Straight Cuts on a Cheap Plastic Miter Box

I hadn't planned on posting this as an Instructables, but I finally got the results I wanted from a cheap plastic miter box {Meijer grocery store link} after years of not being satisfied with the tool. In the past, most of my miter box work has come out angled in spite of my best efforts. I did some research on the 'net to see what other people have done. Some have built complex jigs; others just gave up. I didn't, and it was worth it! Today, I was able to make square cuts, so I thought I would share the process I used with y'all.

In spite of what the Internet might tell you, DON'T try to do anything without clamping everything in place. I have a portable workbench with swivel pegs {Lowe's link}. To keep the miter box from shifting around, I clamped it between pegs on said workbench. You can clamp it to a table or other flat, stable surface. I then used some F clamps {Lowe's link} to clamp the piece of wood to the far side of the miter box (totally forgetting that the miter box came with pegs I could have used). Why the far side? The miter box saw is designed to cut on the forward/push stroke. With the wood on the far side, you are pushing the wood against the far side wall as you cut, applying pressure to keep the wood straight against that wall. I measured and marked my wood then placed the mark at the far right side of the 90° cut slot gap.

One reason for getting non-square cuts in a cheap miter box is the gap in the slots. The gap is much larger than the width of the saw blade. This allows the blade to move around while sawing. What is needed, then, is a system to keep the blade from moving in the slots. I knew my fingers would always be above the saw's teeth. Therefore, I opted to simply use finger pressure to keep the blade against the right side of the gap.

Many people not familiar with sawing don't realize something. A saw blade is designed to do all the cutting. By applying downward pressure while cutting, you may actually be causing the teeth to grab instead of cut. For this cut, I simply moved the saw blade back and forth, attempting to apply no downward pressure at all. This is particularly important when you are starting the cut; you may need to do a few forward-only cuts to get the saw started. While sawing, apply light sideways pressure to the saw blade using your fingers to keep it pressed against the right side of the miter box gap. This guides the saw to remain straight.

This is the first cut I made using the above process. I actually got a 90° cut! Now it's time to move on to the next part of this project. I am making a drilling jig for placing dowels on 2x2s.