This is a repost of a response to an old thread on how to put together a multi sided frame. I took some time answering, but realized it would soon disappear. so here is my response, along with a pdf of the calculations and other hints for making these complex frames or even solid tops. Enjoy.
My best, most accurate solution has been to use the Rockler table saw sled, picture below. It has a swing arm with extremely precise markings for the angle of the fence. It's all in the setup. I set it up so Zero is perfectly 90 to the full kerf blade, and that the blade is perfectly parallel to the miter slots. On this once you set the fence 90 to the blade, you then move the indicator so it is on the zero line. After that, you can cut any angle you wish, and it's markings are sufficiently far apart so you can do half and even a quarter of a degree cuts with astonishing accuracy.
If you are going for ridiculous accuracy, you can clamp the workpiece to the fence because it can slip slightly. Add a strip of self adhesive sandpaper to the front of the swinging fence. Use a stop block to get all pieces to the same length.
At the bottom is a pdf of the Rockler file on calculating to determine length of each piece to get a particular diameter. I would precut to a little over the desired lengthy, then cut one end to half the angle required, then place the stop block in position and then cut the other end. Thank Rockler for the pdf by buying stuff from them. I don't get a toaster from them, but they are the only woodworking store withing driving range, so I have a lot of their stuff.
Here is a picture of the Freud Industrial Glue Line blade. It is a rip blade but does an equally great job on end grain. It also has an ample amount of carbide, so it can be resharpened many times. It also has every fourth carbide cut flat so it is excellent for 1/8th spline cutting.
I tried for some time to get perfect miter cuts, but found the thin kerf blades would deflect slightly so the angled faces didn't quite meet. I also suggest using a full kerf Glue Line blade for ultra smooth gluing surfaces. Put one coat of glue on the ends, let it dry, then do the finished glue up. This will improve the joint strength. Use the dries clear glue for this application.
Hope this is helpful. By the way, Rockler makes a great, thick draftsman's triangle, clear plastic with a 90 and 45 angle that are right on. I use it all the time. Really handy.
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