Everything was working so well in this DIY jigsaw table that I decided to make a miter sled for 45º cuts to make miter joints. It seemed complicated to get perfect cuts at 45 degrees with a jigsaw table, but the fact that the cuts came out as deviated as they did caught my attention and made me think that it was not a problem of the miter sled I made, but that it could be a problem of the jigsaw itself.
The base of the miter sled for this jigsaw table is the same as the one I made for the crosscut sled for 90º cuts. The only thing that changes now is the fence that goes on of the base. Now it is a square triangle with a perfect 90 degree angle facing the cutting blade. And each side of the square triangle make a 45 degree angle with the cutting direction of the blade. Being very precise when putting it in place is not easy, so this time instead of a wood strip I put a right triangle of plywood in a way that the perfect right angle is facing the cutting blade.
You can watch in the video how I placed the square triangle in its position, with its two sides at 45º to the cutting direction of the jigsaw blade. This way, for each miter joint, I can make one cut with one workpiece against one side of the triangle and the other miter cut with the other workpiece against the other side of the triangle. The advantage of this is that if the triangle is slightly offset, the offset I have by cutting on one side is compensated in the opposite direction by cutting the other side of the miter joint on the other side of the triangle. The result should be a miter joint making a perfect 90º angle. The reality is that even if we get the perfect 90 degree angle, one of the cut surfaces of the joint will be larger than the other and it will be noticeable, although not much if the deviation is small.
So far all the theory seems simple, but as I said at the beginning of this post I found that the angle that results of the joint of the two cut pieces was very deviated from 90º, which led me to think that there was something wrong, probably in the saw. I tried again cutting a wood strip with the crosscut sled that I made a few days before and that then worked perfectly, but now I had a slight deviation in the cut as well.
Looking for what could be wrong I noticed that the jigsaw blade does not fit very tightly into the clamp mechanism of the jigsaw, and it is easy to divert the front of the blade to one side and to the other, thus ruining the blade alignment work I had done. As seen in the upper picture, I have another jigsaw with another different blade clamp system that seems more reliable, as after manipulating it for a while I find it much more difficult to divert the blade sideways. I think I will mount this jigsaw under the board as a jigsaw table and see if it gives a better result. If not, the best option is to make a sled to make miter cuts with the table saw.
According to the comments on the YouTube video, this problem of the blade divert is quite common in some DIY jigsaws, so they recommend me to buy a higher quality one. However, even if the jigsaw has that problem, I believe that having the saw mounted with the guide with bearings for perfect vertical cuts at 90 degrees can be very useful, since cutting by hand, without using a sled, the cuts come out quite well. Perhaps the cuts are a little slower to make, since you have to compensate the cut continuously, but with the help of a disc sander and simple guides for sanding at 90º and 45º we can get a perfect result. And even if you don’t have a disc sander, using a good enough quality jigsaw cutting blade, and some light sanding to remove wood burrs, the cuts are good enough for many DIY projects.