I got a bandsaw on craigslist recently, and the guide blocks were all whacked out of true. I was having trouble truing them freehand, so I put together this simple jig to true them up fast and easy.
The jig sits flat on a table over a file. The guide block is held in place square to the file and advanced into the file with a depth screw.
Step 1: Cut the Channel
Cut a piece of 2x4 at least 4" long. Choose the file you want to use and trace the outline on the long face of the 2x4. You're going to cut a channel that is a bit wider and a bit deeper than the file is, so that the jig can move freely along the file. (see the pictures)
Step 2: Cut the Guide Block Hole
Measure the width of your guide block and choose a drill bit that has the same diameter measure. Drill a hole in the middle of the channel and square off the corners using a small chisel.
I didn't have a chisel small enough, so I took an old flat head and sharpened it roughly, it did the trick.
Be careful not to take off too much material, check the width often with the gauge block.
Step 3: Add the Depth Screw
Drill a pilot hole in the middle of the guide block hole. Blunt the tip of the screw and drive it into the pilot hole. This screw is used as the depth stop for the guide block.
Step 4: Done! Use It!
Clamp your file down, back the depth screw out, and put the guide block in the slot. Place the jig on top of the file and advance the depth screw until the guide block is just touching the file. Apply pressure to keep the sides of the jig flat to the table, and file away.
Check using a square to make sure that the block is in true. Keep advancing the screw and filing until it is.