With the help of a homemade nozzle - the so-called grinding “file” for a jigsaw, you can process the edges on wooden workpieces or sheet materials (plywood, OSB, etc.).
You can make such a nozzle from a piece of aluminum T-profile. You will also need a piece of sandpaper with the desired grain size and quick-drying glue.
First of all, it is necessary, using a drill or grinder, to cut off part of the vertical wall of the T-profile, leaving only a low "partition". The edges must be filed to remove burrs.
The main stages of work
At the next stage, the author cuts the shank in the workpiece so that the “file” can be inserted into the jigsaw. To do this, he uses a conventional hacksaw for metal.
After that, glue a piece of sandpaper to the resulting nozzle. Then cut the size of the sandpaper (you can use a scalpel or clerical knife).
Then we insert the homemade nozzle into the jigsaw, and you can start grinding the edges on countertops or other wooden workpieces (including plywood).
Details on how to make a home-made grinding file for a jigsaw can be found in this video.