Compound miter instructions for woodturners
This article describes how to make compound miters. You can make a single ring or a whole bowl. The advantage of compound mitering over normal segmenting is you can make an entire bowl from a board relatively quickly. This article assumes you can already build a flat segmented ring. If not a segmenting software program is highly recommended.
There are a few decisions to be made before you start. First you need to decide how many compound segments you want to use. Under normal circumstances that would be 8 or 12 but you can use more or less depending on your design. I most often try to stay with 12 segments if I can.
Next you need to decide the slope. This can be almost anything in decorative woodturnings. I measure slope from the horizontal. That would mean that the flat of your tabletop is 0 degrees and straight up would be 90 degrees. Anything in between would work for a bowl but when you get near 90 you would be a bit steep. If you went near 10 you would be very flat. So, Something around 30-45 would look more normal.
The last thing to think about is the bowl diameter. This depends on the width of the board you are using. As an example if you decided on a 40 degree slope a 4" wide board would make about a 7-7/8" diameter. 5" would be about 9-3/4 and 6" would be about 11-1/4". The segment length is the same as a basic flat ring.
The very best way to do your planning is to have a program like woodturner pro. This takes all the guess work away as you can see on your screen what your going to get. And the dimensions are all done. If you don't have the program there are other alternatives for getting the compound settings. This chart at better woodworking will work. Just pick your slope and the amount of sides and the chart will give you your settings.
The example I'm going to show here is a compound miter ring that I am currently building for a project that I am doing. Here the design calls for the blade to be tipped to 13.33 degrees and the sled set to 6.94. I actually don't use those exact numbers. For 13.33 I set the blade tilt 1/3 of the way between 13 and 14 degrees. For the 6.94 miter setting I used 7 degrees. 6.94 is only 6/100 shy of 7 which is near nothing. The picture below shows the first cut completed.
The next picture shows the board stood up and the segment length marked. Again the segment length is the same as a flat ring. If you don't know how to get this length you need a drawing program like woodturner pro or you need to draw the ring on a piece of paper and measure. Using Pi is an alternative but your ring will come out smaller being the ring is not round but segmented.
You'll notice above I extended the segment length line with a bevel. I did this so I can line up the tooth on the blade that matches this angle direction. Every other tooth on most blades are set in a different direction. I want to be sure to use a tooth aimed in this direction for every cut. The picture below shows this.The view is straight down.
The next picture below shows the board back in the sled ready for the second cut. Notice the board has been flipped. From here just continue to flip the board with each cut until you have enough segments.
Next we need to glue them together. The picture below shows the first 2 segments glued together. Notice there aren't any clamps. Clamps are never needed in gluing segments together. Put glue (titebond-2) on one face then rub the segments together until you feel resistance. At that point line them up and stop. Now put 2 small drops of CA (cyanoacrylate) glue on the inside of the segments. Immediately shoot the CA with accelerator. Push the segments together firmly for about 20 seconds. Now flip it over and do the same to the other side. The segments are now glued together well enough that you can set them aside to dry. The picture below shows the CA.
Now all thats left is gluing the balance of the segments together in 2 half circles. We use 2 halves so we can correct any error in the segments by sanding the half rings on a disc sander. The last picture below shows the 2 completed halves.
Thanks for taking the time to read my article. Bob