Table Saw Miter Cutting Jig
When I was making my TV stand, I designed the doors with miter corners. To cut these corner I made a Miter cutting jig. This jig cut perfect miter corners and didn't take long to make.
I used a ¾” Baltic Birch piece of plywood (15-7/8” X 13-1/4”). ½” plywood could be used be I didn't’t have a piece the size I needed. It’s an unusual size because I didn't’t cut the piece I had on hand. I cut some cherry wood; I had on hand, and cut it to size to use as the miter sled. The miter guide bars came to ¾” wide X 5/16” deep X 19-3/8” long.
I read different articles about building one of these sleds, and some talking about aligning the plywood exactly at 90 degrees to the miter slots. I don’t see a need for this because even it you install the plywood at an angle it still wouldn't’t matter. The key to the jig's accuracy is installing the miter fences precisely at 90°.
First place one miter slide bar into each slot on your saw table. Align the ¾” or ½” plywood base on top of the guide, the longer edges should be perpendicular to the miter slots. With the plywood resting on the table saw surface, use a 5/32" drill bit to drill holes through the plywood and into the guides just far enough to mark their positions. Remove the plywood and guides. Drill completely through the guides and countersink the bottom of the guides so the head of the screw is below the surface of the wooden guide. I used #8 X 1-1/4” screws. I put two screws into each miter guide.
I screwed the miter bars in place then tested the fit on the table. The fit was a little tight so I adjusted one of the miter guides by moving one of the screws just slightly. The miter slides just need to slide smoothly but still fit tightly in the slots. One I was satisfied with the fit, I put the jig in place on the table saw. I proceeded to cut a slot halfway across the width of the plywood.
If you use a combination square to set this jig up, first make sure your combination square is accurate. To do this draw a line along one edge of the blade, flip the square over, and draw another line direct over the first line. If the two lines line up it is square, if not use something else. I started with my Starrett combination square. I'm a big fan of Starrett. Their stuff is expensive but the best quality.
Align the combination square with the cut in the wood and mark a 45 degree line. I used two pieces of a Kiln dried Douglas fir that I had on hand. Since I now have a jointer, I flattened all the sides so they would be square. Each piece was 1-3/8” X 1-3/8” X 12-1/4”. It just happened to come out square but there’s no reason it needs to be square.
I attached the right fence piece first. I drilled these pieces the same way I did the miter bar guides. I drilled completely through the wood until I hit the plywood. I removed the wooden fence and finished drilling through the plywood. I countersunk the bottom of the plywood and screwed the fence in place.
Once the right fence piece was in place, I ran the jig through the table saw so it cut the tip of the fence off at a 45 degree angle.
I then set my table saw miter guide at 45 degrees and cut the tip of the left fence piece at a 45 degree angle. I tried to use my combination square to mark the left side but it didn't’t seem accurate enough so I used my digital iGaging digital protractor. I highly recommend getting one of these. They aren't’t that expensive and I end up using it all the time.
This is the most important set because the jig must be set at 90 degrees. If the right fence piece wasn't’t set exactly at 45 degrees its OK but when both fences are in place, it must be at 90 degrees.
I lined the 45 degree cut of the left fence with the cut line in the plywood from the table saw blade. I screwed in one screw toward the front of the fence, so I could still pivot the back of the fence. After using the digital protractor to set the fence in place, I used some clamps to clamp the fence in place. Once secured, I turned the board over and screwed the fence in place.
I did a test cuts in 4 pieces of scrap wood and made a square. I was satisfied with the results. The last thing I did was to us double sided tape to attach 100-grit sandpaper to the fence faces.
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