Joining together two pieces of wood at a 45º angle or miter cut doesn’t seem to be a very difficult task. And if we have a miter jig, what can go wrong?. Well, almost everything. This is because you need to be very precise when you measure and when you cut or you won´t get a nice join. That is why I decided to make this circular saw miter jig.
Video with subtitles in English:
The first thing we must take in account is that the boards we want to join together must be the same thick and the same width. It is not only a question of buying them with the same dimensions or in the same shop. Sometimes, even each end of the same board have slightly different dimensions. We must cut the pieces we need, two or three centimetres longer than needed, and put them side by side to check if they are exactly the same thick and width. This won´t affect the join itself, but after the glue dries we´ll see that in the inside corners, and in the front or the back of the joint, some of the boards aren´t flush with the other boards. You probably know that this means a lot of time sanding to level the surface. So, before we miter cut using a miter jig, a miter saw or a miter box, it is better to to use a planer to make sure all the boards are the same dimensions.
Next we need to make the most perfect miter cuts we can. We can use a miter saw, but remember that we must perfectly adjust it so that the cutting angles are perfect. Another option is to make a homemade circular saw miter cut jig like the one I show you in this post.
To make this circular saw miter jig we need, first, to make a homemade circular saw cross cut jig that we will modify to make 45º cuts. In the video I show you how to modify it. You will need a square with perfect 45º and 90º angles. The cheapest and trustworthy square I could find is one of these green Faber-Castle squares. I will keep it in my shop because it is more precise than my cheap yellow square.
I can´t afford a planer so I made a homemade planer with my electric hand jointer.
And now something we sometimes don´t take in account, but that can result in ugly joints, even if we have the most perfect 45 degrees cuts. If we want to make a square or rectangular frame, the pieces of the frame that are one in front of the other must be exactly the same length. It is not a question of having a very precise measurement tape, good eye or be very skilled. We need to measure one and put it in the jig. Then we clamp a stop and make the miter cut. Now we put the next piece in the jig with the help of the stop we clamped before. You can see in the video all the procedure. Now we are sure both pieces are exactly the same length.
Beware if you make this jig. It can be dangerous if you are not very careful using it. And sometimes I don’t use it the best way. You should watch this video about circular saw kick back: https://youtu.be/-VTwi9lI8N4
Advice: Making perfect miter joints is more difficult than it seems to be. This miter jig will be as good as your skills making it are. Theory is easy, but each mistake you make will be multiplied by 4. Making not perfect miter joints can be frustrating, but woodworking is just a hobby to me, so if this is your case just keep calm. It is up to you to decide if it is good enough to you. Sometimes it is better to accept what we can make than having an unfinished project. And if you are a professional…. well, you know mastery is a question of knowledge and lots of practise.
Gluing and clamping miter joints can be very difficult, too. I will use these Wolfcraft strap clamps. They are very useful, and sometimes easier to use than typical clamps. And we can use them to many other tasks, too. They are great to restrain big things inside the car trunk.
And why do I use two wooden bars to make the miter cuts?. We need both because sometimes we want to cut a moulding. Mouldings only have a flat surface to rest on the jig, so we need the possibility to cut from both sides of the jig.