September 04, 2013

Circular saw miter cut jig

Circular saw miter cut jig, rummageinthegarage
Joining together two pieces of wood at a 45º angle or miter cut doesn´t seem to be a very difficult task. 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.


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 centimeters 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 it is better to to use a planer to make sure all the boards are the same dimensions.

I can´t afford a planer so I made a homemade planer with my electric hand jointer.

Faber Castell green square, rummageinthegarage
Miter cut jig, rummageinthegarageNext we need to make the most perfect miter cuts we can. We can use a miter saw that we must perfectly adjust 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 it we need to make a homemade 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.

Frame with 45 degrees joints, rummageinthegarage
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.

Advice: Making perfect miter joints is more difficult than it seems to be. This 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.


Video with subtitles in English:

Wolfcraft strap, rummageinthegarage
Gluing and clamping miter joints can be very difficult, too. I will use these Wolfcraft straps. They are very useful, 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.