When cutting with the jigsaw by hand using it upright, in it’s usual position, we usually find ourselves with the unpleasant “surprise” (after some time using it, it is not so much of a surprise, because we already know what to expect) of making cuts that are far from being straight precise cuts vertically. The top cut, the cut we make on the line we see to guide the jigsaw blade, will look perfect, but underneath the blade is wandering following the softer areas of the wood. That is why if we think about mounting the jigsaw as a table jigsaw we sometimes discard the idea because we think that the same thing will happen to the cuts we would make. But with this simple guide with bearings for the jigsaw blade we can make perfect vertical cuts. It helps to avoid the jigsaw blade wandering.
When mounting the jigsaw under one board, in my case a 14mm thick board, we already saw how, by having the cutting blade fit snugly in the slot of the board, it stayed fairly vertical during the cuts. But even so, a system that keeps the jigsaw blade vertical, and always at 90 degrees to the table top, will allow us to cut the wood without so many worries about the quality of the cut. Although whatever the system is, it must be taken into account that by adding the blade guide system plus the thickness of the board we will be greatly reducing the cutting height that we can perform with our table jigsaw.
This system that I use as a jigsaw guide may not look very pretty, but it is simple to make and to assemble and disassemble from the tabletop. The most difficult part may be finding the necessary bearings and a long cutting blade of sufficient length. I use some bearings that I got from some cheap roller skates. They have the advantage that they are small bearings and do not reduce the cutting length of my table jigsaw too much. And to be able to screw the bearings I simply fit a nylon plug into the inner ring, which I then cut out with the chisel.
With the nylon plug the screw is off-center, but this allows me to slightly adjust the position of the bearing relative to the jigsaw blade. This was a good thing to set the distance between bearings so they don’t press the cutting blade too much between them. Even so, and as I comment in the video, it would have been better to put first only one screw holding the back end of the upper plywood strip. Like that it would be possible to move that plywood strip sideways to adjust the verticality of the cutting blade more easily, and once we were happy with the jigsaw blade position we could screw it definitively.
Keep in mind that this is still a do-it-yourself saw made with a jigsaw tool, so you can’t ask it to do too much work or have the cutting capacity of a band saw or a circular saw.
And just in case you are curious, here are the plans and measurements of the support I use to install the bearings of this guide. It should be noted that the bearings must remain in contact with the blade in the lowest position of the jigsaw blade. The bearings are 23mm in diameter. Larger ones could be used, but would further reduce the cutting height of the table jigsaw.