I want to make a doll house for my daughter.
I want to copy a "lighthouse" dollhouse I saw in a glass case.
It is half a decagon (5 sides) in shape. Open at the back for play. It is about 3 feet tall.
It is slightly smaller at the top (10" wide) then at the base (11" wide).
I am a junior woodworker. I have a table saw.
Questions:
1. How can I measure and layout a half decagon on plywood?
2. How can I determine what angle to cut the vertical sides so they are nice mitered corners?
3. As the sides rise from bottom to top they will have to be cut so that they somehow fold in towards the top since the top is smaller than the base. How can I determine that angle?
Best Answer
What you are looking to do is create a "compound miter" cut down the sides of each board. When someone mentions compound miters, they are typically trying to install crown moulding. The moulding sits at an angle between the wall and the ceiling and also meets itself at an angle on in corners. You want the same thing, but with vastly different angles.
If you search, you can find several "compound miter calculators" online, such as this one:
http://www.pdxtex.com/canoe/compound.htm
You need to put in two known angles, and it will tell you a miter and bevel to set the saw at to give the desired result.
The two angles you need is the angle the pieces will meet at, and the angle the pieces naturally sit. For moulding, the angle it sits against the wall is called the "spring angle", and is typically around 30-45 degrees.
Your pieces have a much shallower slope. They will rise 36" and have a run of 1" (or 1/2" depending on how I interpret your description, lets assume 1"). The page I linked to also has a handy slope calculator that tells us the pieces will set at 88.4 degrees.
Your pieces will meet at a 144 degree angle, but the calculator I found is nice enough to allow you to enter 10 sides and it figures that out for you. This comes from 360 degrees (circle) divided by 10 sides = 36 angles per side. The sides "meet" at the complementary angle which is 180 - 36 = 144.
So, taking all of that and hitting calculate, we see that you need to set your blade at a 17.99 degree angle, and set a jig to "miter" the board at a 0.52 degrees. Of course on the jig it's going to be easier to just measure the 1" difference from top to bottom than to measure half of a degree.