When we cut freehand with our jigsaw, we usually have a disguising surprise (well, after sometime using the jigsaw, it is not a surprise anymore): the cuts are not as straight and as vertical as expected. If we draw a cutting line, we may think we are making a perfect cut while we follow that line, but the surprise comes when we turn the workpiece. The problem is (this is what I think) that the jigsaw blade always tries to follow the soft wood (when we have a soft grain and a hard grain in the wood we cut), so the tip of the blade bends trying to follow the softwood. So the cut in the back of the workpiece is neither straight nor vertical. And for that reason we may think that, if we make a jigsaw table, we will have the same problem. But, we’ll see how to make a simple blade guide, to keep the blade vertical while we cut, so we can make perfect vertical cuts.
Due to the way I mount the jigsaw under the plywood board, to make a jigsaw table, because the blade is tight in the slot in the plywood board, it keeps quite vertical when cutting. But even so, it is better to make a guide to make sure the blade will always be vertical so we can make perfectly vertical cuts. That way we don’t need to worry about that when we cut. But it doesn’t matter the kind of guide we make, we must take into account that the board plus the guide will reduce the maximum hide of cut of the blade we use in the jigsaw table.
Maybe the blade guide I make to keep the jigsaw blade vertical is not very nice, but it is very easy to make. And it is also easy to install and uninstall in the jigsaw table. The most difficult part is to find the small bearings and a long blade. I got the small bearings from a kind of rollers. I use these bearings because they are small in diameter, so they won’t reduce the height of cut more than needed.
To be able to screw the bearings to the plywood I simply insert a nylon wall plug in the holes in the bearings. And I cut them to the same thick. Using those nylon wall plugs, the screws are not well centre in the hole, but that is helpful to adjust the position of the bearings to each side of the blade. Even so, as you can watch in the video, it would be better to use just one screw to screw the plywood that holds the bearings. That way it would be easier to adjust the bearings position in this blade guide. And then I would use more screws to hold that piece of plywood.
You must realise this is not more than a little DIY electric tool. So, you cannot ask it as much as if it were a band saw. It will never have that capacity.
There you have the plans of the guide I have just made. If you make one you should adapt it to your jigsaw table and to the blade you will use. The most important thing is, that you must make sure, that the jigsaw blade is yet between the bearings when it is in the lowest position. The bearings I use are 23mm in diameter. I could use bigger ones, but they would reduce the height of cut.