedge of oak, and fit it into place.

The wedge is pretty narrow and delicate, and I don't want to break it, so I used a scrap of wood to distribute the pressure and tapped it into place with my mallet

It was a good fit, but not totally perfect. So I pulled the dust catcher off of my Random Orbit Sander and dumped out some oak sawdust. This sander had been used on this exact project, so the sawdust should be a good match for this wood. I then mixed the sawdust with some wood glue to form a paste and pressed it into any cracks around the edge of the patch.

Dumping some more into place..

A bit of rubbing with my fingers ensured it was pressed into place.

And that is about all there is to it. I let it dry and then lightly sanded it to blend in with the wood around it. (I did not need to sand down the patch, but you might at this stage.) Here are some photos of the finished project after the finish was applied. (I used shellac, followed by 3-4 coats of waterbased polyurethane.)

To my eyes, the patch is virtually invisible. If you know it is there, you can look for it and find it. It helps that this is off in the corner of the desk. In normal everyday use, no one will ever see it.